U.S. patent application number 12/981899 was filed with the patent office on 2012-11-22 for high throughput parallel backside contacting and periodic texturing for high-efficiency solar cells.
This patent application is currently assigned to UT-Battelle, LLC. Invention is credited to Craig Blue, Claus Daniel, Ronald Ott.
Application Number | 20120291854 12/981899 |
Document ID | / |
Family ID | 46379656 |
Filed Date | 2012-11-22 |
United States Patent
Application |
20120291854 |
Kind Code |
A2 |
Daniel; Claus ; et
al. |
November 22, 2012 |
HIGH THROUGHPUT PARALLEL BACKSIDE CONTACTING AND PERIODIC TEXTURING
FOR HIGH-EFFICIENCY SOLAR CELLS
Abstract
Disclosed are configurations of long-range ordered features of
solar cell materials, and methods for forming same. Some features
include electrical access openings through a backing layer to a
photovoltaic material in the solar cell. Some features include
textured features disposed adjacent a surface of a solar cell
material. Typically the long-range ordered features are formed by
ablating the solar cell material with a laser interference pattern
from at least two laser beams.
Inventors: |
Daniel; Claus; (Knoxville,
TN) ; Blue; Craig; (Knoxville, TN) ; Ott;
Ronald; (Knoxville, TN) |
Assignee: |
UT-Battelle, LLC
Oak Ridge
TN
37831
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20120167956 A1 |
July 5, 2012 |
|
|
Family ID: |
46379656 |
Appl. No.: |
12/981899 |
Filed: |
December 30, 2010 |
Current U.S.
Class: |
136/251;
257/E31.124; 257/E31.13; 438/71; 438/98 |
Current CPC
Class: |
H01L 31/02363 20130101;
Y02E 10/50 20130101 |
Class at
Publication: |
136/251; 438/098;
438/071; 257/E31.124; 257/E31.13 |
International
Class: |
H01L 31/05 20060101
H01L031/05; H01L 31/18 20060101 H01L031/18 |
Goverment Interests
GOVERNMENT RIGHTS
[0001] This invention was made with government support under
Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of
Energy. The government has certain rights in the invention.
Claims
1. A method of fabricating a pattern of long-range ordered
electrical access openings to a photovoltaic material in a solar
cell having a backing layer comprising ablating the backing layer
with a laser interference pattern from at least two laser beams to
form the pattern of electrical access openings through the backing
layer to the photovoltaic material.
2. The method of claim 1 wherein ablating the backing layer with
the laser interference pattern from the at least two laser beams
forms the pattern of electrical access openings as line-like
openings through the backing layer to the photovoltaic
material.
3. The method of claim 1 comprising ablating the backing layer with
at least three laser beams to form the pattern of electrical access
openings as dot-like openings through the backing layer to the
photovoltaic material.
4. The method of claim 1 wherein the laser interference pattern is
defined at least in part by a modal pattern with an intensity
variation wavelength having an average spacing distance between
lines that is within a range from approximately 1 micrometer to
approximately 50 micrometers.
5. A solar cell having a pattern of long-range ordered electrical
access openings through a backing layer to a photovoltaic material
wherein: the backing layer has a thickness that is within a range
from approximately 0.5 micrometers to approximately 10 micrometers;
the pattern of long-range ordered electrical access openings has a
plurality of spacing distances between the access openings with an
average spacing distance between the openings that is within a
range from approximately 1 micrometer to approximately 50
micrometers; and the long-range ordered electrical access openings
have an average width that is within a range from approximately 0.5
micrometers to approximately 10 micrometers.
6. The solar cell of claim 5 wherein the plurality of spacing
distances between the electrical access openings have a standard
deviation that is within a range from about ten percent to about
fifty percent of the average spacing distance between the
openings.
7. A method of fabricating a pattern of long-range ordered textured
features on a surface of a solar cell material comprising ablating
the surface of the solar cell material with a laser interference
pattern from at least two laser beams to form the pattern of
textured features.
8. The method of claim 7 comprising ablating the surface of the
solar cell material with the laser interference pattern from the at
least two laser beams to form the pattern of textured features as
line-like features.
9. The method of claim 7 comprising ablating the surface of the
solar cell material with at least three laser beams to form the
pattern of textured features as dot-like textured features.
10. The method of claim 7 comprising ablating the surface of the
solar cell material with at least three laser beams to form the
pattern of textured features as net-like textured features.
11. The method of claim 7 wherein the laser interference pattern is
defined at least in part by a modal pattern with an intensity
variation wavelength having an average spacing distance between
lines that is within a range from approximately 1 micrometer to
approximately 50 micrometers.
12. A solar cell having a pattern of long-range ordered textured
features disposed adjacent a surface of a solar cell material
wherein: the pattern of textured features has an average spacing
distance between the features that is within a range from
approximately 1 micrometer to approximately 50 micrometers; and the
textured features have an average width that is within a range from
approximately 0.5 micrometers to approximately 10 micrometers.
Description
FIELD
[0002] This disclosure relates to the field of solar cells. More
particularly, this disclosure relates to pattern features for solar
cells to enhance photon absorption and electrical conductivity.
BACKGROUND
[0003] Solar cells are typically fabricated as layers of materials.
For example a typical silicon solar cell has a top encapsulating
layer made of glass or other clear material such clear plastic to
seal the cell from the external environment, a silicon layer having
n-type silicon and p-type silicon sub-layers with a pn-junction
between them, an optional antireflective layer between the
encapsulating layer and the silicon layer, a top grid disposed
adjacent the top of the silicon layer (the cathode), and a metal
backing layer under the silicon layer (the anode).
[0004] Improved photovoltaic efficiency is a continuing goal for
wafer-silicon-based photovoltaic cells. Reducing cell thickness is
one way to obtain increased efficiency and meet other desirable
design criteria, such as reduced weight. Typically, aluminum is
used as a full area back reflector and electrical connector for
solar cells. However, reducing the thickness of the aluminum
reflector may result in significant warping of the cell. Improving
photo absorption is another way to improve photovoltaic efficiency.
However, many solar cell materials have high reflectance
properties, which reduce the amount of photo energy absorbed by the
solar cell. What are needed therefore are improved backing
structures for solar cells that provide adequate electrical
conductivity and physical strength with a reduction in weight, and
improved configurations of solar cell materials that reduce
reflectance and enhance absorption of solar energy.
SUMMARY
[0005] The present disclosure provides methods of fabricating a
pattern of long-range ordered electrical access openings to a
photovoltaic material in a solar cell having a backing layer. The
methods typically involves ablating the backing layer with a laser
interference pattern from at least two laser beams to form the
pattern of electrical access openings through the backing layer to
the photovoltaic material. Also disclosed are solar cells having a
pattern of long-range ordered electrical access openings through a
backing layer to a photovoltaic material. Generally the backing
layer has a thickness that is within a range from approximately 0.5
micrometers to approximately 10 micrometers. Typically the pattern
of electrical access openings has an average spacing distance
between the openings that is within a range from approximately 1
micrometer to approximately 50 micrometers and the electrical
access openings have an average width that is within a range from
approximately 0.5 micrometers to approximately 10 micrometers.
Further disclosed are methods of fabricating a pattern of
long-range ordered textured features on a surface of a solar cell
material. The methods typically involve ablating the surface of the
solar cell material with a laser interference pattern from at least
two laser beams to form the pattern of textured features. The
disclosure also provides a solar cell having a pattern of
long-range ordered textured features disposed adjacent a surface of
a solar cell material. Generally the pattern of textured features
has a plurality of spacing distances between the features with an
average spacing distance that is within a range from approximately
1 micrometer to approximately 50 micrometers, and the textured
features have an average width that is within a range from
approximately 0.5 micrometers to approximately 10 micrometers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Various advantages are apparent by reference to the detailed
description in conjunction with the figures, wherein elements are
not to scale so as to more clearly show the details, wherein like
reference numbers indicate like elements throughout the several
views, and wherein:
[0007] FIG. 1 is a somewhat schematic view of a laser
interferometry system for modification of a solar cell
material.
[0008] FIGS. 2A and 2B are somewhat schematic cross-sectional views
of repetitive patterns applied to solar cell materials.
[0009] FIGS. 3A, 3B, and 3C are schematic illustrations of
repetitive patterns of micro-features for solar cell materials.
[0010] FIGS. 4A and 4B are somewhat schematic illustrations of
electrical access openings in a backing layer of a solar cell
assembly.
[0011] FIG. 5 is a somewhat schematic illustration of textured
features of a solar cell material.
DETAILED DESCRIPTION
[0012] In the following detailed description of the preferred and
other embodiments, reference is made to the accompanying drawings,
which form a part hereof, and within which are shown by way of
illustration the practice of specific embodiments of solar cells
having a pattern of electrical access openings through a backing
layer to a photovoltaic material, and solar cells having a pattern
of textured features in the surface of a solar cell material. Solar
cell materials include any layer of a solar cell structure,
including encapsulating layers, photovoltaic material layers (e.g.,
silicon layers), antireflective layers, grid layers, and backing
layers. The following detailed description further presents
preferred and other embodiments of methods of fabricating a pattern
of electrical access openings to a photovoltaic material in a solar
cell having a backing layer and methods of fabricating a pattern of
textured features on a surface of a solar cell material. It is to
be understood that other embodiments may be utilized, and that
structural changes may be made and processes may vary in other
embodiments.
[0013] As previously indicated, replacement of the conventional
aluminum backing layer used in wafer-silicon-based photovoltaic
cells with a lighter and preferably more electrically and
photo-optically efficient material is one approach to improving the
attractiveness of photovoltaic solar cells. Cold-sprayed or
stress-adapted dielectric or electrically insulative thin films are
potential candidates for replacing the aluminum backing layer. An
example of such a thin film is layered SiO.sub.2/SiN/SiO.sub.2.
While such materials may have some desirable properties they
typically do not provide an efficient anode. Disclosed herein are
configurations of solar cells having direct electrical access to
the bottom side (typically the p-type sub-layer) of the silicon
layer of a solar cell through a plurality of electrical access
openings formed in the backing layer. Such openings are typically
formed by methods disclosed herein for ablating the backing layer
with a laser interference pattern from at least two laser beams to
form the pattern of electrical access openings that pass entirely
through the backing layer to the photovoltaic material.
[0014] Further disclosed herein are configurations of solar cells
having a textured pattern on a surface of a solar cell material.
Such textured patterns may be used, for example, to reduce the
reflectivity of a surface or to improve adhesion of bonding
materials. Such textured features are typically formed by methods
disclosed herein for ablating the surface of a solar cell material
with a laser interference pattern from at least two laser beams to
form the pattern of textured features.
[0015] During such laser interference structuring, a primary laser
beam is typically divided into two or more coherent beams that are
then guided by an optical system to interfere with each other at
the sample surface. The standing optical wave describes a periodic
intensity pattern having an intensity variation wavelength. The
pattern may be a one-dimensional line-like pattern or a
two-dimensional net-like or dot-like pattern, or a combination of a
one-dimensional and two-dimensional pattern. As used herein the
suffix "-like" is used to indicate that the indicated features have
the same or nearly the same appearance that is indicated by the
noun it follows. So for example, a "dot-like" feature has the
appearance of a dot, or nearly the same appearance as a dot.
[0016] The angles between the beams define the two-dimensional
interference fringe spacing in the intensity distribution. Spacing
may be calculated for a two-beam interference experiment by
employing the following formula: d = .lamda. 2 .times. .times. sin
.times. .times. .phi. Eq ' .times. n .times. .times. 1 ##EQU1##
where .phi. is the angle between the two incident beams and .lamda.
is the wavelength of the light. While Equation 1 indicates that the
spacing of the intensity distribution may be scaled down to half of
the laser wavelength, the practical limit is typically from
approximately 50 to 100 .mu.m due to various equipment limitations.
Two or more planar laser beams guided by an optical system may be
used to create various interference patterns. For example, two
beams may be employed to create line-like openings in a solar cell
backing layer. Three or more non-planar beams may be used to create
net-like or dot-like openings in a solar cell backing layer.
[0017] FIG. 1 illustrates an exemplary laser interference system. A
first laser beam 40 and a second laser beam 42 are directed at
backing layer 44 of a solar cell 46, to form an interference
pattern that produces a plurality of open spaces 48 in the backing
layer 44. Typically both the first laser beam 40 and the second
laser beam 42 may be one or more pulses from a Nd:YAG laser, each
typically from one up to approximately ten nanoseconds in duration.
However in alternate embodiments other lasers may be used and
pulses may range from femtoseconds, to over picoseconds, to
nanoseconds, to milliseconds. The plurality of open spaces 48
extend over a structured area distance 50 (in one dimension) that
may range from a few hundred micrometers to approximately 10
millimeters. The structured area diameter 50 may increase as laser
power increases. With current-generation lasers the structured area
diameter 50 is typically 5-8 mm. Next generation of lasers may
provide sufficient power to increase the diameter to perhaps
several centimeters or more.
[0018] Generally half wavelength structuring cannot be achieved for
most materials. Even in the case where the intensity distribution
shows fringe spacing on the sub-micrometer scale, the lowest
spacing length is limited by the heat transfer in the material. In
metals, for example, the optical energy delivered is mainly
converted into heat, which then follows the three-dimensional heat
diffusion equation. The heat diffusion length depends on the
interaction time of the laser with the material.
[0019] The heat diffusion length is defined as the distance from
the heat source in which the temperature is lowered to the 1/e
fraction of the initial temperature. This length grows with longer
pulse duration and can be approximated with Equation 2. l diff
.apprxeq. 2 .times. ( .tau. p .times. .kappa. t .rho. .times.
.times. c p ) 1 / 2 Eq ' .times. n .times. .times. 2 ##EQU2## where
t.sub.p is the pulse duration or involved time regime; k.sub.t is
the thermal conductivity of irradiated material; r is the density;
and c.sub.p is the thermal capacity. The minimum feature size
cannot be smaller than the periodicity of the intensity pattern or
the diffusion length, whichever is greater.
[0020] In the case of ultra-short femto second (fs) laser pulses,
Equation 2 predicts a limit which is much lower than half of the
laser wavelength. Therefore, a feature spacing of half of the
wavelength may be possible. Even in this case, however, a feature
spacing equal to half of the laser wavelength may not be achieved
in practice. Based on a two-temperature model for fs-laser
irradiation, an interaction time of up to 100 ps may be predicted,
which is three orders of magnitude longer than the pulse itself. If
one counts that as "pulse duration," the diffusion length can be
approximated at 200 nm (for copper).
[0021] Another issue based on the use of an fs-laser should
generally be considered. According to the speed of light, a pulse
in air with duration of about 100 fs has a length of about 30
.mu.m. Therefore, the path length of each beam has to be precisely
adjusted. It may be possible to provide such precision by using an
optical delay line in one of the beam paths. The theoretical limit
for the distance in any intensity distribution pattern is given by
the diffraction limit which is about 1/2 times the wavelength used.
However, this is only possible for extremely short pulses (ps/fs).
For longer pulses the theoretical limit of resolution of this
pattern into a physical structure is limited by the thermal
diffusivity and the laser pulse duration, i.e., essentially how far
heat can travel when the laser is on. For 10 ns in copper, this is
limited to about 2 um. As a result, it may be possible to produce
only a topographic texturing of a solar cell material layer (and
not full penetration of some solar cell material layers) with an
fs-laser.
[0022] Micro-features that are formed adjacent the surfaces of
materials or through materials may exhibit short-range ordered
patterns or long-range ordered patterns or a combination of both
patterns. Short-range ordered patterns and long-range ordered
patterns are collectively referred to as repetitive patterns. FIG.
2A illustrates a plurality of short-range ordered patterns. In FIG.
2A a material 80 has a surface 82 that includes a plurality of
topographical variations, 84, 86, 88, 90, and 92. Short-range
ordered patterns are characterized by feature spacings that are
constant only for a few adjacent features. For example, features
88a, 88b, 88c and 90a are adjacent features. The spacing between a
first feature 88a and its nearest neighbor feature 88b is a pattern
spacing distance 94. The spacing between the first feature 88a and
(in one direction) its second-nearest neighbor feature 88c is a
separation distance 96 that is substantially two times the pattern
spacing distance 94. However the spacing between the first feature
88a and its third nearest neighbor feature 90a is a distance 98
that is not substantially three times the pattern spacing distance
94. Short-range ordered patterns may have feature spacings that are
constant for two nearest neighbors, or three nearest neighbors, or
four nearest neighbors, but not for more than about five nearest
neighbors.
[0023] FIG. 2B illustrates a long-range ordered pattern. A material
100 has a surface 102 that includes a plurality of topographical
variations, including features 104, 106, 108, and 110. The spacing
between a first feature 104 and (in one direction) its nearest
neighbor feature 106 is a pattern spacing distance 120. The spacing
between the first feature 104 and its second-nearest neighbor
feature 108 is a separation distance 122 that is substantially two
times the pattern spacing distance 120. The spacing between the
first feature 104 and its eighth-nearest neighbor feature 110 is a
separation distance 124 that is substantially eight times the
pattern spacing distance 120. Long-range ordered patterns may have
such constant spacing for 10, 100, 1000 or even more
repetitions.
[0024] As previously indicated, laser interference structuring
techniques may be used to create line-like structures and net-like
protuberances with two or more planar arranged beams and dot-like
structures with three or more non-planar beams. FIGS. 3A, 3B, and
3C illustrate some of the possibilities. FIG. 3A illustrates a
repetitive pattern of first line-like structures 170. The first
line-like structures 170 may be, for example, spaces that penetrate
entirely through a layer of material, or topographical peaks, or
locally densified regions, or other micro-features. FIG. 3A also
illustrates a repetitive pattern of second line-like structures
180. The second line-like structures 180 may be, for example,
spaces that penetrate entirely through a layer of material, or
topographical valleys, or locally untreated regions. FIG. 3B
illustrates a net-like structure 190. The net-like structure 190
includes a first repetitive pattern of line-like structures 200 and
a second repetitive pattern of line-like structures 210. The first
line-like structures 200 and the second line-like structures 210
may be, for example, spaces that penetrate entirely through a layer
of material, or topographical peaks, or locally densified regions,
or other micro-features. The first repetitive pattern of line-like
structures 200 is disposed at a non-zero angle (in this case
disposed at an orthogonal angle) to the second repetitive pattern
of line-like structures 210. In the embodiment of FIG. 3A the first
repetitive pattern of line-like structures 200 overlays the second
repetitive pattern of line-like structures 210. The first
repetitive pattern of line-like structures 200 and the second
repetitive pattern of line-like structures 210 are an example of
two overlaid and angulated repetitive patterns of micro-features.
The first repetitive pattern of line-like structures 170 and the
second repetitive pattern of line-like structures 180 in FIG. 3A
are overlaid repetitive patterns of micro-features. The first
repetitive pattern of line-like structures 170 and the second
repetitive pattern of line-like structures 180 in FIG. 3A are not
angulated repetitive patterns of micro-features because the first
repetitive pattern of line-like structures 170 and the second
repetitive pattern of line-like structures 180 are parallel to each
other (i.e., they are not disposed at a non-zero angle to each
other).
[0025] FIG. 3C illustrates dot-like structures 220. The dot like
structures 220 may be open spaces (holes) that penetrate entirely
through a layer of material or the dot-like structures 220 may be
topographical features disposed adjacent the surface of a material.
The dot-like structures 220 may be characterized as a first
repetitive pattern of dot-like structures 230 disposed at a
non-zero angle (in this case disposed at an orthogonal angle) to a
second repetitive pattern of dot-like structures 240, even though
each individual dot 250 is attributed to both the first repetitive
pattern of dot-like structures 230 and the second repetitive
pattern of dot-like structures 240. By virtue of this perspective
the first repetitive pattern of dot-like structures 230 and the
second repetitive pattern of dot-like structures 240 are an example
of angulated and overlaid repetitive patterns of
micro-features.
[0026] FIG. 4A illustrates a solar cell assembly 300 having an
encapsulating layer 304, a top grid 308, a photovoltaic material
layer 312 and a backing layer 316. The backing layer 316 typically
has a substantially constant thickness. Typically the thickness of
the backing layer 316 is within a range from approximately 0.5
micrometers to approximately 10 micrometers. Three laser beams have
been directed at the backing layer 316, indicated by modal patterns
328, 332, and 336. The modal patterns 328, 332, and 336 each have
an intensity variation wavelength that is defined by the spacing
distances between the lines representing each modal pattern. The
average spacing distance between the lines is typically within a
range from approximately 1 micrometer to approximately 50
micrometers. The modal patterns 328, 332, and 336 have created an
interference pattern at their points of intersection, which caused
a pattern of dot-like electrical access openings (holes) 340 to be
formed through the backing layer 316 to the photovoltaic material
layer 312. In other embodiments two laser beams may be used to form
a pattern of line-like electrical access openings. In other
embodiments more than three laser beams may be used to form a
pattern of electrical access openings. Typically electrical access
openings according to the present disclosure have openings with an
average width that is within a range from approximately 0.5
micrometers and 10 micrometers. FIG. 4B provides a magnified view
of a portion of the holes 340.
[0027] A benefit of the disclosed approach for electrical access
openings to a photovoltaic material in a solar cell is that
long-range ordered features may be provided, with such features
having near-perfect periodicity. Such uniformity is beneficial in
order to control the current density distribution in the
photovoltaic material. For example, referring again to FIG. 4B,
each of the interior holes 340 has six spacing distances in six
directions 352 between itself and its neighbors. Spacing distances
are measured from centerline to centerline. Typically the average
spacing distance between the openings is within a range from
approximately 1 micrometer to approximately 50 micrometers. It is
preferable that for at least a substantial portion of the interior
holes 340 that the standard deviation in spacing distances between
adjacent interior holes 340 in each of the six directions 352 be
within a range from about ten percent to about fifty percent of the
average spacing distance in that direction.
[0028] FIG. 5 illustrates the front surface of the solar cell
assembly 300 of FIGS. 4A and 4B. A plurality of long-range ordered
textured features 360 (in this case, lines) have been formed on a
surface (in this case, the front surface) of a solar cell material
(in this case the encapsulating layer 304). The textured features
360 were formed by ablating the surface of the encapsulating layer
304 with a laser interference pattern from two laser beams to form
the pattern of line-like textured features 360. In other
embodiments three laser beams may be used to form a pattern of
net-like textured features or a pattern of dot-like textured
features. In some embodiments more than three laser beams may be
used to form a pattern of textured features. The pattern of
textured features 360 has an average spacing distance between the
features that is within a range from approximately 1 micrometer to
approximately 50 micrometers. The textured features have an average
width that is within a range from approximately 0.5 micrometers to
approximately 10 micrometers.
[0029] Using readily available technology up to 79 million local
points may be created in one step on an area of approximately 0.27
cm.sup.2. With future laser systems of higher power and larger
beams, this capability is expected to increase dramatically.
Available high-power short-pulse systems are capable of treating a
surface of 1.35 cm.sup.2 in a single step with an area coverage
speed of up to 135 cm.sup.2/s. Thus a 400 cm.sup.2 wafer may be
processed in about 2.96 s.
[0030] Due to the periodic intensity distribution, controlled
high-temperature gradients of more than 1,000K over lateral
sub-micrometer distances may be realized without any significant
thermal damage or temperature rise in surrounding material. The
laser light is capable of controlling both the surface topography
and the surface microstructure. The laser pulse duration is
typically on the order of nanoseconds for sub-micrometer spacings
or femtoseconds for nano-sized spacings. Therefore, the technique
may, for example, result in a high-speed micro-metallurgical
treatment with grain sizes on the order of nanometers, feature
sizes of sub-micrometers to micrometers, and structured areas on
the order of a square centimeter in one step in a fraction of a
second. The shape and distribution of features introduced by the
interference pattern may be designed to follow precisely
calculations based on wave summation and are generally very
homogeneous. The patterns typically show a very high lateral
long-range order and obtain a specific chosen topographic frequency
for stress-reduced back side contact through a dielectric film. For
example, a process such as metal vapor deposition that is applied
over a perforated backing layer may be used to form micro- and
nano-sized aluminum contacts that are separated by distances of a
few micrometers. Such electrical contacts may collect a charge
without stressing the silicon and warping the cell.
[0031] Typically the technique does not require processing under
special (controlled) atmospheres, low or high pressure, or vacuum
systems. However, if other processes or the material composition
need special atmospheres or a vacuum, the technology may still be
used. For example, the laser beams may be freely guided through
windows to process solar cells in a vacuum system, or the entire
laser beam interference apparatus may be placed inside a controlled
atmosphere chamber. Thus, the options for noncontact "optical
stamping" with or without a special atmosphere provide a high
degree of flexibility.
[0032] Optimization through wavelength selection, pulse number,
energy delivery per laser pulse, and geometric arrangement of
optics enables precise control of feature sizes and etching
(ablation) depth. The additional effect of absorption coefficient
change and absorption mechanism participation in a
multiple-material system may be used to create customized threshold
photo-property definitions. For example, a combination of
photochemical and photothermal absorption may be utilized to
establish a specific temperature rise and etching depth. The
capability to make abrupt changes in these mechanisms may provide
very precise control of defined etching steps, such as stop-go
criteria control to etch or ablate a material until another
material reaches the surface.
[0033] In summary, embodiments disclosed herein provide a
noncontact mode of structuring of solar cell surfaces that is very
flexible compared with conventional contact mode processes such as
stamping or nano-imprinting. This laser processing technology with
little or no surface damage offers the potential for high-quality
contacts on the back as well as texturing the front surface,
resulting in high-performance, low-cost solar cells. The foregoing
descriptions of embodiments have been presented for purposes of
illustration and exposition. They are not intended to be exhaustive
or to limit the embodiments to the precise forms disclosed. Obvious
modifications or variations are possible in light of the above
teachings. The embodiments are chosen and described in an effort to
provide the best illustrations of principles and practical
applications, and to thereby enable one of ordinary skill in the
art to utilize the various embodiments as described and with
various modifications as are suited to the particular use
contemplated. All such modifications and variations are within the
scope of the appended claims when interpreted in accordance with
the breadth to which they are fairly, legally, and equitably
entitled.
* * * * *