U.S. patent application number 13/180604 was filed with the patent office on 2012-10-04 for optical element producing a modulated region of decreased light intensity and optically enhanced photovoltaic cell including the same.
This patent application is currently assigned to E.I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to REBEKAH ANN DERRYBERRY, ROGER HARQUAIL FRENCH, MARK E. LEWITTES, RONALD JACK RIEGERT, JOSE MANUEL RODRIGUEZ-PARADA.
Application Number | 20120248559 13/180604 |
Document ID | / |
Family ID | 45816619 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120248559 |
Kind Code |
A1 |
DERRYBERRY; REBEKAH ANN ; et
al. |
October 4, 2012 |
OPTICAL ELEMENT PRODUCING A MODULATED REGION OF DECREASED LIGHT
INTENSITY AND OPTICALLY ENHANCED PHOTOVOLTAIC CELL INCLUDING THE
SAME
Abstract
An optical element has a plano-plano body formed of a first
material having a greater refraction index n.sub.1 and a second
material having a lesser refraction index n.sub.2. Both indices are
greater than one. The absolute value of the index contrast,
log.sub.10(n.sub.1/n.sub.2), is in the range from about 0.001 to
about 0.17, preferably from about 0.01 to about 0.05. The materials
have an induced absorbance rate .DELTA.Abs/Dose less than or equal
to about 0.4, preferably less than or equal to about 0.2. The
materials are arranged such that an interface with at least one
cusp is defined therebetween. The cusp has an apex pointed toward
the material having the greater index of refraction. The cusp is
operative to produce a region of decreased light intensity on one
surface of the optical element in response to light incident on the
other surface of the optical element.
Inventors: |
DERRYBERRY; REBEKAH ANN;
(WILMINGTON, DE) ; FRENCH; ROGER HARQUAIL;
(CLEVELAND HEIGHTS, OH) ; LEWITTES; MARK E.;
(WILMINGTON, DE) ; RIEGERT; RONALD JACK; (NEWARK,
DE) ; RODRIGUEZ-PARADA; JOSE MANUEL; (HOCKESSIN,
DE) |
Assignee: |
E.I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
45816619 |
Appl. No.: |
13/180604 |
Filed: |
July 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61363758 |
Jul 13, 2010 |
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61363764 |
Jul 13, 2010 |
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61363769 |
Jul 13, 2010 |
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61363773 |
Jul 13, 2010 |
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61363778 |
Jul 13, 2010 |
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61363784 |
Jul 13, 2010 |
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Current U.S.
Class: |
257/432 ;
257/E31.127; 359/619 |
Current CPC
Class: |
Y02E 10/52 20130101;
G02B 3/0056 20130101; H01L 31/0543 20141201; G02B 3/0043
20130101 |
Class at
Publication: |
257/432 ;
359/619; 257/E31.127 |
International
Class: |
H01L 31/0232 20060101
H01L031/0232; G02B 27/12 20060101 G02B027/12 |
Claims
1. As an article of manufacture, an optical element comprising: a
body having a first portion and a second portion, the first portion
being formed from a first material having an index of refraction
n.sub.1, the second portion being formed from a second material
having an index of refraction of refraction n.sub.2, one index of
refraction being greater than the other index of refraction, with
both indices of refraction being greater than the index of
refraction of air, each portion of the body having a substantially
planar exterior surface formed thereon, each surface defining one
of a pair of opposed major surfaces of the optical element, the
first and second portions being arranged such that an interface
with at least one cusp is defined within the optical element
between the first and second materials, the cusp having an apex
pointed toward the material having the greater index of refraction,
the cusp being operative to produce a region of modulated light on
one surface of the optical element in response to light incident on
the other surface of the optical element.
2. The optical element of claim 1 wherein the first and second
materials have an index contrast "c" defined by the relationship:
c=log.sub.10 n.sub.R, where n.sub.R=(n.sub.1/n.sub.2), wherein the
absolute value of c lies within the range from about 0.001 to about
0.17, such that 0.001<|c|<0.17.
3. The optical element of claim 2 wherein the absolute value of "c"
lies within the range from about 0.01 to about 0.05, such that
0.01<|c|<0.05.
4. The optical element of claim 1 wherein the materials have an
induced absorbance rate .DELTA.Abs/Dose less than or equal to about
0.4.
5. The optical element of claim 4 wherein the materials have an
induced absorbance rate .DELTA.Abs/Dose less than or equal to about
0.2.
6. As an article of manufacture, an optical element comprising: a
body having a first portion and a second portion, the first portion
being formed from a first material having an index of refraction
n.sub.1, the second portion being formed from a second material
having an index of refraction of refraction n.sub.2, one index of
refraction being greater than the other index of refraction, with
both indices of refraction being greater than the index of
refraction of air, each portion of the body having a substantially
planar exterior surface formed thereon, each surface defining one
of a pair of opposed major surfaces of the optical element, the
first and second portions being arranged such that an interface
with at least one cusp is defined within the optical element
between the first and second materials, the cusp having an apex
pointed toward the material having the greater index of refraction,
the cusp being operative to produce a region of modulated light on
the surface of the optical element having the greater index of
refraction in response to light incident on the surface of the
optical element having the lesser index of refraction.
7. The optical element of claim 6 wherein the first and second
materials have an index contrast "c" defined by the relationship:
c=log.sub.10 n.sub.R, where n.sub.R=(n.sub.1/n.sub.2), wherein the
absolute value of c lies within the range from about 0.001 to about
0.17, such that 0.001<|c|<0.17.
8. The optical element of claim 7 wherein the absolute value of "c"
lies within the range from about 0.01 to about 0.05, such that
0.01<|c|<0.05.
9. The optical element of claim 6 wherein the materials have an
induced absorbance rate .DELTA.Abs/Dose less than or equal to about
0.4.
10. The optical element of claim 9 wherein the materials have an
induced absorbance rate .DELTA.Abs/Dose less than or equal to about
0.2.
11. As an article of manufacture, an optical element comprising: a
body having a first portion and a second portion, the first portion
being formed from a first material having an index of refraction
n.sub.1, the second portion being formed from a second material
having an index of refraction of refraction n.sub.2, one index of
refraction being greater than the other index of refraction, with
both indices of refraction being greater than the index of
refraction of air, each portion of the body having a substantially
planar exterior surface formed thereon, each surface defining one
of a pair of opposed major surfaces of the optical element, the
first and second portions being arranged such that an interface
with at least one cusp is defined within the optical element
between the first and second materials, the cusp having an apex
pointed toward the material having the greater index of refraction,
the cusp being operative to produce a region of modulated light on
the surface of the optical element having the lesser index of
refraction in response to light incident on the surface of the
optical element having the greater index of refraction.
12. The optical element of claim 11 wherein the first and second
materials is have an index contrast "c" defined by the
relationship: c=log.sub.10 n.sub.R, where
n.sub.R=(n.sub.1/n.sub.2), wherein the absolute value of c lies
within the range from about 0.001 to about 0.17, such that
0.001<|c|<0.17.
13. The optical element of claim 12 wherein the absolute value of
"c" lies within the range from about 0.01 to about 0.05, such that
0.01<|c|<0.05.
14. The optical element of claim 13 wherein the materials have an
induced absorbance rate .DELTA.Abs/Dose less than or equal to about
0.4.
15. The optical element of claim 14 wherein the materials have an
induced absorbance rate .DELTA.Abs/Dose less than or equal to about
0.2.
16. An enhanced photovoltaic cell comprising: a photovoltaic cell
having at least one semiconductor junction operative to produce
electrical energy in response to incident radiation, the
photovoltaic cell having at least one obstruction to incident light
on a planar surface thereof; and a plano-plano optical element one
surface of which is mounted to the surface of the photovoltaic cell
in a light transmission path between a source of light and the
surface of the photovoltaic cell having the obstruction thereon,
the plano-plano optical element itself comprising: a body having a
first portion and a second portion, the first portion being formed
from a first material having an index of refraction n.sub.1, the
second portion being formed from a second material having an index
of refraction of refraction n.sub.2, one index of refraction being
greater than the other index of refraction, with both indices of
refraction being greater than the index of refraction of air, each
portion of the body having a substantially planar exterior surface
formed thereon, each surface defining one of a pair of opposed
major surfaces of the optical element, the first and second
portions being arranged such that an interface with at least one
cusp is defined within the optical element between the first and
second materials, the cusp having an apex pointed toward the
material having the greater index of refraction, the cusp being
operative to redirect and to produce a region of modulated light
exiting one surface of the optical element in response to light
incident on the other surface of the optical element, the region of
modulated light being aligned with the obstruction on the
photovoltaic cell while the redirected light is incident upon
another region of the surface of the photovoltaic cell.
17. The enhanced photovoltaic cell of claim 16 wherein the first
and second materials of the optical element have an index contrast
"c" defined by the relationship: c=log.sub.10 n.sub.R, where
n.sub.R=(n.sub.1/n.sub.2), wherein the absolute value of "c" lies
within the range from about 0.001 to about 0.17, such that
0.001<|c|<0.17.
18. The enhanced photovoltaic cell of claim 17 wherein the absolute
value of "c" lies within the range from about 0.01 to about 0.05,
such that 0.01<|c|<0.05.
19. The enhanced photovoltaic cell of claim 16 wherein the
materials of the optical element have an induced absorbance rate
.DELTA.Abs/Dose less than or equal to about 0.4.
20. The enhanced photovoltaic cell of claim 16 wherein the
materials have an induced absorbance rate .DELTA.Abs/Dose less than
or equal to about 0.2.
21. The enhanced photovoltaic cell of claim 16 further comprising a
heat sink connected to the photovoltaic cell.
22. The enhanced photovoltaic cell of claim 21 further comprising a
submount disposed between the heat sink and the photovoltaic cell.
Description
CLAIM OF PRIORITY
[0001] This application claims priority from each of the following
United States Provisional Applications, each of which is hereby
incorporated by reference:
[0002] (1) Optical Element Producing A Modulated Region of
Decreased Light Intensity, Application Ser. No. 61/363,758, filed
13 Jul. 2010 (CL-4997);
[0003] (2) Optical Element Producing A Modulated Region of
Increased Light Intensity, Application Ser. No. 61/363,764, filed
13 Jul. 2010 (CL-5148);
[0004] (3) Optically Enhanced Photovoltaic Cell Including An
Optical Element Producing A Modulated Region of Decreased Light
Intensity, Application Ser. No. 61/363,769, filed 13 Jul. 2010
(CL-5149);
[0005] (4) A Display Device Including An Optical Element Producing
A Modulated Region of Increased Light Intensity, Application Ser.
No. 61/363,773, filed 13 Jul. 2010 (CL-5150);
[0006] (5) An LED Lighting Device Including An Optical Element
Producing A Modulated Region of Increased Light Intensity,
Application Ser. No. 61/363,778, filed 13 Jul. 2010 (CL-5158);
and
[0007] (6) Photovoltaic Apparatus Including An Optical Element
Producing A Modulated Region of Light Intensity, Application Ser.
No. 61/363,784, filed 13 Jul. 2010 (CL-5159).
CROSS-REFERENCE TO RELATED APPLICATIONS
[0008] Subject matter disclosed herein is disclosed in the
following copending applications, all filed contemporaneously
herewith and all assigned to the assignee of the present
invention:
[0009] Optical Element Having Internal Inclusions Configured For
Maximum Conversion Efficiency, application Ser. No. ______, filed
Jul. 13, 2011 (CL-5294, a cognate of CL-5294 and CL-5444);
[0010] Photovoltaic Assemblies Incorporating An Optical Element
Having Internal Inclusions Configured For Maximum Conversion
Efficiency, application Ser. No. ______, filed Jul. 13, 2011
(CI-5443, a cognate of CL-5443 and CL-5445);
[0011] Optical Element Producing A Modulated Region of Increased
Light Intensity and Optically Enhanced Photovoltaic Cell and LED
Lighting Device Including The Same, application Ser. No. ______,
filed Jul. 13, 2011 (CL-5148, a cognate of CL-5148, CL-5150 and
CL-5158); and
[0012] Photovoltaic Apparatus Including An Optical Element
Producing A Modulated Region of Light Intensity, application Ser.
No. ______, filed Jul. 13, 2011 (CL-5159).
BACKGROUND OF THE INVENTION
[0013] In the area of photovoltaics, the active photovoltaic ("PV")
cell in many cases has metallic conductor lines on the front,
sun-facing, surface of the cell. These conductor lines are
essential to the electrical circuit of which the PV cell is an
element. However, at the same time, these front side metallic
conductor lines cause a portion of the incident solar radiation to
be blocked from entering the active semiconductor absorber
materials in the cell, and therefore do not contribute to the
photovoltaic current produced by the cell.
[0014] These optical losses in photovoltaic conversion due to the
presence of front side conductor lines are found in many different
types of photovoltaics, from PV modules designed for use at 1
kW/m.sup.2 irradiance (where 1 kW/m.sup.2 is approximately the
irradiance of the sun at the surface of the earth) to concentrating
photovoltaic ("CPV") modules in which the solar radiation is
concentrated to 5, 50, or even greater than 500 times the
irradiance of the sun and focused on higher efficiency PV
cells.
[0015] In an effort to overcome the loss of electrical power from
the PV module due to obscuration of the front side of the PV cell
by the front side conductors some PV cells dispose all the cell
conductor lines away from the front side of the PV cell. These
approaches are typically referred to as "back side contacting PV
cells", and require extensive redesign of the PV cell with
increased complexity and cost.
[0016] In others areas, such as in LCD display devices and LED
lighting devices, there is a need to decrease the spatial
modulation of light to provide more uniform illumination from the
devices.
[0017] Accordingly, in view of the foregoing it is believed to be
advantageous to provide an article in the form of an optical
element which could be used in conjunction with a photovoltaic, LCD
and/or LED device and which serves to harvest substantially all of
the radiation incident on the article and which is also able to
redirect that incident light toward or away from certain regions of
interest on the device.
[0018] Such an article, when used in conjunction with a
photovoltaic cell, could redirect the light away from the front
side conductor lines and towards the active semiconductor materials
of the PV cell, so that this light will contribute to the
electrical output of a PV cell, module and system.
[0019] When used in conjunction with an LCD display and/or LED
lighting device, such an article could be used to provide more
uniform illumination in otherwise dark regions of the LCD display
device. In the LED lighting case the optical element may be used to
make the point source-like-nature of the LED more homogeneous and
uniform. [0020] -o-0-o-
[0021] Considering again the area of photovoltaics, in addition to
the matter of light collection efficiency discussed above, another
critical consideration is radiation durability.
[0022] Radiation durability refers to the ability of a material
from which an article is made, to withstand a predetermined level
of irradiance for the desired lifetime of the article. Thus, a flat
plate module (i.e., a module designed for use at 1 kW/m.sup.2
irradiance) must be able to withstand an irradiance of 1 KW/m.sup.2
of solar radiation for the desired lifetime (typically twenty-five
years) of the PV module and system.
[0023] In the case of CPV modules the radiation durability
requirements are more stringent since for an identical lifetime,
the irradiance of light is much higher, and the total dose of solar
radiation into the materials on the front side of the PV cell in
concomitantly larger, by the concentration factor.
[0024] Accordingly, is it believed to be of further advantage that
an optical element that redirects light to enhance light collection
efficiency is, at the same time, also radiation durable for the
application and lifetime for which it is used.
SUMMARY OF THE INVENTION
[0025] An optical element article in accordance with the present
invention, when utilized in PV and many other applications,
satisfies the need to spatially modulate the intensity of light
while exhibiting the requisite radiation durability for the
application. The optical element has a plano-plano structure, i.e.,
it has two flat exterior surfaces. Owing to the configuration of
the internal interface between the two materials forming the
optical element, light incident on one side of the optical element
is spatially modulated as a result of traveling through the
plano-plano optical element.
[0026] The plano-plano nature of the optical element enables it to
be incorporated on to a diverse number of different PV cells, and
then to be integrated into the rest of the PV module, without
requiring redesign of the module. In addition, the plano-plano
nature of the optical element article means that it can be easily
incorporated with other optical elements, such as secondary optics
of the homogenizer or concentrator types used in CPV applications.
These can also be easily incorporated into other optical systems
with minimal configuration changes to the system.
[0027] The optical element is made from two materials, each with a
respective index of refraction. One index of refraction is greater
than the other index of refraction, with both indices of refraction
being greater than the index of refraction of air. The internal
interface between the first and second materials is arranged such
that an interface with at least one, but more preferably a
plurality, of cusp(s) is defined therebetween. Based upon the
direction in which the apex of the cusp(s) are oriented, each cusp
produces a region of modulated light, with the desired width and
periodicity of the modulated regions, on the side of the optical
element opposite to the incident light side.
[0028] Due to the difference in indices of refraction, an index
contrast parameter "c" is defined between the two materials, where
c defined by the relationship
c=log.sub.10 n.sub.R, where n.sub.R=(n.sub.1/n.sub.2).
In accordance with the present invention materials forming the
optical element are selected such that the absolute value of index
contrast "c" lies within the range from about 0.001 to about 0.17,
and more preferably, in the range from about 0.01 to about
0.05.
[0029] Materials forming the optical element are also selected to
provide sufficient radiation durability, that is, lifetime at the
irradiance of the application (from 1 KW/m.sup.2 to >500
KW/m.sup.2 concentration). These material selections are made based
on the induced absorbance rate (.DELTA.Abs/Dose) of the different
materials at the required irradiance level of the application. In
accordance with the invention the materials have an induced
absorbance rate (.DELTA.Abs/Dose) less than or equal to about 0.4,
and more preferably, less than or equal to about 0.2.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The invention may be more fully understood from the
following detailed description, taken in connection with the
accompanying drawings, which form part of this application and in
which:
[0031] FIGS. 1A and 1B are, respectively, a stylized pictorial
front section view and a side elevation view of an optical element
article in accordance with one embodiment of the present
invention,
[0032] FIGS. 1C and 1D are diagrammatic plan and section views
showing an alternative arrangement of the optical element wherein
the cusps are formed as closed features within the body of the
element;
[0033] FIGS. 2A and 2B are stylized pictorial front section views
showing the patterns of modulated regions of light produced by an
optical element having an interface oriented as in FIG. 1A when the
apices of the cusps of the interface therein are directed toward
the material having the greater index of refraction and the
material having the lesser index of refraction, respectively;
[0034] FIGS. 3A and 3B are, respectively, a stylized pictorial
front section view and a side elevation view (similar to FIGS. 1A,
1B) of an optical element article in accordance with a second
embodiment of the present invention;
[0035] FIGS. 4A and 4B are stylized pictorial front section views
similar to FIGS. 2A, 2b showing the patterns of modulated regions
of light produced by an optical element having an interface
oriented as in Figure sA when the apices of the cusps of the
interface therein are directed toward the material having the
greater index of refraction and the material having the lesser
index of refraction, respectively;
[0036] FIG. 5A is stylized pictorial representation viewed in a
vertical plane illustrating one example of an arbitrary
configuration of a cusp, while FIG. 5B is an enlarged view of the
circled portion at the apex of the cusp in FIG. 5A;
[0037] FIG. 6 is stylized pictorial representation viewed in a
vertical plane illustrating another example of an arbitrary
configuration of a cusp;
[0038] FIG. 7A is stylized pictorial representation viewed in a
vertical plane illustrating yet another example of an arbitrary
configuration of a cusp, while FIG. 7B is an enlarged view of the
circled portion at the apex of the cusp in FIG. 7A;
[0039] FIGS. 8A through 8C illustrate stylized pictorial
representations of alternative arrangements of materials M.sub.1,
and M.sub.2 of the optical elements, in which more than one region
of a given material may be disposed within the body of the
element;
[0040] FIGS. 9A through 9C illustrate stylized schematic
representations of low, medium and high concentration CPV modules,
respectively, that include an optical element in accordance with
the present invention;
[0041] FIG. 10 is a stylized schematic representation of an
integrated photovoltaic cell assembly that includes an CPV cell
with secondary optics, a heat sink, and an optical element in
accordance with the present invention;
[0042] FIG. 11 is a stylized schematic representation of a flat
plate PV apparatus that includes a photovoltaic cell with a front
side metallization, and optical element in accordance with the
present invention;
[0043] FIG. 12A is a definitional drawing illustrating the
geometrical parameters for a dark line optical element in
accordance with the present invention in which material 1 has the
lower index of the pair of materials (n.sub.1/n.sub.2)<1;
[0044] FIG. 12B is a definitional drawing similar to FIG. 12A
illustrating the geometrical parameters for a dark line optical
element in accordance with the present invention in which material
1 has the higher index of the pair of materials
(n.sub.1/n.sub.2)>1;
[0045] FIGS. 13A through 13C are design maps used for constructing
a minimal interface for an optical element in accordance with the
present invention;
[0046] FIG. 14A is a three-dimensional rendering of the structure
of the optical element of Example 12, while FIG. 14B is a portion
of the cross section of this structure and the intensity
profile;
[0047] FIG. 15A is a three-dimensional rendering of the structure
of the optical element of Example 13, while FIG. 15B is a portion
of the cross section of this structure and the intensity
profile;
[0048] FIG. 16A is a three-dimensional rendering of the structure
of the optical element of Example 14, while FIG. 16B is a portion
of the cross section of this structure and the intensity
profile;
[0049] FIG. 17A is a three-dimensional rendering of the a portion
of a Reflexite.RTM. film used in Example 15, while FIG. 17B is a
three-dimensional rendering of the a portion of a Reflexite.RTM.
film covered with a silicone polymer layer, and FIG. 17C is a
portion of the cross section of this structure and the intensity
profile; and
[0050] FIG. 18 is a portion of the cross section of the structure
of Example 16 and the resulting intensity profile.
DETAILED DESCRIPTION OF THE INVENTION
[0051] Throughout the following detailed description similar
reference numerals refer to similar elements in all figures of the
drawings.
[0052] With reference to FIGS. 1A, 1B and FIGS. 3A, 3B shown are
stylized pictorial representations of two optical element articles,
generally indicated by the reference characters 10 and 10',
respectively, each in accordance with the present invention. The
optical element 10, 10' may also be referred to herein as "CLOE".
FIGS. 1A and 3A are front elevation views of the articles 10, 10'
while FIGS. 1B and 3B are corresponding side elevation views
thereof. Although FIGS. 1A and 3A are intended as front section
views, the section lines have been omitted for clarity of
illustration.
[0053] Each optical element article 10, 10' comprises a body 12
having a first portion 14A formed of a first material M.sub.1 and a
second portion 14B formed of a second material M.sub.2. Each
material has a respective index of refraction n.sub.1 and n.sub.2.
One index of refraction is greater than the other index of
refraction, with both indices of refraction being greater than the
index of refraction of air.
[0054] A useful parameter for later discussion is the index
contrast parameter "c" defined between the two materials, where c
given by the relationship:
c=log.sub.10 n.sub.R, where n.sub.R=(n.sub.1/n.sub.2).
[0055] The body 12 may assume any generalized three-dimensional
shape so long as it includes first and second substantially planar,
opposed major surfaces 16A, 16B, thereby defining a plano-plano
optical element. In the preferred instances the major surfaces 16A,
16B are substantially parallel to each other, but this orientation
is not required. That is to say, the surfaces 16A, 16B may be
inclined with respect to each other.
[0056] The first material and the second material are arranged
within each optical element 10, 10' such that an interface 20 is
defined through the optical element between the first and second
materials M.sub.1 and M.sub.2. In the arrangements illustrated in
FIGS. 1 and 3, the interface 20 extends throughout the entire
length and breadth of the body of the optical element.
[0057] The interface 20 is configured to exhibit one or more
cusp(s) generally indicated by the reference character 22. In FIGS.
1A and 3A three such cusps 22-1, 22-1, 22-3 are shown. Any
convenient number of cusps may be formed along the interface, as
will be developed.
[0058] The cusps 22 may take any convenient form. In the
arrangements illustrated in FIGS. 1A, 3A the cusps define linear
features that extend axially through the entire body of the optical
element (i.e., into the plane of FIGS. 1A, 3A). Alternatively,
however, the cusps may extend sinuously along the axial direction
of the entire body.
[0059] As a further alternative, as diagrammatically illustrated in
FIGS. 10 and 1D, the cusps may be formed as closed features within
the body, for example, appearing as rectangles, or squares, circles
or ovals when the optical element 10, 10' is viewed in plan.
[0060] As a yet further alternative cusps may also be formed with
finite lengths within the body.
[0061] Although a somewhat more formal definition is provided
herein, in general, a cusp 22 includes a region having a contour
22R with refractive power that terminates in a generally pointed
apex 22A. In accordance with the invention the apex 22A is oriented
toward the portion of the body having either the first material or
the second material. The direction in which the apex points is
taken as the direction of the cusp. In the case illustrated in FIG.
1A each apex 22 of each cusp 22 is directed toward the portion of
the body formed of the second material M.sub.2. Alternatively, in
the instance illustrated in FIG. 3A the apex of each cusp defined
along the interface 20 therein is directed toward the portion of
the body formed of the first material M.sub.1.
[0062] Depending upon the relative magnitudes of the indices of
refraction n.sub.2 and n.sub.1, the direction of the apex
determines whether a modulated region of relatively higher or
relatively lower light intensity is produced on one surface of
material when the opposite surface of the optical element is
exposed to incident radiation.
[0063] For example, FIG. 2A illustrates the regions of modulated
light produced when an optical element whose interface is arranged
in the manner shown in FIG. 1A, (i.e., with the apices of the
interface directed toward the second material M.sub.2). (It should
be appreciated that in FIGS. 2A, 2B, 4A, 4B several representative
ray paths are illustrated in the drawings, from which the action of
each optical element 10, 10', as the case may be, to redirect light
incident thereon may be clearly understood.) When the index of
refraction n.sub.2 is greater than the index n.sub.1 of the first
material M.sub.1 the cusps 22 operate to direct light incident on
the first surface 16A away from certain portions of the second
surface 16B, thereby producing modulated regions 24D of relatively
lesser light intensity on the second surface 16B. The modulated
regions 24D of relatively lesser intensity may be referred to as
"dark lines". The dark lines 24D so produced extend along the
second surface of the optical element in a pattern that tracks the
configuration of the cusp.
[0064] Conversely, as shown in FIG. 2B, when the index of
refraction n.sub.2 of the second material M.sub.2 is less than the
index n.sub.1 of the first material M.sub.1 modulated regions 24B
of relatively greater intensity are produced on the second surface
16B of the element 10 when the first surface 16A thereof is exposed
to incident light. The modulated regions of relatively lesser
intensity may be referred to as "bright lines". The bright lines
also extend along the second surface of the optical element in a
pattern that tracks the configuration of the cusp.
[0065] As illustrated in FIGS. 4A and 4B similar situations obtain
when one surface of an optical element having the interface
arranged as in FIG. 3A (apices of the interface directed toward the
first material M.sub.1) is exposed to incident radiation. FIG. 4A
illustrates that when the index of refraction n.sub.1 is greater
than the index n.sub.2 modulated "dark line" regions 24D
(relatively lesser intensity) are produced on the second surface
16B of the element 10' when the first surface 16A thereof is
exposed to incident light. When the index of refraction n.sub.1 is
less than the index n.sub.2 modulated "bright lines" regions 24B
(relatively greater light intensity) are produced on the second
surface 16B of the element 10 when the first surface 16A thereof is
exposed to incident light.
[0066] With reference to FIGS. 5A, 5B, 6, 7A and 7B shown are
stylized cross section representations (taken along a vertical
plane through the element 10, 10') of three examples of arbitrary
configurations of cusps that may be formed along the interface
between the first and second materials. In these Figures one
surface (e.g., the first surface 16A) is substantially horizontal
as viewed in the Figures, and that a reference axis R extends
substantially perpendicularly to that surface.
[0067] As used in this application a cusp 22 is a portion of the
interface having a refractive contour 22R that terminates in a
generally pointed apex 22A. A cusp extends along the interface 20
between a first transition point and the next-adjacent transition
point. A transition point may be identified as a particular point
along the interface where a line perpendicular to a tangent to the
interface is parallel to a reference axis R, while the
perpendicular to the tangent of a point on either side of the
particular point is inclined with respect to the reference axis R.
The reference axis R is preferably chosen to be substantially
parallel to the predominant direction of light propagation in the
body. One transition point defines the onset of the cusp while the
next-adjacent transition point defines the apex of the cusp.
[0068] The definition becomes clearer when the stylized
representations of the various cusps shown in FIGS. 5A, 5B, FIG. 6
and FIGS. 7A, 7B are considered.
[0069] In FIGS. 5A and 5B points A, B, C, D and E are identified
along the interface defined within the element. Perpendicular lines
L.sub.A, L.sub.B, L.sub.C, L.sub.D, and L.sub.E are erected to
tangents T.sub.A, T.sub.B, T.sub.C, T.sub.D, and T.sub.E at each
respective point A, B, C, D and E. It should be noted that in an
actual implementation of the optical element, due to physical
limitations of optical tooling and fabrication methods, the point E
is not a unitary point, but is, in fact (as shown in FIG. 5B), a
pair of points E, E' separated by a small interface region U. The
region U could be planar, curved or arbitrarily rough.
[0070] At points A, C and D the lines L.sub.A, L.sub.C and L.sub.D
are inclined with respect to reference parallel lines R.sub.A,
R.sub.C and R.sub.D (each parallel to the reference axis R). This
indicates that the contour at these points have refractive
power.
[0071] However, at points B and E, the lines L.sub.B and L.sub.E
align with respect to reference parallel lines R.sub.B and R.sub.E.
The point B thus defines a transition point because the
perpendicular to the tangent at points A and C on both sides of
point B are inclined with respect to the reference axis R. The
point E is a transition point because at some point X in the region
U the perpendicular to the tangent at point X is parallel to the
reference axis.
[0072] Once adjacent transition points (e.g., points B, E) are
located along the interface, each point is tested to determine
whether it is to be treated an onset point of the cusp or the apex
of the cusp. Two test points lying between the identified
transition points are selected, one test point lying close to one
transition point (e.g., point C) and the other test point lying
close to the other transition point (e.g., point D). The magnitude
of the angle of inclination of the perpendicular with respect to
the reference axis R at each test point is compared. The adjacent
test point having the greater angle of inclination (and, thus, the
greater refractive power) indicates that the adjacent transition
point is the apex of the cusp. The lesser angle of inclination
(indicating relatively lesser refractive power) identifies that the
adjacent transition point (point B) is an onset point. However, it
should be noted that the point B could also be considered as an
apex because the inclination angles of points near to point B do
exhibit some refractive power.
[0073] In FIG. 6 points G and J are again identified as transition
points. Point G is a transition point because the perpendicular to
the tangent at point H on the right side of point G is inclined
with respect to the reference axis R. The point J is a transition
point because the perpendicular to the tangent at point I on the
left side of point J is inclined with respect to the reference axis
R.
[0074] However, in this instance both points G and J constitute
apex points because the magnitude of the angle of inclination at
the test points H and I are equal.
[0075] With respect to the rising ramp at the right side of the
FIG. 6, similar reasoning shows that on the cusp having points K
through O, both points K and N are transition points, and both are
apex points.
[0076] The linear region V between points J and K defines a
non-refractive contour, and hence is not part of either cusp.
[0077] FIG. 7A, 7B thus presents a situation similar to that of
FIG. 6, differing only in the length of the non-refractive contour.
Owing to the limitations in tooling discussed above, point T is
really a pair of point T, T' separated by another small interfacial
region W.
[0078] As is illustrated in FIG. 5B, once a transition point is
identified as an apex, the direction of the apex is determined by
examination of the smaller included angle .theta. (i.e., the angle
less than 180.degree.) extant between tangents T.sub.E, and
T.sub.E' to the contour at points E, E' each side of the apex. The
bisecting line Z of that smaller included angle .theta., directed
toward the apex point, defines the direction of the cusp.
[0079] FIGS. 8A through 8C illustrate stylized pictorial
representations of alternative arrangements of materials M.sub.1,
and M.sub.2 of the optical elements. In these Figures more than one
region of a given material (e.g., the material M.sub.2) may be
disposed within the body 12 of the element 10/10'. [0080]
-o-0-o-
[0081] When light is incident on one side of the plano-plano
optical element, the light that exits the optical element on the
other side will be modulated. There are four versions of this
optical element, two which produces dark lines (FIGS. 2A, 4A),
where the modulation leads to a region of reduced intensity on the
exit side of the article, and others (FIGS. 2B, 4B), where the
light exiting the optical element has a region of increased
intensity. The application of this article can be to produce one
modulated region in the light on the exit side, or the internal
interface can be designed such that there is a periodic or
aperiodic array of modulated regions of light on the exit side of
the optical element.
[0082] For the photovoltaic ("PV') applications the typical
modulated width and periodicities that are characteristic of
concentrated photovoltaic ("CPV') applications and Flat Plate PV
applications are used. For typical semiconductor cells used in
high-concentrated photovoltaic ("H--CPV"), the front side conductor
lines are 10 microns in width, and they are spaced on the PV cell
with a periodic spacing of 100 microns. For typical crystalline
silicon flat plate PV cells the front side conductor lines are
typically 100 microns wide and their periodic spacing is typically
2000 microns.
[0083] The applications of this optical element are in the areas of
photovoltaics, with additional applications in displays, lighting
and other areas where spatial modulation of light is desirable. In
the area of photovoltaics, many types of PV are used where the
incident light irradiance can be 1 kW/m.sup.2 typically found in
flat plate PV modules of crystalline silicon, or thin film modules
of silicon, CdTe, CIGS or other semiconductors. In flat plate PV
modules the PV cell is typically encapsulated, such that the PV
cell and the materials in contact with it, are kept in an
environment with very low levels of oxygen or moisture, and this
fact is important in the radiation durability of the materials used
on the front side (the solar irradiated side) of the PV Cell.
[0084] In addition the area of concentrating photovoltaics (CPV) is
characterized by using optical systems to concentrate solar
radiation down onto small semiconductor PV cells, in which the
irradiance can vary from 1 kW/m.sup.2 to 10 kW/m.sup.2 for low
concentration, or 10 to 200 kW/m.sup.2 concentrations for medium
concentration PV, or 200 kW/m.sup.2 to 500 kW/m.sup.2 and even up
to >2000 kW/m.sup.2 concentrations for high concentration PV.
These CPV classifications are also characterized by the need for
the CPV module to mechanically track the sun during the day, so as
to continue collecting light, and are referred to as L-CPV
(non-tracking), M-CPV (tracking in 1 dimension) and H-CPV (tracking
in 2 dimensions). In CPV modules the PV cell is not necessarily
encapsulated to such a degree that the PV cell and the materials in
contact with it are isolated from air, oxygen or moisture, and this
environmental condition is important to consider when producing a
radiation durable article for use in CPV.
[0085] Designing and fabricating the optical element involves both
selecting materials with appropriate index contrast, designing the
internal interface of the optical element, and fabricating the
optical element. To assure that the optical element has utility
during the lifetime of the PV module, requires that the selected
materials are radiation durable under the solar irradiances and
environmental conditions of oxygen and moisture for the
application. To define the radiation durability we must know the
radiation durability of the material, as represented by the induced
absorbance rate at the irradiance of the application, and the
desired lifetime of the PV module. The total dose of solar
radiation that will be imposed on the article is given by the
irradiance (in kW/m.sup.2) and the lifetime of the article. It must
be noted that photochemical degradation processes, such as
photochemical darkening (an increase in the optical absorbance/cm
at a particular wavelength lambda) can change dramatically with
changes in the solar irradiance, and also with changes in the level
of oxygen or moisture present in the environment of the
material.
[0086] Interface Design of the Optical Element
[0087] The conductor line optical element (CLOE) interface is
designed based on the index contrast of the 2 materials chosen, and
the following minimal CLOE interface defines target cusp angles,
cusp depths and throw lengths for the CLOE to functional
effectively. This minimal CLOE interface will be effective for the
application, but it does not restrict the interface from either
have larger or smaller cusp angles, depths or throw lengths. A less
than minimal CLOE interface design will still have some utility. At
the same time for some applications, such as in a CPV system where
converging light is incident on the illuminated surface of the CLOE
from a range of incident angles, one could decide to use a CLOE
interface in which the s chosen is many times wider than the actual
metallization lines on the PV cell, so that light incident from a
range of angles will still be swepted or diverted such that they
are not incident in the region of the PV cell obscured by the
metallization. These considerations also apply to use of CLOEs in
displays and LED lighting where the details of the illumination of
the CLOE will have one design the CLEO interface as appropriate for
sweeping light out of dark line regions or into bright line regions
as desired for the application.
Steps for Constructing a Minimal CLOE Interface:
[0088] For the case of a dark line CLOE, if material 1 has the
lower index of the pair of materials (n.sub.1/n.sub.2)<1), then
refer to FIG. 12A for the geometrical parameters. If material 1 has
the higher index of the pair of materials ((n.sub.1/n.sub.2)>1),
then refer to FIG. 12B for the geometrical parameters.
[0089] 1. Select a desired shadow width s.
[0090] 2. Pick a point on the first design map (FIG. 13A)
corresponding to a practical combination of relative refractive
index n.sub.r.ident.E n.sub.1/n.sub.2, maximum cusp height
h.sub.max and maximum cusp angle .quadrature..sub.max.
[0091] 3. Draw a polar coordinate system
(.quadrature.,.quadrature.) with an origin located a distance
h.sub.max below, and a distance s to the left, of the desired apex
point, and where the polar angle .quadrature. is to be measured
clockwise from the vertical line passing through the origin (which
will be denoted as the line-of-onset).
[0092] 4. Define the maximum polar angle
.quadrature..sub.max=tan.sup.-1(s/h.sub.max).
[0093] 5. Generate a curve .quadrature..sub.m(.quadrature.)
connecting the line-of-onset and apex point by plotting the
points:
.rho. m ( .alpha. ) = n r h max - s 2 + h max 2 n r cos .alpha. - 1
##EQU00001##
on the interval 0.ltoreq..quadrature..ltoreq..quadrature..sub.max,
which defines the refractive region. The intersection of this curve
with the line-of-onset defines the onset point where the tangent
slope of the curve is zero.
[0094] The resulting curve .quadrature..sub.m(.quadrature.) defines
the minimal CLOE interface with the following characteristics:
[0095] The interface is a portion of a conic-section of
eccentricity n.sub.r; i.e., an ellipse with downward-pointing cusp
for n.sub.r<1 or a hyperbola with upward-pointing cusp for
n.sub.r>1.
[0096] All light normally-incident on the minimal interface is
brought to a sharp focus at the origin.
[0097] The minimal interface represents the limiting case of all
possible generic CLOE interfaces that have the same shadow width s
and relative index n.sub.r.
[0098] The cusp angle of the minimal interface is
.quadrature..sub.max, the largest possible for any generic
interface.
[0099] The depth of the minimal interface over the shadow zone is
d.sub.min=|.quadrature..sub.m(0)-h.sub.max|, which can be read-off
from the second design map (FIG. 13B). This is the least depth of
any generic interface.
[0100] The reflection loss from the minimal interface will be
RL.sub.min (see the third design map, FIG. 13C), the least of any
generic interface.
[0101] The height h.sub.max of the minimal interface is the
greatest of any generic interface, such that the dark line half
width does not exceed s.
[0102] The steps for constructing a minimal CLOE interface for a
bright line optical element should be substantially analogous.
[0103] Materials Selection for Appropriate Index Contrast
[0104] Once the necessary light modulation width and periodicity
for the application are understood, the irradiance and lifetime
requirements in the application, the appropriate two materials to
use in designing the optical element and its internal interfacial
structure can be selected. The absolute value of the index
contrast, defined as |Log.sub.10(n.sub.1/n.sub.2)|, wants to be
large so as to produce a compact optical element, yet high contrast
can increase the reflection losses from the cusped regions as
possible. Yet at the same time, for the optical element to provide
sufficient lifetime it is necessary to choose very radiation
durable materials, which can lead to choosing a materials pair for
the optical element that has lower optical contrast, since in some
cases very high index materials also exhibit low radiation
durability and high induced absorbance rate.
[0105] Choosing one material to be a fluorine containing polymer
can be advantageous, since fluorine content is related to a
decrease in the index of refraction of the material, and therefore
serves to increase the index contrast of the chosen materials pair,
with out requiring one material to be of a very high index.
[0106] The materials may be chosen such that they do not have very
large index contrast, but instead so that they are less costly for
the application, while still exhibiting sufficient lifetime at the
application's irradiance level. An example of this would be using
ethylene backbone polymers in flat plate PV applications at 1
kW/m.sup.2 irradiance in which the module design precludes the
optical element being exposed to air or moisture during its
lifetime. This oxygen exposure avoidance, will reduce the degree of
photo-oxidative darkening of the materials, and enables the use of
less radiation durable materials than if they were used in an
oxygen containing environment. Radiation durability of materials in
Flat plate PV applications are reasonably well known, due to their
common use.
[0107] Even in the flat plate PV applications, many materials are
not radiation durable, even if they have adequate index contrast,
their lifetimes would be restricted to very short period.
[0108] In accordance with the present invention, preferred
materials are those that have an index contrast "c" as defined by
the relationship:
c=log.sub.10n.sub.R, where n.sub.R=(n.sub.1/n.sub.2)
[0109] wherein the absolute value of "c" lies within the range from
about 0.001 to about 0.17, such that
0.001<|c|<0.17.
[0110] More preferred are materials that have the absolute value of
"c" within the range from about 0.01 to about 0.05, such that
0.01<|c|<0.05.
[0111] The more preferred materials are indicated by underlined
values in the Table 1 labeled "D-line Index of Refraction and Index
Contrasts of materials 1 and 2. Index Contrast=Log 10 (n1/n2)" that
follows herein.
[0112] Materials Selection for Sufficient Lifetime in the Designed
Application and Irradiance
[0113] When looking at the CPV applications, where long lifetimes
at 5, 50 or 500 kW/m.sup.2 irradiances are desired, the total dose
of solar radiation delivered to the sample can become extremely
high. For example in 1 year, with AM1.5D solar radiation, a flat
plate (1 kW/m.sup.2) application will have a solar radiation dose
of approximately 9.3 GJ/m.sup.2/yr while at 50 Suns the total solar
radiation dose would be approximately 465.0 GJ/m.sup.2/yr, and at
1500 kW/m.sup.2 irradiance the total solar radiation dose would be
approximately 1395 GJ/m.sup.2/yr. The radiation durability of a
material may not be linear in dose, and may be strongly affected by
irradiance levels and environmental factors such as oxygen or
moisture. It is apparent that experimental knowledge of the
radiation durability is essential in materials selection for long
lifetime. Data at approximately 3.8 kW/m.sup.2 and 52 kW/m.sup.2
irradiance, which permits the determination of the induced
absorbance rate in materials that can be selected for use in a CLOE
is very important to the materials selection decisions. The
important radiation durability and lifetime considerations are that
the Irradiance times the desired lifetime represents the total
solar radiation dose that will be imposed on the materials during
their lifetime. The induced absorbance rate, which corresponds to
the highest rate of the increase in the optical absorbance of the
material, at some wavelength, represents photochemical darkening
events in the material. This induced absorbance rate times the
total dose expected over the CLOE's lifetime therefore gives one an
estimate of the total induced absorbance which is added to the
initial optical absorbance of the material prior to its use in
solar radiation. When the total optical absorbance of the material
becomes too large, the CLOE is degraded.
[0114] In accordance with the invention materials having an induced
absorbance rate .DELTA.Abs/Dose less than or equal to about 0.4 are
preferred. More preferred are materials that have an induced
absorbance rate .DELTA.Abs/Dose less than or equal to 0.2. The more
preferred materials are identified with underlined values in the
Table 2 "Induced Absorbance Rates of Materials Tested in Air at
Solar Irradiances Of Approximately 4 And 50 KW/m.sup.2" that
follows herein.
[0115] It should be noted that the presence of oxygen around a
material can increase its induced absorbance rate. In the mentioned
Table the induced absorbance rates are for materials tested in air.
Accordingly, various listed materials are inoperative when used in
an air environment (>=0.4). These inoperative (in air) materials
are indicated by an asterisk ("*") in the Table.
[0116] However, when these same materials are used for a flat plate
PV application, due to the encapsulation, these materials would
exhibit a lower induced absorbance rate. Therefore, various
materials identified in the table as an inoperative in air could be
operative in a flat plate PV application.
[0117] How the Optical Element is Made
[0118] The optical element can be manufactured by any of the
methods known in the art. In one embodiment of the invention the
optical element comprises a hard material and a soft material with
different indices of refraction giving adequate contrast. The hard
material can be glass or a transparent polymer with a high glass
transition temperature. The soft material can be a transparent
polymer with a lower glass transition temperature, or a
crosslinkable elastomer, or a liquid reactive oligomer. The hard
material determines the interfacial shape of the optical element.
It can be fabricated by standard methods such as compression and
injection molding at the appropriate temperatures. The soft
material can then be molded over the hard material at temperatures
that would not change the shape of the first material. In another
variation of the invention the soft material is a liquid oligomer
that can be poured over the hard material and cured in situ to
solid. In another variation the soft material can be applied from
solution using a solvent that does not interact with the first
material and the solvent then evaporated. The soft material can be
optionally crosslinked after the optical element is made. Typical
methods known in the art for crosslinking, such as the use of
thermal or photochemical initiators, can be used. In some
embodiments, copolymers can be used that are photocrosslinkable in
the absence of photoinitiators. Molds for compression or injection
molding can be made by methods known in the art such as mechanical
diamond turning and other microstructure creation methods such as
laser patterning of photosensitive materials. In most of these
methods a master is created first in a softer material such as
copper or a photopolymer, and then it is replicated using nickel
electro-deposition techniques well known in the art.
[0119] Combinations of CLOES with Secondary Optics
[0120] CLOEs can be used in CPV systems as an optical element
disposed between a secondary optic and a PV cell. Here the
plano-plano nature of the CLOE is very beneficial. FIG. 10 is a
stylized schematic representation of an integrated photovoltaic
cell assembly that includes a secondary optic, a PV cell, and an
optical element in accordance with the present invention.
[0121] The secondary optics are typically a secondary concentrator
to increase the optical concentration above that achieved by the
primary optical concentrator, an optical homogenizer which serves
to make the optical illumination of the PV cell more uniform, or a
combined secondary concentrator/homogenizer. It therefore is
possible combine the CLOE with the secondary optic and make a
single article that performs both the CLOE and secondary optic
functions.
[0122] The CLOE can also be integrated with the PV Cell and with
the PV cells submount if desired too further enable integration of
these elements, and simplify the assembly of the CPV module and
increase its performance and effectiveness.
[0123] CPV Module Discussion
[0124] A CPV module for low, medium or high concentration
incorporates a PV cell, with its submount and heat sink, with a
CLOE, any necessary secondary optics, the primary optics of the
system (e.g., a linear Fresnel Lens) and any structural elements
needed to position the components of the system and protect them
from the environment. Stylized schematic representations of low,
medium and high concentration CPV modules that include an optical
element in accordance with the present invention are illustrated in
FIGS. 9A through 9C, respectively.
[0125] CPV System Discussion
[0126] A CPV module must be mounted such that it is oriented
correctly with respect to the sun. In the case of a medium or high
concentration CPV system, it is also required to have a tracker,
which is a motorized system to enable the CPV module to be pointed
at the sun, as the sun traverses the sky during the day. The
tracker can be of a 1-axis motorized type, typical for an M-CPV
system, or a 2-axis tracker typically used for a H-CPV system. In
addition there are the required inverters to transform DC to AC
electricity and their associated wiring and electronics, and mounts
or bases to support the trackers and modules.
[0127] Flat Plate PV Discussion
[0128] FIG. 11 is a stylized schematic representation of a flat
plate PV apparatus that includes a photovoltaic cell with a front
side metallization, and optical element in accordance with the
present invention. The optical element 10/10' is encapsulated
between a front and a back sheet.
[0129] For Flat Plate PV, such as those using crystalline (single,
multi-crystalline or amorphous, or combined) silicon PV cells, or
using other PV cell materials such as CdTe, or CIGS, the PV module
is of a different type of construction that does not use primary
and secondary optics for focusing and homogenizing the light.
Instead 1 kW/m.sup.2 irradiance solar radiation is incident on the
PV cell. Flat Plate PV cells still in many cases use front side
metallization and have the same issue of obscuration. In these Flat
Plate PV modules, a CLOE can provide similar benefit by reducing
the negative impact of the front side obscuration. Also in many
cases, the PV cells are encapsulated to reduce any air or oxygen
exposure. The low oxygen and moisture environment in the region of
the PV cell in a Flat Plate system, can dramatically reduce the
induced absorbance rate of optical materials of utility in CLOEs,
and therefore permit longer useful lifetimes. The radiation
durability results presented in the examples are of materials in
air, and it is expected that in a low oxygen environment, typical
of a Flat Plate PV Module, many of these materials presented would
be applicable for CLOEs for Flat Plate PV cells and modules.
[0130] Displays
[0131] Displays are optical devices with addressable pixel units
which are spatially distributed and typically have a small region
around each pixel which is dark, i.e. is a region from which light
is not emitted. This is a common feature of liquid crystal displays
(LCDs), in which a back light unit, using fluorescent lamps or LED,
produces a uniform illumination of the back side of the LCD panel,
but due to the need to physically isolate adjacent pixels, there
are dark boundaries present on the side of the LCD panel opposite
to the back light unit. Similar phenomena arise in other pixel
based displays based on OLEDs or other light emitting displays.
CLOEs, can be designed to take the spatially modulated light,
exiting the pixel based display, and using an appropriately
designed CLOE, one can achieve a more spatially uniform
illumination on the side of the CLOE that is opposed to the LCD
display and its back light unit. This will effectively remove the
deleterious effect of the dark pixel boundaries on the display's
image.
[0132] LED Lighting
[0133] In the use of light emitting diodes (LEDs) for lighting, an
important issue is that the LEDs are exceedingly bright, spatially
localized sources of light that due to the small active, light
producing area of the LED to some degree approximate point sources
of light. In this case a CLOE can also be utilized to decrease the
strong spatial modulation of the light from the LED, to produce
less modulated light on the side of the CLOE which is opposite to
the LED.
EXAMPLES
Index of Refraction Methods & Results
[0134] Variable angle spectroscopic ellipsometry (VASE)
measurements were performed with a VUV-VASE.RTM. VU-302
manufactured by J.A. Woollam Co., Inc. which had a range from 0.69
to 8.55 eV (1800 to 145 nm), and employed MgF.sub.2 polarizers and
analyzers. The instrument had an MgF.sub.2 auto-retarder and was
fully nitrogen purged to avoid absorption of VUV light by ambient
oxygen and water vapor, which was important at wavelengths below
200 nm. Light from both the deuterium lamp and the xenon lamp
passed through a double-chamber Czerny-Turner type monochromator to
provide wavelength selection and stray-light rejection. The spot
diameter of light source on the surface of the sample was 2 mm.
Computer-controlled slit widths adjusted the bandwidth to insure
adequate spectral resolution of optical features in the data. These
included closely spaced interference oscillations, which arise in
very thick films. A photomultiplier tube was utilized for signal
detection in the ultraviolet. A stacked Si/InGaAs photodiode
detector was used for longer wavelengths. Ellipsometric
measurements were conducted using light incident at angles of
55.degree. to 80.degree.relative to normal on the front surface of
the sample, the back of which was roughened with coarse polishing
paper. The instrument measures the ellipsometric parameters .PSI.
and .DELTA., which are defined by Equation 1,
tan ( .PSI. ) i .DELTA. = R P R s ( 1 ) ##EQU00002##
where R.sub.P/R.sub.S is the complex ratio of the p and s-polarized
components of the reflected amplitudes. These parameters were
analyzed using the Fresnel equations in a computer-based modeling
technique to determine the optical constants. VUV-VASE.RTM. VU-302
measurements for this experiment were taken from wavelength range
145 nm to 1650 nm at multiple angles of incidence
(55.degree.-80.degree.. The ellipsometry data, taken from the film,
was fit to determine the polymer film roughness, thickness
non-uniformity, and complex refractive index. An optical model was
used to describe the film optical constants over the wide spectral
range. The film is modeled using initial optical constants. Then
the complete model was minimized by fitting the optical constants
on a point-by-point basis over the full spectral range in which the
data in each single wavelength was fit separately.
TABLE-US-00001 TABLE 1 D-line Index of Refraction and Index
Contrasts of materials 1 and 2. Index Contrast = Log10 (n1/n2).
Index Contrast = Material 2 Teflon .RTM. AF Teflon .RTM. Teflon
.RTM. Dyneon .RTM. Teflon .RTM. Log10(n.sub.1/n.sub.2) (n2) 1601
Example 2 Example 1 PFA FEP THV 220 Example 11 ETFE Material 1 (n1)
1.303 1.33 1.34 1.343 1.350 1.355 1.380 1.398 Teflon .RTM. AF 1601
1.303 0.000 -0.009 -0.012 -0.013 -0.015 -0.017 -0.025 -0.031
Example 2 1.33 0.009 0.000 -0.003 -0.004 -0.006 -0.008 -0.016
-0.022 Example 1 1.34 0.012 0.003 0.000 -0.001 -0.003 -0.005 -0.013
-0.018 Teflon .RTM. PFA 1.343 0.013 0.004 0.001 0.000 -0.002 -0.004
-0.012 -0.017 Teflon .RTM. FEP 1.350 0.015 0.006 0.003 0.002 0.000
-0.002 -0.010 -0.015 Dyneon .RTM. THV 220 1.355 0.017 0.008 0.005
0.004 0.002 0.000 -0.008 -0.014 Example 11 1.38 0.025 0.016 0.013
0.012 0.010 0.008 0.000 -0.006 Teflon .RTM. ETFE 1.398 0.031 0.022
0.018 0.017 0.015 0.014 0.006 0.000 Silicone RTV-615 1.406 0.033
0.024 0.021 0.020 0.018 0.016 0.008 0.002 Silicone XE14- 1.41 0.034
0.025 0.022 0.021 0.019 0.017 0.009 0.004 C1063 Amorphous SiO2 1.46
0.049 0.041 0.037 0.036 0.034 0.032 0.024 0.019 Tedlar .RTM. PVF
1.45 0.046 0.038 0.034 0.033 0.031 0.029 0.021 0.016 TR10AH9 Tedlar
.RTM. PVF 1.45 0.046 0.038 0.034 0.033 0.031 0.029 0.021 0.016
UT20BG3 PV5200 PVB 1.480 0.055 0.046 0.043 0.042 0.040 0.038 0.030
0.025 PV5300 Ionomer 1.487 0.057 0.048 0.045 0.044 0.042 0.040
0.032 0.027 PV1400 EVA 1.489 0.058 0.049 0.046 0.045 0.043 0.041
0.033 0.027 PMMA 1.489 0.058 0.049 0.046 0.045 0.043 0.041 0.033
0.027 Acrylite .RTM. FF 1.49 0.058 0.049 0.046 0.045 0.043 0.041
0.033 0.028 COC (Topaz) 1.498 0.061 0.052 0.048 0.047 0.045 0.044
0.036 0.030 Crystalline SiO2 1.543 0.073 0.065 0.061 0.060 0.058
0.056 0.048 0.043 PET 1.575 0.082 0.073 0.070 0.069 0.067 0.065
0.057 0.052 PC-Lexan 1.587 0.086 0.077 0.073 0.073 0.070 0.069
0.061 0.055 PS (677) 1.590 0.086 0.078 0.074 0.073 0.071 0.069
0.062 0.056 PEN 1.75 0.128 0.119 0.116 0.115 0.113 0.111 0.103
0.098 Silicone Tedlar .RTM. Tedlar .RTM. Index Contrast = Silicone
XE14- Amorphous PVF PVF PV5200 PV5300 PV1400 Log10(n1/n2) RTV-615
C1063 SiO2 TR10AH9 UT20BG3 PVB Ionomer EVA Material 1 (n1) 1.406
1.41 1.46 1.45 1.45 1.480 1.487 1.489 Teflon .RTM. AF 1601 -0.033
-0.034 -0.049 -0.046 -0.046 -0.055 -0.057 -0.058 Example 2 -0.024
-0.025 -0.041 -0.038 -0.038 -0.046 -0.048 -0.049 Example 1 -0.021
-0.022 -0.037 -0.034 -0.034 -0.043 -0.045 -0.046 Teflon .RTM. PFA
-0.020 -0.021 -0.036 -0.033 -0.033 -0.042 -0.044 -0.045 Teflon
.RTM. FEP -0.018 -0.019 -0.034 -0.031 -0.031 -0.040 -0.042 -0.043
Dyneon .RTM. THV 220 -0.016 -0.017 -0.032 -0.029 -0.029 -0.038
-0.040 -0.041 Example 11 -0.008 -0.009 -0.024 -0.021 -0.021 -0.030
-0.032 -0.033 Teflon .RTM. ETFE -0.002 -0.004 -0.019 -0.016 -0.016
-0.025 -0.027 -0.027 Silicone RTV-615 0.000 -0.001 -0.016 -0.013
-0.013 -0.022 -0.024 -0.025 Silicone XE14-C1063 0.001 0.000 -0.015
-0.012 -0.012 -0.021 -0.023 -0.024 Amorphous SiO2 0.016 0.015 0.000
0.003 0.003 -0.006 -0.008 -0.009 Tedlar .RTM. PVF 0.013 0.012 0.003
0.000 0.000 -0.009 -0.011 -0.012 TR10AH9 Tedlar .RTM. PVF 0.013
0.012 0.003 0.000 0.000 -0.009 -0.011 -0.012 UT20BG3 PV5200 PVB
0.022 0.021 0.006 0.009 0.009 0.000 -0.002 -0.003 PV5300 Ionomer
0.024 0.023 0.008 0.011 0.011 0.002 0.000 -0.001 PV1400 EVA 0.025
0.024 0.009 0.012 0.012 0.003 0.001 0.000 PMMA 0.025 0.024 0.009
0.012 0.012 0.003 0.001 0.000 Acrylite .RTM. FF 0.025 0.024 0.009
0.012 0.012 0.003 0.001 0.000 COC (Topaz) 0.028 0.026 0.011 0.014
0.014 0.005 0.003 0.003 Crystalline SiO2 0.040 0.039 0.024 0.027
0.027 0.018 0.016 0.015 PET 0.049 0.048 0.033 0.036 0.036 0.027
0.025 0.024 PC-Lexan 0.053 0.051 0.036 0.039 0.039 0.030 0.028
0.028 PS (677) 0.053 0.052 0.037 0.040 0.040 0.031 0.029 0.029 PEN
0.095 0.094 0.079 0.082 0.082 0.073 0.071 0.070 Index Contrast =
COC Crystalline Log10(n1/n2) PMMA Acrylite .RTM. FF (Topaz) SiO2
PET PC-Lexan PS (677) PEN Material 1 (n1) 1.489 1.49 1.498 1.543
1.575 1.587 1.590 1.75 Teflon .RTM. AF 1601 -0.058 -0.058 -0.061
-0.073 -0.082 -0.086 -0.086 -0.128 Example 2 -0.049 -0.049 -0.052
-0.065 -0.073 -0.077 -0.078 -0.119 Example 1 -0.046 -0.046 -0.048
-0.061 -0.070 -0.073 -0.074 -0.116 Teflon .RTM. PFA -0.045 -0.045
-0.047 -0.060 -0.069 -0.073 -0.073 -0.115 Teflon .RTM. FEP -0.043
-0.043 -0.045 -0.058 -0.067 -0.070 -0.071 -0.113 Dyneon .RTM. THV
220 -0.041 -0.041 -0.044 -0.056 -0.065 -0.069 -0.069 -0.111 Example
11 -0.033 -0.033 -0.036 -0.048 -0.057 -0.061 -0.062 -0.103 Teflon
.RTM. ETFE -0.027 -0.028 -0.030 -0.043 -0.052 -0.055 -0.056 -0.098
Silicone RTV-615 -0.025 -0.025 -0.028 -0.040 -0.049 -0.053 -0.053
-0.095 Silicone XE14- -0.024 -0.024 -0.026 -0.039 -0.048 -0.051
-0.052 -0.094 C1063 Amorphous SiO2 -0.009 -0.009 -0.011 -0.024
-0.033 -0.036 -0.037 -0.079 Tedlar .RTM. PVF -0.012 -0.012 -0.014
-0.027 -0.036 -0.039 -0.040 -0.082 TR10AH9 Tedlar .RTM. PVF -0.012
-0.012 -0.014 -0.027 -0.036 -0.039 -0.040 -0.082 UT20BG3 PV5200 PVB
-0.003 -0.003 -0.005 -0.018 -0.027 -0.030 -0.031 -0.073 PV5300
Ionomer -0.001 -0.001 -0.003 -0.016 -0.025 -0.028 -0.029 -0.071
PV1400 EVA 0.000 0.000 -0.003 -0.015 -0.024 -0.028 -0.029 -0.070
PMMA 0.000 0.000 -0.003 -0.015 -0.024 -0.028 -0.029 -0.070 Acrylite
.RTM. FF 0.000 0.000 -0.002 -0.015 -0.024 -0.027 -0.028 -0.070 COC
(Topaz) 0.003 0.002 0.000 -0.013 -0.022 -0.025 -0.026 -0.068
Crystalline SiO2 0.015 0.015 0.013 0.000 -0.009 -0.012 -0.013
-0.055 PET 0.024 0.024 0.022 0.009 0.000 -0.003 -0.004 -0.046
PC-Lexan 0.028 0.027 0.025 0.012 0.003 0.000 -0.001 -0.042 PS (677)
0.029 0.028 0.026 0.013 0.004 0.001 0.000 -0.042 PEN 0.070 0.070
0.068 0.055 0.046 0.042 0.042 0.000
[0135] Radiation Durability Methods & Results
Solar Radiation Exposure Method
[0136] The following describes the solar simulated irradiation
durability set up and procedures used to expose materials to
simulated solar light to enable the evaluation of the effect of
full spectrum simulated solar radiation on materials.
[0137] To simulate solar radiation exposure of samples used were a
Newport Corporation, (Corporate Headquarters, 1791 Deere Avenue,
Irvine Calif. 92606), Solar Simulator, (Model #92190-100), with a
Newport Power Supply, (Model #69922), that sends a programmed power
output to a Newport Digital Exposure Control unit, (Model #68945),
that was coupled with a fiber optic feed back sensor, located at
the beam exit, to digitally control the light flux. This permitted
the solar simulator to operate in a programmed control range that
delivered a constant irradiance to the samples over the duration of
the test.
[0138] The Newport Solar Simulator used a 1600 watt Xenon lamp in
combination with integrated internal optics, including AM 0 and
AM1.5 optical filters, to deliver a diverging beam of simulated
solar spectral irradiance to the sample area. To measure the power
output, at the sample level a Newport Power Meter, (Model #1918-C),
connected to a Newport thermopile detector, (Model #818-250-25),
located in the optical beam path, was used.
[0139] Radiation durability testing was done at uniform irradiance
of approximately 3.8 KW/m.sup.2. This was at a working distance of
8.3 cm from the exit window of the simulator in an exposure area of
15.times.15 cm. This working area allowed for the simultaneous
testing of multiple samples. Typical sample size was 2.5.times.4
cm; sample thickness varied from 0.025 to 2.5 mm. The total
exposure dose in GJ/m.sup.2 was calculated from the irradiance in
kW/m.sup.2 times the exposure time. The beam irradiance was
measured using a Newport 25 watt thermopile type detector, (Model
#(818-25-12),). During irradiation exposures, temperature and
relative humidity were not controlled, they are typical of an air
conditioned laboratory. Sample temperature rose from room
temperature to typically 50.degree. C. as samples were exposed to
the simulated solar light.
[0140] Radiation Durability was also done at uniform irradiances of
48 kW/m.sup.2 by adding a Newport 13.times. concentrator lens
assembly, (Model #SP81030-DIV) to the exit window of the Newport
Solar Simulator. The assembly mounted onto the diverging solar
simulator producing a 2.5.times.2.5 cm working area at a distance
of 8.5 cm from the final condensing lens which enabled testing
samples up to 2.5.times.0.5 cm in size. This beam irradiance was
measured by using a Newport 250 watt fan cooled thermopile type
detector, (Model #818-250-25), with a 0.6.times.0.6 cm aperture
plate attached. Also, during irradiation, temperature and relative
humidity are not controlled but are typical of an air conditioned
laboratory. Sample temperature rises from room temperature to
typically 50.degree. C. as samples are exposed to the simulated
solar light.
Center Mount Absorbance Method
[0141] The optical absorbance of free standing films and films on
high purity fused silica substrates was determined by the center
mount absorbance method over the entire 200-2500 nm wavelength
range using a Varian Cary 5000 UV-Vis-NIR spectrophotometer with an
accessory integrating sphere (Varian DRA-2500). A clip-style
variable angle center mount sample holder is used for the
absorbance measurement for films and film on glass translucent
samples. The measured value of absorbance was divided by the film
thickness to obtain a value of optical absorbance per cm (base
10).
A / cm = ( - log T film ) / t ( 2 ) A / cm = log 10 [ T substrate /
T film ] t film ( 3 ) ##EQU00003##
Where A is the base 10 optical absorbance per cm, T is the
transmission of film, and t is the thickness of film (cm). The
calculation of optical absorbance assumed that the free standing
film was of homogenous composition and uniform thickness. For film
on glass samples, the calculation of optical absorbance assumed
that the transmission (T) of the glass substrate is 1. Transmission
based measurements also required that the film thickness of the
sample on the substrate be optimized for the dynamic range of the
technique so that the transmittance of the film falls in the range
from 3 to 90%. If the transmittance falls much below 1%, the
accuracy of the measurement was severely degraded, and erroneous
results appear.
[0142] The center mount measurement was conducted under the
following conditions: The external DRA-2500 was installed into the
spectrophotometer and aligned. UV-Vis-NIR spectra were, in general,
acquired in the region of 200-2500 nm using appropriate baseline
correction (zero/baseline for % T and absorbance correction for
spectral only). Indicative instrumental parameters were as follows:
spectral bandwidth (SBW): 4 nm (UV/Vis), 16 nm (NIR); averaging
time: 0.4 sec; data interval: 2 nm; double beam mode using full
slit height for % T and absorbance, a small spot kit (SSK) was used
for the center mount absorbance data.
[0143] As in all experimental measurements, the accuracy of the
measured values was a function of the sample and measurement
apparatus. The inherent sensitivity of spectral transmission and
absorbance measurements is affected by the optical path length of
the sample, and the transmission drop that occurs as light
transmits through the sample. As the transmission decreased, the
accuracy of absorbance measurement decreased. A transmission
difference of -0.1% is near the limit of the measurement
method.
Induced Absorbance Rate: Average .DELTA.Abs/cm per GJ/m.sup.2 Dose
Calculation
[0144] The induced absorbance rate, or Average .DELTA.Abs/cm per
GJ/m.sup.2 Dose, was calculated by
Average Abs cm per GJ m 2 Dose = Abs f ( .lamda. ) / cm - Abs i (
.lamda. ) / cm Dose total Equation ( 4 ) ##EQU00004##
[0145] Where Abs.sub.f is the finial spectral optical absorbance,
Abs.sub.i is the initial spectral optical absorbance and
Dose.sub.total is the total dose of the sample received.
[0146] It is important to develop a useful metric of photochemical
processes such as photobleaching or photodarkening in testing CPV
materials. One desirable radiation durability metric is the change
in the spectral optical absorbance (.DELTA.Abs/cm (.lamda.)) for an
average of full spectrum solar radiation dose (in GJ/m.sup.2) since
this allows us to observe and study the sources of photochemical
changes which arise over the exposure time. This is called the
average .DELTA.Abs/cm per GJ/m.sup.2 dose (or induced absorbance
rate), and this metric allows tracking of the rates of
photochemical processes including photochemical bleaching and
darkening of both intrinsic and extrinsic components of the
material and is scaled in units of 1 GJ/m.sup.2 dose.
[0147] Combining insights derived from the Induced Absorbance Rate,
with experiments run at different irradiance levels (such as 3.8
kW/m.sup.2 and 48.2 kW/m.sup.2), will help to define the best
material sets and understand the mechanisms which are related to
the lifetime improvement.
[0148] The Average .DELTA.Abs/cm per GJ/m.sup.2 Dose was measured
as a function of wavelength and in the table report the value of
this induced absorbance rate for a particular wavelength where it
is the largest positive value observed at a particular irradiance.
Positive values of the induced absorbance rate correspond to
Photodarkening, i.e. increasing optical absorbance, whereas
negative values of the induced absorbance rate correspond to
Photobleaching. The induced absorbance rate was used as indicative
of solar radiation induced photodegradation of the material, which
limits the useful lifetime of the material in the optical element
due to the continuing increase in the material's optical
absorbance.
TABLE-US-00002 TABLE 2 Induced Absorbance Rates of Materials Tested
in Air at Solar Irradiances Of Approximately 4 And 50 KW/m.sup.2 4
Sun 4 Sun 4 Sun 4 Sun 50 Sun 50 50 Sun 50 Sun Irradiance Total
.DELTA.Abs/Dose At .lamda. Irradiance SunTotal .DELTA.Abs/Dose At
.lamda. Material (kW/m.sup.2) Dose (GJ/m.sup.2) (Abs/cm/(GJ/m2))
(nm) (kW/m.sup.2) Dose (GJ/m.sup.2) (Abs/cm/(GJ/m2)) (nm) Teflon
PFA (5 mil) -- 52.0 158.0 0.008 222 Teflon .RTM. FEP 200A 3.8 42.4
0 -- Teflon .RTM. FEP 500A 3.8 42.4 0 52.0 158.0 0.014 222 Teflon
.RTM. ETFE 3.8 42.4 0 -- 200LZ Teflon .RTM. ETFE 3.8 42.4 0 52.0
158.0 0 500LZ Example 2 3.8 37.4 0.076 304 52.0 158.0 0.021 308
Example 1 3.8 37.4 0 52.0 158.0 0.175 234 Example 11 3.8 37.4 0
52.0 158.0 0 Tedlar .RTM. TUT20BG3 3.8 37.4 0 -- Tedlar
.RTM.TR10AH9 3.7 27.4 0 51.7 79.8 0.013 312 Silicone XE14- 3.8 37.4
0.033 237 52.0 78.2 0.055 230 C1063 Melinex XST 6578 3.7 27.4 0.085
396 -- RTV615 Silicone 3.8 37.4 0.172 220 52.0 158.0 0.021 228
DuPont .TM. PV 5200 3.9 29.8 0.474 266 -- (PVB) * Korad .RTM. Film
05005 * 3.8 37.4 0.491 244 -- DuPont .TM. Elvax .RTM. 3.8 32.4
0.807 242 -- PV1400 * DuPont .TM. PV 5300 * 3.8 26.9 1.098 266 --
Melinex .RTM. ST504 * 3.7 27.4 1.72 332 -- Mylar .RTM. 200 DM * 4.1
10.0 6.78 328 52.0 34.1 6.39 336 * Inoperative for use in an oxygen
containing environment
[0149] Classes of Materials and Obtaining these Commercial
Materials
[0150] Suitable hard materials for forming the optical elements
include crystalline SiO.sub.2 and various glasses, for example
soda-lime glass, borosilicate glass and flint glass. Suitable
glasses are commonly commercially available.
[0151] Suitable hard materials also include transparent polymers
and copolymers with a glass transition temperature above
100.degree. C. and a transparency greater than 90%, for example,
polymethyl methacrylate, polycarbonate, and cyclic olefin
copolymers. Such transparent polymers and copolymers are commonly
commercially available.
[0152] Suitable soft material for forming the optical elements
includes transparent polymers and copolymers with a glass
transition temperature below 100.degree. C. and a transparency
greater than 90%. Suitable soft polymers and copolymers include
polydimethylsiloxane, butyl acrylate copolymers, and ethylene
copolymers with vinyl acetate or (meth)acrylic acid.
[0153] Suitable soft materials also include crosslinkable
elastomers such as polybutadiene, transparent FKM and FFKM
fluoroelastomers, and silicone rubbers. These elastomers can be
crosslinked by heating or through the use of photoinitiators such
as benzyl dimethyl ketal, benzophenone or triphenyl phosphine
oxide, using techniques that are known in the art.
[0154] Suitable soft materials also include liquid reactive
oligomers such as polyethyleneglycol diacrylate, ethoxylated and
propoxylated trimethylolpropane triacrylates, and ethoxylated
pentaerythritol tetraacrylate. These oligomers can be crosslinked
by free radical initiators such as organic peroxides and
photoinitiators using techniques well known in the art.
[0155] In some embodiments, the soft material is a copolymer
comprising at least one monomer selected from the group consisting
of EVE, 8-SAVE and 8-CNVE and at least one monomer selected from
the group consisting of E, TFE, VF2, PDD, PPVE, PMVE, PEVE, and
EVEOCN. These copolymers are typically tacky as prepared and
soluble in some solvents, but become harder and less soluble upon
exposure to UV radiation, even in the absence of a photoinitiator.
Longer exposure times and/or higher intensity UV radiation result
in more cross-linking and more pronounced changes in the copolymer
properties. Examples of the preparation and photocrosslinking of
representative copolymers are given below:
Synthesis of Non-Commercial Materials
Example 1
Preparation and Photocrosslinking of poly(EVE/TFE)
[0156] A 1 liter autoclave was loaded with 200 ml of EVE, heated to
30.degree. C. with stirring, pressured with 100 psi N.sub.2, and
vented three times. The autoclave was then pressured to 30 psi with
TFE and vented, four times. The autoclave was pressured to 50 psi
with TFE. Using a chilled line, 0.2 ml of -0.2 M DP in Vertrel XF
was injected. After stirring for 1 hr at ambient temperature,
additional 0.2 M DP was injected at a rate of .about.0.01 ml/min
until 15 g of TFE had been adsorbed, while holding TFE pressure
constant at 50 psi. A total of 6.72 ml of DP was injected over 623
min. The product mixture was recovered as a hazy fluid, with the
consistency of motor oil. Excess EVE was distilled off under
vacuum, eventually bringing the heating mantle 157.degree. C. while
pulling a vacuum of -520 mm. This gave 40.2 g of slightly tacky
gum. The gum had a Tg of -30.degree. C. (DSC, 10.degree. C./min,
N.sub.2, second heat). NMR analysis found the polymer to be 34.4
mole % EVE and 65.6 mole % tetrafluoroethylene. A 0.1 g sample of
residue readily dissolved in 1 g of hexafluorobenzene, making a
clear solution with a few undissolved particulates. Inherent
viscosity in hexafluorobenzene was 0.07 dL/g.
[0157] After 68 hr of exposure 1 "under a Rayonet Photochemical
Reactor bulb, a sample of poly(EVE/TFE) turned from a soft gum to a
brittle film. Rolling a 0.0335 g piece of film with 0.5 g of
hexafluorobenzene for 3 hr caused the film to gain 11% in weight. A
curled piece of film maintained its shape for 2 hr in a 225.degree.
C. oven, a major change from the soft, gummy starting polymer prior
to UV exposure. Exposure for 60 min at 11.5 millwatts/cm.sup.2 UV
intensity made a sample of poly(EVE/TFE) smooth to the touch. The
polymer sprang back when indented with a fingernail and formed a
gel when mixed with hexafluorobenzene.
[0158] The index of refraction at D-line was 1.34 and the induced
absorbance rate was less than or equal to 0 Abs/cm/(GJ/m.sup.2)) at
3.8 kW/m.sup.2 and was 0.175 at a wavelength of 234 nm at an
irradiance of 52 kW/m.sup.2.
Example 2
Preparation and Photocrosslinking of Poly(TFE/PMVE/PEVE/8-SAVE)
[0159] A 1 liter autoclave was charged with 450 ml of distilled
water, 0.8 g of ammonium persulfate, 3 g of
C.sub.8F.sub.17COONH.sub.4, and 20 g of
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2SO.sub.2N.sub.3
(8-SAVE). The autoclave was sealed, evacuated and further loaded
with 36 g of CF.sub.2.dbd.CFOCF.sub.2CF.sub.3 (PEVE), 83 g
CF.sub.2.dbd.CFOCF.sub.3 (PMVE), and 45 g of CF.sub.2.dbd.CF.sub.2
(TFE). The autoclave was heated slowly to 70.degree. C., and then
stirred for 8 hr at 70.degree. C., while maintaining pressure from
about 230-250 psi by the periodic addition of TFE:PMVE:PEVE in a
roughly 1 g to 0.4 g to 0.25 g ratio. This gave an opalescent blue
emulsion, with a small mass of precipitated polymer on top. The
precipitated polymer was removed by filtering through cheesecloth
packed in the neck of a filter funnel, giving 742 g of
filtrate.
[0160] About 670 g of this filtrate were frozen and thawed. The
resulting damp mass was broken into two batches, with each batch
being washed in a Waring blender twice with 1000 ml of water, twice
with 600 ml of methanol, and twice with 750 ml of acetone. Sucking
the washed product dry in a Buchner filter gave springy, elastic
cakes, 166 g from the first batch and 112 grams from the second
batch.
[0161] The polymer analysed for 66.6 mole % TFE, 22.8 mole % PMVE,
9.2 mole % PEVE, and 1.4 mole % 8-SAVE by .sup.19F NMR. The polymer
had a Tg of 6.5.degree. C. (DSC, 10.degree. C./min, N.sub.2, second
heat).
[0162] Rolling a 0.1 g sample of poly(TFE/PMVE/PEVE/8-SAVE) with 3
ml of Novec HFE-7500 gave a hazy solution, which was spotted on a
glass microscope slide and air-dried to a colorless film. The
microscope slide, while in a quartz box under N.sub.2, was
irradiated for 17 hr with a Rayonet Photochemical Reactor bulb. The
irradiated poly(TFE/PMVE/PEVE/8-SAVE) did not redissolve in Novec
HFE-7500.
[0163] The index of refraction at D-line was 1.33 and the induced
absorbance rate was 0.076 Abs/cm/(GJ/m.sup.2)) at 3.8 kW/m.sup.2
and was 0.021 at a wavelength of 308 nm at an irradiance of 52
kW/m.sup.2.
Example 3
Preparation and Photocrosslinking of poly(EVE/E)
[0164] A 210 ml autoclave was chilled to about -20.degree. C. and
42 ml of EVE and 10 ml of .about.0.19 M DP initiator in Vertrel XF
were added. The autoclave was evacuated and 3 g of ethylene were
added. While shaking overnight, the pressure inside the autoclave
reached a maximum of 84 psi at 20.degree. C. after 45 min and
decreased to 18 psi at 26.5.degree. C. at the end of the run 921
min later. The resulting hazy fluid was transferred to a
Teflon.RTM.-lined tray and allowed to evaporate first at ambient
and then overnight in a 75.degree. C. oven, at which point the
clear, tacky residue weighed 22.4 g. The residue still weighed 22.4
g after another 24 hr in the 75.degree. C. oven. The gum had a Tg
of -36.degree. C. (DSC, 10.degree. C./min, N.sub.2, second heat).
Combustion analysis found 29.92% C and 1.64% H, versus 29.70% C and
1.65% H calculated for a polymer that is 47.6 mole % EVE and 52.4
mole % ethylene. A 0.1 g sample of residue readily dissolved in 1
ml of 2-heptanone, making a clear solution.
[0165] Exposure of a sample of poly(EVE/E) to 0.2
milliwatts/cm.sup.2 UV intensity transformed it from a tacky
glue-like material that was readily soluble in 2-heptanone to a
non-tacky, modestly elastomeric polymer that swelled but did not
dissolve in 2-heptanone. Exposure for 60 min at 11.5
millwatts/cm.sup.2 UV intensity made the polymer silky smooth to
the touch. The polymer sprang back when indented with a fingernail
and formed a gel when mixed with 2-heptanone.
Example 4
Preparation and Photocrosslinking of Poly(EVE/VF2)
[0166] A 240 ml autoclave was chilled to about -20.degree. C., and
42.2 ml of EVE dissolved in 20 ml of Vertrel XF and 25 ml of
.about.0.05 M DP initiator in Vertrel XF were added. The autoclave
was evacuated and 13 g of vinylidene fluoride was added. Shaking
overnight, the pressure inside the autoclave reached a maximum of
103 psi at 24.degree. C. after 70 min and decreased to 5 psi at
25.4.degree. C. at the end of the run 1090 min later. This gave a
viscous, clear, water-white solution. Drying a 0.9637 g sample of
this solution, first under a flow of nitrogen, and then overnight
in a 75.degree. C. oven gave 0.6703 g of tacky gum.
[0167] After exposure for 60 min at 11.5 millwatts/cm.sup.2 UV
intensity, a sample of poly(EVE/VF2) had no tack, sprang back when
indented with a fingernail, and formed a gel when mixed with
2-heptanone.
Example 5
Preparation and Photocrosslinking of Poly(EVE/TFE/PDD)
[0168] A 210 ml autoclave was chilled to about -20.degree. C., and
4 g of EVE dissolved in 50 ml of Vertrel XF, 14.2 ml of PDD, and 10
ml of .about.0.17 M DP initiator in Vertrel XF were added. The
autoclave was evacuated and 10 g of tetrafluoroethylene was added.
Shaking overnight, the pressure inside the autoclave reached a
maximum of 57 psi at 33.6.degree. C. after 66 min, and decreased to
17 psi at 33.3.degree. C. at the end of the run 990 min later. This
gave a highly viscous solution that barely flowed. Drying under a
N.sub.2 flow for 43 hr under pump vacuum, and for 24 hr in a
75-52.degree. C. vacuum oven, gave 32.55 g of polymer that had an
inherent viscosity of 0.370 dL/g in hexafluorobenzene. Composition
by fluorine NMR was 1.2 mole % EVE, 53.7 mole % TFE, and 45.1 mole
% PDD.
[0169] After exposure under a 1 kW deep UV short arc lithographic
lamp for 60 min, a sample of poly(EVE/TFE/PDD) was found to have no
tack, to be still stiffer, and to form a gel that retained the
shape of the starting film when mixed with Fluorinert FC-40.
Example 6
Preparation and Photocrosslinking of Poly(EVE/PDD)
[0170] A small sample vial equipped with serum cap and magnetic
stir bar was loaded with 1 ml of PDD and 2 ml of EVE. The vial was
flushed with N.sub.2, and 1 ml of .about.0.17M DP in Vertrel XF was
injected. Three days later, a second ml of .about.0.17M DP was
injected. On the sixth day, the reaction mixture was added to
.about.30 ml of methanol. The resulting precipitate was filtered,
sucked dry in the filter, and further dried for 16 hr under pump
vacuum to give 0.71 g of product. Combustion analysis found 24.88%
C, versus 25.24% C calculated for 1:1 poly(EVE:PDD).
[0171] After a sample of poly(EVE/PDD) was irradiated overnight at
about 0.2 milliwatts/cm.sup.2 UV intensity, it was no longer
soluble in perfluorooctane.
Example 7
Preparation and Photocrosslinking of Poly(EVE/TFE/PPVE)
[0172] A 400 ml autoclave was chilled to about -20.degree. C., and
10 g of EVE dissolved in 100 ml of Vertrel XF, and 10 ml of
.about.0.2 M DP initiator in Vertrel XF were added. The autoclave
was evacuated, and 50 g of tetrafluoroethylene was added. Shaking
overnight, the pressure inside the autoclave reached a maximum of
84 psi at 6.5.degree. C. after 22 min, and decreased to 0 psi at
20.9.degree. C. at the end of the run 1043 min later. The damp
white solid was transferred to a vacuum filter, rinsed in the
filter with Vertrel XF, sucked dry in the filter, and further dried
overnight in a 130.degree. C. vacuum oven, giving 53.2 g of
product.
[0173] A 1 g sample of poly(EVE/TFE/PPVE) was placed between two
Kapton.RTM. sheets and heated for ten min between the platens of a
320.degree. C. press before applying a force of 20,000 pounds for
22 min. This gave a hazy film .about.3'' in diameter and 4 to 5
mils thick. The film was cut in half and one half placed in a
quartz box under N.sub.2 where it was irradiated for about 65 hr at
about 0.2 milliwatts/cm.sup.2 UV intensity. Dynamic mechanical
analysis of the exposed and unexposed halves of the polymer film at
245.degree. C. found the exposed half of the film to be stiffer,
with a higher modulus (34 MPa) than the unexposed half of the film
(22 MPa).
Example 8
Preparation and Photocrosslinking of Poly(8-CNVE/PDD/TFE)
[0174] An autoclave was chilled to about -20.degree. C., and 4 g of
8-CNVE dissolved in 20 ml of Vertrel XF, 14.2 ml of PDD, and 5 ml
of .about.0.17 M DP initiator in Vertrel XF were added. The
autoclave was evacuated, and 7 g of tetrafluoroethylene were added.
Shaking overnight, the pressure inside the autoclave reached a
maximum of 110 psi at 17.3.degree. C. after 59 min, and decreased
to 49 psi at 34.1.degree. C. at the end of the run, 1000 min later.
This gave a colorless gel. Drying under a N.sub.2 flow and then for
43 hr under pump vacuum gave 27.8 g of polymer that had an inherent
viscosity of 0.476 dL/g in hexafluorobenzene. .sup.19F NMR was
consistent with a polymer composition of 2.3 mole % 8-CNVE, 42.3
mole % TFE, and 53.4 mole % PDD; 2 mole % of unreacted 8-CNVE
monomer was also detected. Tg was 106.degree. C. (second heat,
10.degree. C./min, N.sub.2). The polymer made viscous, clear
solutions when dissolved at 0.1 g/1 g hexafluorobenzene and 0.1 g/2
g of Fluorinert FC-40.
[0175] Rolling a 0.1 g sample of poly(8-CNVE/PDD/TFE) with 1 g of
Fluorinert FC-40 gave an extremely viscous solution which was
spotted on a glass microscope slide and air-dried to a film. The
microscope slide, while in a quartz box under N.sub.2, was
irradiated for 71.5 hr with about -0.2 milliwatts/cm.sup.2 UV
intensity. The recovered film sample of poly(8-CNVE/PDD/TFE) gave a
swollen gel in Fluorinert FC-40.
Example 9
Preparation and Photocrosslinking of Poly(8-CNVE/EVEOCN/PDD)
[0176] A small sample vial equipped with serum cap and magnetic
stir bar was loaded with 2 ml 8-CNVE, 0.2 ml EVEOCN, and 1 ml of
PDD while chilling on dry ice. The vial was flushed with N.sub.2,
and 0.5 ml of .about.0.2 M DP in Vertrel XF was injected. The vial
was allowed to warm to room temperature with magnetic stirring. The
next morning, a second 0.05 ml of .about.0.17M DP was injected. On
the following day, the viscous reaction mixture was blown down with
N.sub.2, giving 4.1 g of white solid that had an inherent viscosity
of 0.108 dL/g in Novec HFE-7500. .sup.19F NMR was consistent with a
polymer composition of 22.2 mole % 8-CNVE, 4.4 mole % EVEOCN, and
63.4 mole % PDD; 7.6 mole % of unreacted 8-CNVE monomer and 2.4
mole % of unreacted EVEOCN monomer were also detected. Tg was
115.degree. C. (second heat, 10.degree. C./min, N.sub.2). The
polymer made clear solutions when dissolved at 0.1 g/1 g of either
hexafluorobenzene or Novec HFE-7500.
[0177] Rolling a 0.1 g sample of poly(8-CNVE/EVEOCN/PDD) with 1 g
of Novec HFE-7500 gave a clear solution, which was spotted on a
glass microscope slide and air-dried to a film. The microscope
slide, while in a quartz box under N.sub.2, was irradiated using a
Rayonet Photochemical Reactor bulb. After 70.5 hr, a 0.021 g sample
of film fragments showed no sign of solution or swelling with 1 g
of Novec HFE-7500.
Example 10
Very Fast Photocrosslinking of Poly(EVE/E), Poly(EVE/VF2), and
Poly(EVE/TFE)
[0178] Lumps of poly(EVE/E), poly(EVE/VF2), and poly(EVE/TFE)
weighing from -0.2 to 0.4 g were spread on glass microscope slides
by heating for 1 hr in a 120.degree. C. oven.
[0179] The thick films were exposed to very high intensity UV light
using a PulseForge.TM. flash lamp (NovaCentrix, Austin, Tex.). The
exposures consisted of sixteen 80 microsecond exposures at
increasingly high intensity, followed by 20 to 40 additional
exposures at the highest intensity, each exposure lasting for 80
microseconds. After a total exposure time of 0.028 sec, the
poly(EVE/E) broke into fragments (rather than dissolving) when
rolled in 2-heptanone. After a total exposure time of 0.044 sec,
the poly(VF2/EVE) swelled in 2-heptanone with a 92% weight gain
when rolled with 2-heptanone. After a total exposure time of 0.028
sec, the poly(EVE/TFE) became a soft viscous gel rather than
dissolving when rolled with hexafluorobenzene.
Example 11
Preparation of Photocrosslinked Viton.RTM. Films
[0180] Viton.RTM. GAL200-S (DuPont) was dissolved in propyl acetate
to make a 9.96 weight % solution. To 25 g of this solution were
added 0.125 g of triallyl isocyanurate (TAIC, Aldrich) and 0.125 g
of photoinitiator Irgacure.RTM. 651 (Ciba). The ingredients were
stirred until a homogeneous solution was obtained. The solution was
then filtered through a 0.45 micron PTFE syringe filter and some
solvent evaporated using a rotary evaporator at room temperature to
reduce the volume by 50% yielding a viscous liquid. Films were cast
on microscope slides using this solution and, after air drying,
they were crosslinked at 60.degree. C. under nitrogen atmosphere
using a Blak-Ray.RTM. B-100AP lamp (UVP, LLC. Upland, Calif.) for
15 minutes at 24 mW/cm.sup.2 at 365 nm.
[0181] The index of refraction at D-line was 1.38 and the induced
absorbance rate was less than or equal to 0 Abs/cm/(GJ/m.sup.2)) at
3.8 kW/m.sup.2 and was less than or equal to 0 at an irradiance of
52 kW/m.sup.2.
Example 12
[0182] A ray tracing model of a plano-plano structure using a
lenticular array has been created with the cusps pointing up,
toward the light source, and toward the higher index material. The
repeat period is 100 micro meters, the index of refraction of the
top layer is 1.506, and the index of refraction of the bottom layer
is 1.34. The distance from the cusp apex point to the viewing plane
is 50 micro meters. FIG. 14A is a 3-dimensional rendering of this
structure. FIG. 14B shows a portion of the cross section of this
structure and the intensity profile created by the ray tracing
program, TracePro6.0.RTM.. The intensity profile is normalized by
the intensity that would have been seen in the absence of the
plano-plano structure. A merit function has been created as a
measure of the integrated increase in intensity in the bright
areas. In this case the merit function is 21.28% from the ray trace
data compared to 21.95% from an optimistic design estimate. The
parameter s is half the dark space length in the intensity profile.
This measures to be 9 micro meters in this example.
Example 13
[0183] A ray tracing model of a plano-plano structure using a
lenticular array has been created with the cusps pointing down,
away from the light source, and toward the higher index material.
The repeat period is 100 micro meters, the index of refraction of
the top layer is 1.34, and the index of refraction of the bottom
layer is 1.506. The distance from the cusp apex point to the
viewing plane is 26.5 micro meters. FIG. 15A is a 3-dimensional
rendering of this structure. FIG. 15B shows a portion of the cross
section of this structure and the intensity profile created by the
ray tracing program, TracePro6.0.RTM.. The intensity profile is
normalized by the intensity that would have been seen in the
absence of the plano-plano structure. A merit function has been
created as a measure of the integrated increase in intensity in the
bright areas. In this case the merit function is 8.3% from the ray
trace data. The parameter s is half the dark space length in the
intensity profile. This measures to be 3 micro meters in this
example.
Example 14
[0184] A ray tracing model of a plano-plano structure using an
array of prism structures has been created with the cusps pointing
down, away from the light source, and toward the higher index
material. The repeat period is 50 micro meters, the index of
refraction of the top layer is 1.34, and the index of refraction of
the bottom layer is 1.4. The cusp half angle is 45 degrees. The
distance from the cusp apex point to the viewing plane is 119 micro
meters. FIG. 16A is a 3-dimensional rendering of this structure.
FIG. 16B shows a portion of the cross section of this structure and
the intensity profile created by the ray tracing program,
TracePro6.0.RTM.. The intensity profile is normalized by the
intensity that would have been seen in the absence of the
plano-plano structure. A merit function has been created as a
measure of the integrated increase in intensity in the bright
areas. In this case the merit function is 24.9% from the ray trace
data compared to 25% from an optimistic design estimate. The
parameter s is half the dark space length in the intensity profile.
The value of s measured from the ray tracing intensity profile is 5
micro meters in this example, which is exactly that which is
calculated from the design equations.
Example 15
[0185] A physical example of a plano-plano structure using an array
of prism structures has been created with the cusps pointing down,
away from the light source, and toward the higher index material. A
two-part silicone rubber (RTV-615 from Momentive Performance
Materials Inc, Waterford, N.Y.) was prepared as follows: one part
(0.25 g) of RTV-615-B and ten parts (2.5 g) of RTV-615-A were
placed in a glass vial and mixed manually with a spatula until the
mixture appeared homogenous. A small amount of this mixture was
placed on the prismatic surface of a 2''.times.2'' piece of
Reflexite.RTM. Coliimating Film (RCF-90L-PT from Reflexite Display
Optics, Rochester, N.Y.) and spread to completely cover the
surface. The sample was placed in a vacuum oven at .about.150 mm Hg
at room temperature for about two hours until all the trapped air
bubbles disappeared from the silicone layer. The sample was then
placed in an oven at 100.degree. C. for one hour to completely cure
the silicone polymer. The bilayer film obtained was 520 micron
thick.
[0186] A 3D rendering of a portion of the Reflexite.RTM. film is
shown in FIG. 17A. The period of the saw tooth pattern at the top
surface is about 48 microns, the depth of the saw-tooth pattern is
about 24 microns, and the cusp angle with respect to the normal to
the film plane is 45 degrees. A 3D rendering of a portion of the
Reflexite.RTM. film covered with the silicone polymer layer is
shown in FIG. 17B. In FIG. 17B the normal incident, plane parallel
light enters the sample from the top, i.e., the side coated with
the silicone polymer which has an index of refraction of about
1.40. The index of refraction of the Reflexite.RTM. film is higher
than that of the silicone polymer. A microscope with a camera was
used to capture the intensity profile created by the plano-plano
structure. Referencing FIG. 17B, the microscope is looking up from
the bottom of the sample into the light. The focal plane of the
microscope was placed about 132 micro meters below the apex of the
cusps pointing downward. FIG. 17C shows the micrograph of this
intensity profile. The size of this image is about 172 by 230 micro
meters. Exactly below the micrograph in FIG. 17C is a normalized
intensity profile across the horizontal of this image. The
intensity has been normalized to a white image taken at the same
illumination but without the sample. A correction to the normalized
intensity was introduced to compensate for top and bottom the
surface reflections of the plano-plano structure. If we arbitrarily
define the dark space created by this structure to be where the
intensity drops below 0.6 of the illumination intensity, then the
dark space measures from the intensity profile to be 17.8 micro
meters. An optimistic estimate of the merit function of this design
is 58.9%. This is calculated as 100*((period/bright distance)-1),
where the period is 48 micro meters, and the bright distance in
this case is (48-17.8) or 30.2 micro meters. A calculation of the
merit function achieved from the intensity profile shown in FIG.
17C is 33.9%.
Example 16
[0187] A ray tracing model of a plano-plano structure using a
lenticular array has been created with the cusps pointing up,
toward the light source, and toward the lower index material. The
repeat period is 100 micro meters, the index of refraction of the
top layer is 1.34, and the index of refraction of the bottom layer
is 1.506. The distance from the cusp apex point to the viewing
plane is 50 micro meters. The 3 dimensional rendering of this
object is the same as for Example 12 as shown in FIG. 14A. The
difference between the examples is that the index of refraction top
to bottom has been reversed. FIG. 18 shows a portion of the cross
section of this structure and the intensity profile created by the
ray tracing program, TracePro6.0.RTM.. The intensity profile is
normalized by the intensity that would have been seen in the
absence of the plano-plano structure. The parameter s is half the
bright space length in the intensity profile. This measures to be
3.5 micro meters in this example. This is of course not the optimal
way of using this lens structure to concentrate light. For a lens
structure
* * * * *