U.S. patent application number 13/550086 was filed with the patent office on 2013-07-18 for diamond-like carbon electronic devices and methods of manufacture.
The applicant listed for this patent is Chien-Min Sung. Invention is credited to Chien-Min Sung.
Application Number | 20130180576 13/550086 |
Document ID | / |
Family ID | 39082763 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130180576 |
Kind Code |
A1 |
Sung; Chien-Min |
July 18, 2013 |
Diamond-Like Carbon Electronic Devices and Methods of
Manufacture
Abstract
Materials, devices, and methods for enhancing performance of
electronic devices such as solar cells, fuels cells, LEDs,
thermoelectric conversion devices, and other electronic devices are
disclosed and described. A diamond-like carbon electronic device
can include a conductive diamond-like carbon cathode having
specified carbon, hydrogen and sp.sup.2 bonded carbon contents. In
some cases, the sp.sup.2 bonded carbon content may be sufficient to
provide the conductive diamond-like carbon material with a visible
light transmissivity of greater than about 0.70. A charge carrier
separation layer can be coupled adjacent and between the
diamond-like carbon cathode and an anode. The conductive
diamond-like carbon material of the present invention can be useful
for any other application which can benefit from the use of
conductive and transparent electrodes which are also chemically
inert, radiation damage resistance, and are simple to
manufacture.
Inventors: |
Sung; Chien-Min; (Tansui,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sung; Chien-Min |
Tansui |
|
TW |
|
|
Family ID: |
39082763 |
Appl. No.: |
13/550086 |
Filed: |
July 16, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13111052 |
May 19, 2011 |
8227812 |
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13550086 |
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12826502 |
Jun 29, 2010 |
7951642 |
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13111052 |
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11893589 |
Aug 14, 2007 |
7745831 |
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12826502 |
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60837885 |
Aug 14, 2006 |
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Current U.S.
Class: |
136/255 ;
136/252; 257/77; 438/105 |
Current CPC
Class: |
H01L 31/022466 20130101;
H01L 31/1884 20130101; Y02E 10/547 20130101; H01L 31/028 20130101;
Y02E 10/50 20130101; H01L 31/0725 20130101 |
Class at
Publication: |
136/255 ;
136/252; 438/105; 257/77 |
International
Class: |
H01L 31/0725 20060101
H01L031/0725; H01L 31/028 20060101 H01L031/028 |
Claims
1. A diamond-like carbon electronic device, comprising: a) a
diamond-like carbon cathode including a conductive diamond-like
carbon material having an sp.sup.a bonded carbon content from about
30 atom % to about 90 atom %, a hydrogen content from 0 atom % to
about 30 atom %, and an sp.sup.2 bonded carbon content from about
10 atom % to about 70 atom %; b) a charge carrier separation layer
adjacent the diamond-like carbon cathode; and c) an anode adjacent
the charge carrier separation layer opposite the diamond-like
carbon cathode.
2. The device of claim 1, wherein the conductive diamond-like
carbon material further includes a dopant selected from the group
consisting of B, N, Si, P, Li, or combinations thereof
3. The device of claim 1, wherein the sp.sup.2 bonded carbon
content is sufficient to provide the conductive diamond-like carbon
material with a visible light transmissivity of greater than about
0.70.
4. The device of claim 1, wherein the sp.sup.2 bonded carbon
content is from about 35 atom % to about 60 atom %.
5. The device of claim 1, wherein the hydrogen content is from
about 15 atom % to about 25 atom %.
6. The device of claim 1, wherein at least one of the diamond-like
carbon cathode and anode further include a conductive additive
selected from the group consisting of conductive metal particles,
carbon nanotubes, graphite, conductive nanoparticles, and
combinations thereof
7. The device of claim 1, wherein the charge carrier separation
layer is a semiconductor layer.
8. The device of claim 1, wherein the charge carrier separation
layer comprises at least a portion of a p-n or p-i-n junction and
the diamond-like carbon electronic device is a solar cell.
9. The device of claim 8, wherein the semiconductor layer comprises
a member selected from the group consisting of silicon, gallium
arsenide, gallium indium phosphide, gallium indium nitride, copper
indium diselenide, cadmium telluride, and composites or
combinations thereof
10. The device of claim 9, wherein the semiconductor layer
comprises silicon.
11. The device of claim 8, wherein the charge carrier separation
layer further comprises multiple p-n or p-i-n junctions to form a
multi-junction solar cell.
12. The device of claim 10, wherein the charge carrier separation
layer further includes an n-doped region and a p-doped region.
13. The device of claim 10, wherein the charge carrier separation
layer includes a p-doped region and the diamond-like carbon cathode
includes an n-doped region.
14. The device of claim 8, wherein the charge carrier separation
layer is substantially planar.
15. The device of claim 8, wherein the diamond-like carbon cathode
is a single layer and is configured as a passivation layer and an
anti-reflection layer.
16. The device of claim 12, wherein the diamond-like carbon
electronic device is a fuel cell.
17. The device of claim 1, wherein the charge separation carrier
layer comprises a crystalline material.
18. The device of claim 1, wherein the charge carrier separation
layer is compositionally graded.
19. The device of claim 1, wherein the charge carrier separation
layer has a thickness from about 10 .mu.m to about 300 .mu.m.
20. A method of forming a diamond-like carbon electronic device,
comprising: a) preparing a charge carrier separation layer; b)
forming an anode, said anode being coupled adjacent the charge
carrier separation layer; c) forming a diamond-like carbon cathode
coupled to the charge carrier separation layer opposite the anode,
said diamond-like carbon cathode including a diamond-like carbon
material having a conductivity from about 0 .mu..OMEGA.-cm to about
80 .mu..OMEGA.-cm at 20.degree. C. and a visible light
transmissivity from about 0.5 to about 1.0, said conductivity and
visible light transmissivity being a function of sp.sup.2 and
sp.sup.a bonded carbon content, hydrogen content, and optional
conductive additives.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/111,052, filed on May 19, 2011, now issued
as U.S. Pat. No. 8,227,812, which is a continuation of U.S. patent
application Ser. No. 12/826,502, filed on Jun. 29, 2010, now issued
as U.S. Pat. No. 7,951,642, which is a divisional of U.S. patent
application Ser. No. 11/893,589, filed on Aug. 14, 2007, now issued
as U.S. Pat. No. 7,745,831, which claims the benefit of U.S.
Provisional Application No. 60/837,885, filed Aug. 14, 2006, each
of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to diamond-like
carbon materials, and to devices and methods that utilize
conductive diamond-like carbon material. Accordingly, the present
application involves the fields of physics, chemistry, electricity,
and material science.
BACKGROUND OF THE INVENTION
[0003] Solar cell technologies have progressed over the past
several decades resulting in significant contributions to potential
power sources in many different applications. Despite dramatic
improvements in materials and manufacturing methods, solar cells
still have efficiency limits well below theoretical efficiencies,
with current conventional solar cells having maximum efficiency of
around 26%. Various approaches have attempted to increase
efficiencies with some success. For example, prior approaches have
included light trapping structures and buried electrodes in order
to minimize surface area shaded by the conductive metal grid. Other
methods have included a rear contact configuration where
recombination of hole-electron pairs occurs along the rear side of
the cell.
[0004] However, these and other approaches still suffer from
drawbacks such as mediocre efficiencies, manufacturing
complexities, material costs, reliability, and radiation
degradation, among others. As such, materials capable of achieving
high current outputs by absorbing relatively low amounts of energy
from an energy source, and which are suitable for use in practical
applications continue to be sought through ongoing research and
development efforts.
SUMMARY OF THE INVENTION
[0005] Accordingly, the present invention provides materials,
devices, and methods for enhancing performance of electronic
devices such as solar cells, thermoelectric conversion devices and
other electronic devices. In accordance with the present invention,
a diamond-like carbon electronic device can include a diamond-like
carbon cathode. The cathode can comprise a conductive diamond-like
carbon material having an sp.sup.3 bonded carbon content from about
30 atom % to about 90 atom %, a hydrogen content from 0 atom % to
about 30 atom %, and an sp.sup.2 bonded carbon content from about
10 atom % to about 70 atom %. A charge carrier separation layer can
be coupled adjacent the diamond-like carbon cathode. Further, an
anode can be adjacent the charge carrier separation layer opposite
the diamond-like carbon cathode.
[0006] In another alternative aspect of the present invention, a
conductive diamond-like carbon material can comprise a diamond-like
carbon material having a resistivity from about 0 .mu..OMEGA.-cm to
about 80 .mu..OMEGA.-cm at 20.degree. C. such that the material is
electrically conductive. Further, the diamond-like carbon material
can have a visible light transmissivity from about 0.5 to about
1.0. The conductivity and visible light transmissivity can be a
function of sp.sup.2 and sp.sup.3 bonded carbon content, hydrogen
content, and optional conductive additives. For example, an
increase in sp.sup.2 bonded carbon content can increase
conductivity while decreasing transmissivity. Conversely, an
increase in hydrogen content and/or sp.sup.3 bonded carbon content
can lead to increases in transmissivity and decrease in
conductivity. Conductivity and transmissivity can also be affected
by introduction of additives such as dopants or conductive
materials.
[0007] The conductive diamond-like carbon material of the present
invention can be useful for a variety of applications such as, but
not limited to, solar cell electrodes, fuel cells, LED electrodes,
thermoelectric conversion devices, or any other application which
can benefit from the use of conductive and transparent electrodes
which are also chemically inert, radiation damage resistance, and
are simple to manufacture.
[0008] In one detailed aspect of the present invention, the charge
carrier separation layer can be a semiconductor layer to form a
solar cell. The diamond-like carbon cathode of the present
invention can allow for the semiconductor layer to be substantially
planar. For example, the solar cell can be free of trenches and/or
metal grid materials which are commonly present in conventional
silicon solar cells. Further, the charge carrier separation layer
can have a thickness from about 10 .mu.m to about 300 .mu.m.
[0009] In yet another detailed aspect of the present invention, the
charge carrier separation layer can form a multi-junction solar
cell. Alternatively, the charge carrier separation layer can
include a compositionally graded material including carbon and
semi-conductor.
[0010] The present invention further includes methods of forming a
diamond-like carbon electronic device. A charge carrier separation
layer can be prepared having desired properties and characteristics
designed for a particular device. An anode can be formed adjacent
the charge carrier separation layer. Further, a diamond-like carbon
cathode can be formed and coupled to the charge carrier separation
layer opposite the anode. Based on the following detailed
discussion, the diamond-like carbon cathode can include a
diamond-like carbon material having a conductivity from about 0
.mu..OMEGA.-cm to about 80 .mu..OMEGA.-cm at 20.degree. C. and a
visible light transmissivity from about 0.5 to about 1.0.
[0011] There has thus been outlined, rather broadly, the more
important features of the invention so that the detailed
description thereof that follows may be better understood, and so
that the present contribution to the art may be better appreciated.
Other features of the present invention will become clearer from
the following detailed description of the invention, taken with the
accompanying drawings and claims, or may be learned by the practice
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a side cross-sectional view of a conventional
silicon solar cell in accordance with the prior art.
[0013] FIG. 2 shows a side cross-sectional view of a diamond-like
carbon composite solar cell in accordance with one embodiment of
the present invention.
[0014] FIG. 3 shows a side cross-sectional view of a
compositionally graded diamond-like carbon composite solar cell in
accordance with another embodiment of the present invention.
[0015] FIG. 4 shows an SEM graph of amorphous diamond material
illustrating the variation in asperity size and shape.
[0016] FIG. 5 is a micrograph of a mosaic surface of a diamond-like
carbon material grown heteroepitaxially on a silicon substrate in
accordance with one aspect of the present invention.
[0017] The drawings will be described further in connection with
the following detailed description. Further, these drawings are not
necessarily to scale and are by way of illustration only such that
dimensions and geometries can vary from those illustrated.
DETAILED DESCRIPTION
[0018] Before the present invention is disclosed and described, it
is to be understood that this invention is not limited to the
particular structures, process steps, or materials disclosed
herein, but is extended to equivalents thereof as would be
recognized by those ordinarily skilled in the relevant arts. It
should also be understood that terminology employed herein is used
for the purpose of describing particular embodiments only and is
not intended to be limiting.
[0019] It must be noted that, as used in this specification and the
appended claims, the singular forms "a," "an," and "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "a layer" includes one or more of
such layers, reference to "an additive" includes reference to one
or more of such materials, and reference to "a cathodic arc
technique" includes reference to one or more of such
techniques.
[0020] Definitions
[0021] In describing and claiming the present invention, the
following terminology will be used in accordance with the
definitions set forth below.
[0022] As used herein, "charge carrier separation layer" refers to
any material or layer which provides an electric potential barrier
to free electron flow. Non-limiting examples of charge carrier
separation layers can include p-n junctions, p-i-n junctions,
electrolyte solutions, thin film junctions (e.g. thin dielectric
films), and the like.
[0023] As used herein, "electrode" refers to a conductor used to
make electrical contact between at least two points in a
circuit.
[0024] As used herein, "sp.sup.3 bonded carbon" refers to carbon
atoms bonded to neighboring carbon atoms in a crystal structure
substantially corresponding to the diamond isotope of carbon (i.e.
pure sp.sup.3 bonding), and further encompasses carbon atoms
arranged in a distorted tetrahedral coordination sp.sup.3 bonding,
such as amorphous diamond and diamond-like carbon.
[0025] As used herein, "sp.sup.2 bonded carbon" refers to carbon
atoms bonded to neighboring carbon atoms in a crystal structure
substantially corresponding to the graphitic isotope of carbon.
[0026] As used herein, "diamond" refers to a crystalline structure
of carbon atoms bonded to other carbon atoms in a lattice of
tetrahedral coordination known as sp.sup.3 bonding. Specifically,
each carbon atom is surrounded by and bonded to four other carbon
atoms, each located on the tip of a regular tetrahedron. Further,
the bond length between any two carbon atoms is 1.54 angstroms at
ambient temperature conditions, and the angle between any two bonds
is 109 degrees, 28 minutes, and 16 seconds although experimental
results may vary slightly. The structure and nature of diamond,
including many of its physical and electrical properties are well
known in the art.
[0027] As used herein, "distorted tetrahedral coordination" refers
to a tetrahedral bonding configuration of carbon atoms that is
irregular, or has deviated from the normal tetrahedron
configuration of diamond as described above. Such distortion
generally results in lengthening of some bonds and shortening of
others, as well as the variation of the bond angles between the
bonds. Additionally, the distortion of the tetrahedron alters the
characteristics and properties of the carbon to effectively lie
between the characteristics of carbon bonded in sp.sup.3
configuration (i.e. diamond) and carbon bonded in sp.sup.2
configuration (i.e. graphite). One example of material having
carbon atoms bonded in distorted tetrahedral bonding is amorphous
diamond. It will be understood that many possible distorted
tetrahedral configurations exist and a wide variety of distorted
configurations are generally present in amorphous diamond.
[0028] As used herein, "diamond-like carbon" refers to a
carbonaceous material having carbon atoms as the majority element,
with a substantial amount of such carbon atoms bonded in distorted
tetrahedral coordination. Diamond-like carbon (DLC) can typically
be formed by PVD processes, although CVD or other processes could
be used such as vapor deposition processes. Notably, a variety of
other elements can be included in the DLC material as either
impurities, or as dopants, including without limitation, hydrogen,
sulfur, phosphorous, boron, nitrogen, silicon, tungsten, etc.
[0029] As used herein, "amorphous diamond" refers to a type of
diamond-like carbon having carbon atoms as the majority element,
with a substantial amount of such carbon atoms bonded in distorted
tetrahedral coordination. In one aspect, the amount of carbon in
the amorphous diamond can be at least about 90%, with at least
about 20% of such carbon being bonded in distorted tetrahedral
coordination. Amorphous diamond also has a higher atomic density
than that of diamond (176 atoms/cm.sup.3). Further, amorphous
diamond and diamond materials contract upon melting.
[0030] As used herein, "transmissivity" refers to the portion of
light which travels across a material. Transmissivity is defined as
the ratio of the transmitted light intensity to the total incident
light intensity and can range from 0 to 1.0.
[0031] As used herein, "vapor deposited" refers to materials which
are formed using vapor deposition techniques. "Vapor deposition"
refers to a process of depositing materials on a substrate through
the vapor phase. Vapor deposition processes can include any process
such as, but not limited to, chemical vapor deposition (CVD) and
physical vapor deposition (PVD). A wide variety of variations of
each vapor deposition method can be performed by those skilled in
the art. Examples of vapor deposition methods include hot filament
CVD, rf-CVD, laser CVD (LCVD), laser ablation, conformal diamond
coating processes, metal-organic CVD (MOCVD), sputtering, thermal
evaporation PVD, ionized metal PVD (IMPVD), electron beam PVD
(EBPVD), reactive PVD, atomic layer deposition (ALD), and the
like.
[0032] As used herein, "asperity" refers to the roughness of a
surface as assessed by various characteristics of the surface
anatomy. Various measurements may be used as an indicator of
surface asperity, such as the height of peaks or projections
thereon, and the depth of valleys or concavities depressing
therein. Further, measures of asperity include the number of peaks
or valleys within a given area of the surface (i.e. peak or valley
density), and the distance between such peaks or valleys.
[0033] As used herein, "metallic" refers to a metal, or an alloy of
two or more metals. A wide variety of metallic materials are known
to those skilled in the art, such as aluminum, copper, chromium,
iron, steel, stainless steel, titanium, tungsten, zinc, zirconium,
molybdenum, etc., including alloys and compounds thereof
[0034] As used herein, "dielectric" refers to any material which is
electrically resistive. Dielectric materials can include any number
of types of materials such as, but not limited to, glass, polymers,
ceramics, graphites, alkaline and alkali earth metal salts, and
combinations or composites thereof
[0035] As used herein, "vacuum" refers to a pressure condition of
less than 10.sup.-2 torr.
[0036] As used herein, "electrically coupled" refers to a
relationship between structures that allows electrical current to
flow at least partially between them. This definition is intended
to include aspects where the structures are in physical contact and
those aspects where the structures are not in physical contact.
Typically, two materials which are electrically coupled can have an
electrical potential or actual current between the two materials.
For example, two plates physically connected together by a resistor
are in physical contact, and thus allow electrical current to flow
between them. Conversely, two plates separated by a dielectric
material are not in physical contact, but, when connected to an
alternating current source, allow electrical current to flow
between them by capacitive means. Moreover, depending on the
insulative nature of the dielectric material, electrons may be
allowed to bore through, or jump across the dielectric material
when enough energy is applied.
[0037] As used herein, "adjacent" refers to near or close
sufficient to achieve a desired affect. Although direct physical
contact is most common and preferred in the layers of the present
invention, adjacent can broadly allow for spaced apart
features.
[0038] As used herein, "thermoelectric conversion" relates to the
conversion of thermal energy to electrical energy or of electrical
energy to thermal energy, or flow of thermal energy.
[0039] As used herein, the term "substantially" refers to the
complete or nearly complete extent or degree of an action,
characteristic, property, state, structure, item, or result. The
exact allowable degree of deviation from absolute completeness may
in some cases depend on the specific context. However, generally
speaking the nearness of completion will be so as to have the same
overall result as if absolute and total completion were obtained.
The use of "substantially" is equally applicable when used in a
negative connotation to refer to the complete or near complete lack
of an action, characteristic, property, state, structure, item, or
result. For example, a composition that is "substantially free of"
particles would either completely lack particles, or so nearly
completely lack particles that the effect would be the same as if
it completely lacked particles. In other words, a composition that
is "substantially free of" an ingredient or element may still
actually contain such item as long as there is no measurable effect
on the property of interest thereof.
[0040] As used herein, the term "about" is used to provide
flexibility to a numerical range endpoint by providing that a given
value may be "a little above" or "a little below" the endpoint with
a degree of flexibility as would be generally recognized by those
skilled in the art. Further, the term about explicitly includes the
exact endpoint, unless specifically stated otherwise.
[0041] As used herein, a plurality of items, structural elements,
compositional elements, and/or materials may be presented in a
common list for convenience. However, these lists should be
construed as though each member of the list is individually
identified as a separate and unique member. Thus, no individual
member of such list should be construed as a de facto equivalent of
any other member of the same list solely based on their
presentation in a common group without indications to the
contrary.
[0042] Concentrations, amounts, and other numerical data may be
expressed or presented herein in a range format. It is to be
understood that such a range format is used merely for convenience
and brevity and thus should be interpreted flexibly to include not
only the numerical values explicitly recited as the limits of the
range, but also to include all the individual numerical values or
sub-ranges encompassed within that range as if each numerical value
and sub-range is explicitly recited. As an illustration, a
numerical range of "about 1 to about 5" should be interpreted to
include not only the explicitly recited values of about 1 to about
5, but also include individual values and sub-ranges within the
indicated range. Thus, included in this numerical range are
individual values such as 2, 3, and 4 and sub-ranges such as from
1-3, from 2-4, and from 3-5, etc., as well as 1, 2, 3, 4, and 5,
individually. This same principle applies to ranges reciting only
one numerical value as a minimum or a maximum Furthermore, such an
interpretation should apply regardless of the breadth of the range
or the characteristics being described.
[0043] The Invention
[0044] FIG. 1 illustrates a conventional crystalline silicon solar
cell 10 in accordance with the prior art. An anti-reflection layer
12 is used to prevent excessive reflection of light from the
surface of the underlying silicon layer 14. The anti-reflection
layer is most often silicon nitride, although other materials have
also been used, and is electrically insulating. The silicon solar
cell shown in FIG. 1 is commonly referred to as a p-i-n solar cell
due to the respective n and p doping of cathode area 16 and anode
area 18 on either side of an insulating inner layer 20. A
conductive metal grid 22 is buried into the silicon layer. The
metal grid is typically formed of silver which is sintered at about
800.degree. C. or other conductive metals like copper or nickel.
The metal grid is embedded a significant distance into the
insulating layer, e.g. typically over about 400 to 500 nm. A
conductive metal such as silver or other suitable material is also
used as the anode 24. Although many other considerations are
important in designing solar cells, such are well within the
knowledge of one skilled in the art. Further, the above description
provides a suitable background for the following discussion of
various aspects of the present invention and the contribution
thereof to the art.
[0045] In one aspect of the present invention, a diamond-like
carbon electronic device may include a conductive diamond-like
carbon cathode, a charge carrier separation layer adjacent the
diamond-like carbon cathode, and an anode adjacent the charge
carrier separation layer opposite the diamond-like carbon cathode.
Another aspect of the present invention can include a diamond-like
carbon material having a resistivity from about 0 .mu..OMEGA.-cm to
about 80 .mu..OMEGA.-cm at 20.degree. C. such that the material is
electrically conductive. In another aspect the resistivity of the
conductive diamond-like carbon material can be from about 0
.mu..OMEGA.-cm to about 40 .mu..OMEGA.-cm. Further, the
diamond-like carbon material can have a visible light
transmissivity from about 0.5 to about 1.0. The conductivity and
visible light transmissivity can be a function of sp.sup.2 and
sp.sup.3 bonded carbon content, hydrogen content, and optional
conductive additives. For example, an increase in sp.sup.2 bonded
carbon content can increase conductivity while decreasing
transmissivity. Conversely, an increase in hydrogen content and/or
sp.sup.3 bonded carbon content can lead to increases in
transmissivity and decrease in conductivity. Conductivity and
transmissivity can also be affected by introduction of additives
such as dopants or conductive materials.
[0046] The conductive diamond-like carbon material of the present
invention can be useful for a variety of applications such as, but
not limited to, solar cell electrodes, LED electrodes, or other
applications where conductive and transparent electrodes which are
also chemically inert, radiation damage resistant, and are simple
to manufacture.
[0047] In accordance with one embodiment of the present invention,
a diamond-like carbon electronic device can include a diamond-like
carbon cathode. The cathode can comprise a conductive diamond-like
carbon material having an sp.sup.a bonded carbon content from about
30 atom % to about 90 atom %, a hydrogen content from 0 atom % to
about 30 atom %, and an sp.sup.2 bonded carbon content from about
10 atom % to about 70 atom %. A charge carrier separation layer can
be coupled adjacent the diamond-like carbon cathode. Further, an
anode can be adjacent the charge carrier separation layer opposite
the diamond-like carbon cathode. It should be noted that the terms
"cathode" and "anode" are intended to be interchangeable, and are
used to merely signify a difference in polarity between two
electrodes. For example, applications using alternating current
would involve electrodes which serve as both anode and cathode.
[0048] Referring now to FIG. 2, the diamond-like carbon electronic
device can be a solar cell 26. In this embodiment of the present
invention, the charge carrier separation layer can be a
semiconductor layer 28 adjacent an anode 36. The semiconductor
layer can be formed of any suitable material such as, but not
limited to, crystalline silicon, amorphous silicon, gallium
arsenide, gallium indium phosphide, gallium indium nitride, copper
indium diselenide, cadmium telluride, and composites or
combinations thereof In one embodiment of the present invention,
the charge carrier separation layer can comprise crystalline
silicon. In some cases, the charge carrier separation layer can
consist essentially of crystalline silicon, with the exception of
suitable dopants. In another preferred embodiment, the charge
carrier separation layer can comprise or consist essentially of
amorphous silicon, again with the exception of suitable dopants.
Crystalline-based charge carrier separation layers can be
particularly used in formation of solar cells. In contrast, a
partially or fully amorphous charge separation carrier layer can be
particularly useful in thermoelectric conversion devices, e.g.
those which convert heat into electricity.
[0049] Suitable charge separation carrier layers can be formed
using a variety of methods such as, but not limited to, vapor
deposition, epitaxial growth or the like. Most often, a starting
material such as a conventional silicon wafer can be used from
conventional commercial sources. The wafer can be cut from a solid
silicon ingot or boule. The wafer can be polished to have a smooth
surface. Alternatively, the semiconductor material can be formed
directly on a desired substrate or anode using vapor deposition or
other suitable techniques. Further, the wafer or semiconductor
surface can be etched to roughen the surface and/or may include
features such as pyramidal depressions or extensions which increase
functional surface areas of the device. These features can be
varied in size and geometry based on balancing performance, cost,
and material limitations. For example, etching of pyramidal
extensions or depressions can be particularly useful in enhancing
performance. Such extension and depressions are most often from
about 0.01 mm to about 0.7 mm, although other dimensions can be
useful.
[0050] Generally, the present invention also provides methods for
forming diamond-like carbon electronic devices. Such a method may
include forming an anode on a suitable charge carrier separation
layer and coupling a conductive diamond-like carbon cathode to the
charge carrier separation layer opposite the anode. The conductive
diamond-like carbon cathode may be formed on the charge carrier
separation layer opposite the anode, or it may be formed separately
therefrom and subsequently coupled thereto as described in more
detail throughout. Additionally, in one aspect the anode may be a
conductive diamond-like carbon anode.
[0051] The diamond-like carbon electronic devices of the present
invention allow for a significant reduction in the thickness of the
charge carrier separation layer. At least one reason for this is
the elimination or reduction of any buried metal grid electrodes.
The diamond-like carbon cathode of the present invention can allow
for the semiconductor layer to be substantially planar. For
example, the devices of the present invention can be free of
trenches and/or metal grid materials which are present in
conventional silicon solar cells. As a general guideline, the
charge carrier separation layer of the present invention can have a
thickness from about 10 .mu.m to about 300 .mu.m, and preferably
from about 50 .mu.m to about 150 .mu.m, with about 100 .mu.m being
currently most preferred. The use of conductive diamond-like carbon
material can also prevent these thinner semiconductor layers from
warping.
[0052] The charge carrier separation layer can most often be
configured as a p-i-n or p-n junction. For example, FIG. 2
illustrates a p-i-n junction where the charge carrier separation
layer comprises a semiconductor layer which is doped on each side
with either p- or n-doping materials. An n-doped area 30 can be
formed by conventional doping of the semiconductor layer 28.
Suitable n-dopants can include, but are not limited to,
phosphorous, arsenic, bismuth, antimony, and combinations thereof
Similarly, a p-doped area 32 can be formed by doping of the
semiconductor layer with dopants such as, but not limited to,
boron, aluminum, gallium, indium, thallium, and combinations
thereof The degree of doping can be controlled by the conditions
during doping such as dopant concentration, temperature, and the
like. The charge carrier separation layer can alternatively be
formed of distinct layers in a p-n configuration. Specifically, an
n-doped semiconductor layer can be formed adjacent a p-doped
semiconductor layer to form the charge carrier separation layer.
The semiconductor materials can be selectively doped using methods
such as, but not limited to, ion implantation, drive-in diffusion,
field-effect doping, electrochemical doping, vapor deposition, or
the like. Further, such doping can be accomplished by co-deposition
with the semiconductor material. For example, a boron source gas
and silicon or other semiconductor source gas can be simultaneously
present in a vapor deposition chamber.
[0053] The diamond-like carbon electronic device of the present
invention can include a cathode 34 comprising a conductive
diamond-like carbon material. The conductive diamond-like carbon
material of the present invention represents a distinct class of
diamond-like carbon materials having the properties identified
herein such as low resistivity, high transmissivity, etc. As
mentioned earlier, these properties are at least partially related
to variables such as hydrogen content, sp.sup.2 and sp.sup.a bonded
carbon content, and optional additives or dopants. Most often, the
conductive diamond-like material can be formed on the semiconductor
layer by a suitable vapor deposition process. Additionally, in one
specific embodiment, the diamond-like carbon material may be
amorphous diamond.
[0054] Increased hydrogen content can contribute to an increase in
transmissivity. The hydrogen content can be incorporated throughout
the conductive diamond-like material or substantially only at a
surface thereof In one embodiment, any hydrogen content can be
substantially only at external surfaces of the conductive
diamond-like material. As a general guideline, in one specific
embodiment the hydrogen content can range from 0 atom % to about 30
atom %. In another specific embodiment the hydrogen content can
range from about 15 atom % to about 25 atom %. In one alternative
embodiment, the conductive diamond-like carbon can be substantially
free of hydrogen content. However, hydrogen content can be
increased by increasing hydrogen gas concentrations during
deposition of the diamond-like carbon material. Alternatively, a
diamond-like carbon material can be heat treated with hydrogen gas
to form a hydrogen terminated surface layer of diamond-like carbon.
Typically, deposition occurs using a vapor deposition process such
as chemical vapor deposition, although other methods can be
suitable.
[0055] Increased hydrogen content can also be accompanied by
decreased conductivity, all other variables being factored out.
Therefore, it can sometimes be desirable to introduce a conductive
additive in relatively small amounts to increased conductivity.
Suitable conductive additives can be incorporated via any number of
approaches such as, but not limited to, codeposition in the vapor
phase, coating of the conductive additives by the diamond-like
carbon material, infiltration, alternating deposition of each
material, and the like. Suitable conductive additives can include
conductive metal particulates incorporated into a hydrogenated
diamond-like carbon material. Suitable metal particles can comprise
metals such as silver, copper, gold, titanium, or other similar
materials. In one specific aspect, the metal particles can be
nanoparticles, i.e. 100 nm or less and often 50 nm or less. Other
conductive additives can include, but are not limited to, carbon
nanotubes, graphite, and the like. In one particular scenario, the
conductive additive can be a graphite having a degree of
graphitization greater than 0.8 and often greater than 0.9.
Further, in order to avoid excessive decrease in transmissivity due
to the conductive additives the size and/or the concentration of
the additives can be decreased. Such particulates can be any
suitable size, although about 1 nm to about 1 .mu.m is typically
suitable with about 2 nm to about 100 nm being suitable and about
0.1 .mu.m to about 0.6 .mu.m being preferred. Smaller particle
sizes allow for increased transmissivity but also experience a
contrasting decrease in contribution to conductivity of the
diamond-like material. Similarly, concentration of metal additives
can generally range from about 2 vol % to about 60 vol %, although
optimal particle sizes and concentrations can vary considerably
depending on the specific particle material, sp.sup.2 and sp.sup.a
bonded carbon content, and hydrogen content. These same principles
can be equally applied to the anode side of the device.
[0056] Another important variable with respect to the conductive
diamond-like carbon material is the sp.sup.3 bonded carbon content.
Advantageously, an increase in sp.sup.3 bonded carbon content
results in an increase in transmissivity as the diamond character
of the material increase. However, this is also accompanied by an
associated decrease in conductivity. Generally, the conductive
diamond-like carbon material, whether at the cathode and/or anode
can have an sp.sup.3 bonded carbon content from about 30 atom % to
about 90 atom %. At higher sp.sup.3 bonded carbon contents, e.g.
from about 50 atom % to about 90 atom %, additional additives
and/or dopants can be introduced to increase conductivity
sufficient for use of the material as a conductive electrode within
the device. For example, doping with nitrogen or other similar
dopants can provide good results without significantly decreasing
transmissivity in the case of use in the cathode.
[0057] Further, sp.sup.2 bonded carbon content can also contribute
to decreased transmissivity. However, sp.sup.2 bonded carbon is
graphitic in crystal structure and is electrically conductive.
Therefore, an appropriate balance of sp.sup.2 bonded carbon content
should be considered. As a general guideline, in one embodiment the
conductive diamond-like carbon material can have from about 10 atom
% to about 70 atom % sp.sup.2 bonded carbon content. In another
embodiment, the conductive diamond-like carbon material can have
from about 35 atom % to about 60 atom %. However, the specific
content can depend on the hydrogen content, sp.sup.3 bonded carbon
content, and other optional additives and/or dopants. However, the
sp.sup.2 bonded carbon content can preferably be sufficient to
provide the conductive diamond-like carbon material with a visible
light transmissivity of greater than about 0.70, and most
preferably greater than about 0.90.
[0058] The diamond-like carbon material can be made using any
suitable method, such as various vapor deposition processes. In one
aspect of the invention, the diamond-like carbon material can be
formed using a cathodic arc method. Various cathodic arc processes
are well known to those of ordinary skill in the art, such as those
disclosed in U.S. Pat. Nos. 4,448,799; 4,511,593; 4,556,471;
4,620,913; 4,622,452; 5,294,322; 5,458,754; and 6,139,964, each of
which is incorporated herein by reference. Generally speaking,
cathodic arc techniques involve the physical vapor deposition (PVD)
of carbon atoms onto a target, or substrate. The arc is generated
by passing a large current through a graphite electrode that serves
as an anode, and vaporizing carbon atoms with the current. If the
carbon atoms contain a sufficient amount of energy (i.e. about 100
eV) they will impinge on the target and adhere to its surface to
form a carbonaceous material, such as amorphous diamond. Amorphous
diamond can be coated on almost any metallic substrate, typically
with no, or substantially reduced, contact resistance. In general,
the kinetic energy of the impinging carbon atoms can be adjusted by
the varying the negative bias at the substrate and the deposition
rate can be controlled by the arc current. Control of these
parameters as well as others can also adjust the degree of
distortion of the carbon atom tetrahedral coordination and the
geometry, or configuration of the amorphous diamond material (i.e.
for example, a high negative bias can accelerate carbon atoms and
increase sp.sup.a bonding). By measuring the Raman spectra of the
material the sp.sup.a/sp.sup.2 ratio can be determined However, it
should be kept in mind that the distorted tetrahedral portions of
the amorphous diamond layer are generally neither pure sp.sup.a nor
sp.sup.2 but a range of bonds which are of intermediate character.
Further, increasing the arc current can increase the rate of target
bombardment with high flux carbon ions. As a result, temperature
can rise so that the deposited carbon will convert to more stable
graphite. Thus, final configuration and composition (i.e. band
gaps, NEA, and emission surface asperity) of the diamond-like
carbon material can be controlled by manipulating the cathodic arc
conditions under which the material is formed.
[0059] Additionally, other processes can be used to form
diamond-like carbon such as various vapor deposition processes,
e.g. chemical vapor deposition or the like. In preparing more
crystalline diamond-like carbon, chemical vapor deposition can be
used. Chemical vapor deposition (CVD) of diamond-like carbon can
generally be performed by introducing a carbon source gas at
elevated temperatures into a chamber housing a deposition
substrate, e.g. semiconductor or charge separation carrier layer.
Diamond-like carbon is typically deposited using physical vapor
deposition (PVD) which involves impinging carbon atoms against a
substrate at relatively low deposition and plasma temperatures
(e.g. 100.degree. C.). Due to the low temperature of such PVD
methods, carbon atoms are not located at thermal equilibrium
positions. As a result, the film can be less stable with high
internal stress. Alternatively, CVD processes can be employed to
deposit diamond-like carbon. If the deposition temperature is high
(e.g. 800.degree. C.), diamond will grow to become a crystalline
CVD diamond film An example of a suitable CVD process is radio
frequency (13.6 MHz) CVD by dissociation of acetylene
(C.sub.2H.sub.2) and hydrogen gas under partial vacuum (millitorr).
Alternatively, pulsed DC can be used in stead of RF CVD. In the
case of amorphous diamond, deposition by cathodic arc or laser
ablation can form a suitable layer. Conductive diamond-like carbon
material can be used as the cathode and optionally also as the
anode of devices of the present invention.
[0060] The formation of the cathode and/or anode may be further
facilitated through the deposition of a conformal diamond-like
carbon layer. Conformal diamond coating processes can provide a
number of advantages over conventional diamond film processes.
Conformal diamond coating can be performed on a wide variety of
substrates, including non-planar substrates. A growth surface can
be pretreated under diamond growth conditions in the absence of a
bias to form a carbon film The diamond growth conditions can be
conditions which are conventional vapor deposition conditions for
diamond without an applied bias. As a result, a thin carbon film
can be formed which is typically less than about 100 angstroms. The
pretreatment step can be performed at almost any growth temperature
such as from about 200.degree. C. to about 900.degree. C., although
lower temperatures below about 500.degree. C. may be preferred.
Without being bound to any particular theory, the thin carbon film
appears to form within a short time, e.g., less than one hour, and
is a hydrogen terminated amorphous carbon.
[0061] Following formation of the thin carbon film, the growth
surface may then be subjected to diamond growth conditions to form
the diamond-like carbon layer. The diamond growth conditions may be
those conditions which are commonly used in traditional vapor
deposition diamond growth. However, unlike conventional amorphous
diamond film growth, an amorphous diamond film produced using the
above pretreatment steps results in a conformal amorphous diamond
film that typically begins growth substantially over the entire
growth surface with substantially no incubation time.
[0062] One aspect of the diamond-like carbon material that
facilitates electron emission is the distorted tetrahedral
coordination with which many of the carbon atoms are bonded.
Tetrahedral coordination allows carbon atoms to retain the sp.sup.a
bonding characteristic that provides a plurality of effective band
gaps, due to the differing bond lengths of the carbon atom bonds in
the distorted tetrahedral configuration.
[0063] In one aspect of the present invention, the upper exposed
surface of the electronic device can be configured to improve
energy absorption. Specifically, as shown in FIG. 2, the surface
area of the outer layer can be increased by forming features which
extend outwardly such as the pyramids shown. However, other shaped
features can be suitable for use in the present invention. This not
only increases surface area for exposure to light or other energy
sources, but also provides an increased junction surface area per
total area of the device. Further, the diamond-like carbon material
can have a surface roughness which further increases the surface
area on a much smaller scale than illustrated and than the pyramid
features. FIG. 4 is a micrograph of a diamond-like carbon material
suitable for use in the present invention illustrating random
asperities of typical amorphous diamond. The features can typically
have dimensions in the tens of microns range, while the
diamond-like carbon material can have asperities in the nanometer
range. In one aspect, the diamond-like carbon material can have an
average surface asperity having a height of from about 10 to about
10,000 nanometers. In another aspect, the diamond-like carbon
material can have an average asperity height of from about 10 to
about 1,000 nanometers. In yet another aspect, the average asperity
height can be about 800 nanometers. In a further aspect, the
average asperity height can be about 100 nanometers. Further, in
one aspect the asperity can have an average peak density of at
least about 1 million peaks per square centimeter of emission
surface. In another aspect, the average peak density can be at
least about 100 million peaks per square centimeter of the surface.
In yet another aspect, the peak density can be at least about 1
billion peaks per square centimeter of the surface. In a further
aspect, the average asperity can include a height of about 800
nanometers and a peak density of at least about, or greater than
about 1 million peaks per square centimeter of emission surface. In
yet a further aspect, the asperity can include a height of about
1,000 nanometers and a peak density of at least about, or greater
than 1 billion peaks per square centimeter of the surface.
[0064] Further, the diamond-like carbon material can be grown as a
polycrystalline film on a silicon substrate, preferably the (100)
face of a silicon wafer. By orienting the nuclei, forming
crystallographically oriented pits, and/or minimizing the growth
rate, the multiple grains can merge to form a mosaic structure
having similar orientations such that the overall crystal structure
is intermediate between single crystalline, which can be difficult
to achieve, and polycrystalline. FIG. 5 is a micrograph of such a
mosaic structure of diamond-like carbon grown hetero-epitaxially on
a 100 face of silicon.
[0065] As noted above, various dopants can enhance or control the
conductivity of the conductive diamond-like carbon materials of the
present invention. Most often suitable dopants can include B, N,
Si, P, Li, conductive metal, or combinations thereof, although
other materials can also be effective. Boron doped diamond-like
carbon materials can be highly transmissive and is also conductive.
For example, hydrogenated boron doped diamond-like carbon material
can be formed using a radio frequency chemical vapor deposition
process including a carbon source gas and a boron source gas.
Non-limiting examples of carbon sources gases can include methane
and ethylene. Similarly, non-limiting examples of boron source
gases can include BH.sub.3 and B.sub.2H.sub.2, although other boron
gases can be used. This hydrogenated boron doped diamond material
and other diamond-like materials of the present invention can serve
as a conductive layer, passivation layer, and an anti-reflection
layer. Thus, a conventional SiN anti-reflection layer can be
eliminated Similarly, passivation steps and techniques can be
reduced or entirely eliminated. The diamond-like carbon material
can enhance resistance to mechanical scratching and chemical
corrosion. Further, an optional metal material can be added during
formation of the boron doped diamond-like carbon material. For
example, a silver or other metal vapor can also be introduced
during vapor deposition.
[0066] Additionally, excessive grain boundaries within the
conductive diamond-like carbon material can increase resistivity of
the material. Grain boundaries can be minimized using a variety of
techniques. In one currently preferred approach, formation of the
diamond-like carbon material can be initiated using nanodiamond
seeding. Alternatively, high temperature annealing of the
diamond-like carbon material can help to reduce grain boundaries
somewhat. Further, surface roughness of the conductive diamond-like
carbon material can be less than about 30 nm This can be
accomplished using a suitable technique. For example, reverse
casting using a smooth inverse mold, polishing, or other similar
processes can be used. In yet another alternative aspect of the
present invention, the semiconductor layer can be prepared by
etching to roughen the n-doped surface of the semiconductor. This
can enhance diamond-like carbon grain growth and further increase
electron flow into the diamond-like carbon material layer.
[0067] In accordance with the present invention, an electronic
device can include a diamond-like carbon electronic cathode which
consists essentially of the conductive diamond-like carbon. This is
particularly useful in the context of forming solar cells. In this
manner, the solar cell cathode can exclude any metal grids or other
materials which contribute to decreases in transmissivity.
Conventional metal leads can be formed around the periphery of the
diamond-like carbon cathode which can be used to integrate the
electronic device as part of a complete circuit. Alternatively, or
in addition, the cathode can be formed by depositing diamond-like
carbon on a metallic layer such as silver grease or other suitable
conductive layer.
[0068] The conductive diamond-like carbon cathode or anode of the
present invention can have any functional thickness. However, the
cathode can typically have a thickness from about 0.01 .mu.m to
about 10 .mu.m. Thus, the overall device can, in some embodiments,
measure from about 10 .mu.m to about 350 .mu.m, and in some cases
from about 50 .mu.m to about 150 .mu.m.
[0069] Further, the anode can be formed of any suitable conductive
material. Non-limiting examples of suitable conductive materials
can include silver, gold, tin, copper, aluminum, and alloys thereof
Alternatively, at least a portion of the anode can be formed of a
conductive diamond-like carbon material. Although the same
parameters can be used as described above, transmissivity of the
anode is often less important. Therefore, a higher sp.sup.2 carbon
bonded content can be tolerated than for the cathode side without
the need for additives or dopants.
[0070] In another embodiment of the present invention, the charge
carrier separation layer can serve as one or more portions of a p-n
or p-i-n junction. For example, the charge carrier separation layer
can be p-doped while the conductive diamond-like carbon cathode can
be n-doped in a region adjacent the charge carrier separation
layer, as previously discussed. Thus, the charge carrier separation
layer would serve only as a single portion of the junction.
Similarly, the conductive diamond-like carbon cathode can include
multiple regions, e.g. a conductive electrode region remote or
opposite from the charge carrier separation layer and an n-doped
region proximate to the charge carrier separation layer.
[0071] In yet another detailed aspect of the present invention, the
charge carrier separation layer can form a multi-junction solar
cell. Multiple junctions can be configured having a variation in
bandgaps. Typically, a single junction is capable of absorbing
light corresponding to a specific bandgap for the materials
comprising the junction. By preparing and configuring multiple
junctions in series across the device each junction can have a
different bandgap. As a result, a larger percentage of incoming
energy can be converted to useful work, e.g. electricity. The
higher bandgap materials can be placed above, i.e. closer to the
cathode and light entry side, the lower bandgap materials. The
charge carrier separation layer can be multiple p-n and/or p-i-n
junctions to form a multi junction solar cell. The bandgap of each
layer can be adjusted by varying dopant concentration, type and/or
semiconductor material, e.g. silicon, gallium-based materials, or
the like. In order to fully take advantage of the multiple
junctions, the thickness is often maintained sufficiently thin to
allow at least some light to pass through each layer and the layers
can be formed of light transmissive materials as discussed
elsewhere.
[0072] Alternatively, the charge carrier separation layer can
include a compositionally graded material including carbon and
semi-conductor. This approach has the added advantage of reducing
thermal mismatch stresses between adjacent layers or by eliminating
distinct layers altogether. The charge carrier separation layer can
comprise a compositionally graded material of carbon and a
semi-conductor. For example, the charge carrier separation layer
can be graded from pure Si to SiC (e.g. in distinct layers of
10/20/30/40/50% Si or by a continuous gradation of materials) with
a SiC layer adjacent the conductive diamond-like carbon material of
the cathode. Optionally, each layer can be progressively doped
having higher bandgaps with higher carbon content. Compositional
differences can be achieved, for example, by varying gas source
concentrations or by varying impact energy on corresponding
sputtering targets.
[0073] In one aspect of the present invention, the graded material
can include at least four distinct compositionally graded layers.
Typically, from four to about ten graded layers and preferably four
to about six layers can be formed. Alternatively, full spectrum
solar cells utilizing indium gallium nitride may also be suitable
in connection with the present invention.
[0074] As an additional benefit of the present invention, each of
the cathode, anode and charge carrier separation layers can be
formed or prepared at a temperature below about 750.degree. C., and
preferably below about 650.degree. C. Such low temperature
processing can prevent or significantly reduce warpage.
Additionally, amorphous diamond has a high radiation hardness such
that it is resistant to aging and degradation over time. In
contrast, typical semiconductor materials are UV degradable and
tend to become less reliable over time. The use of amorphous or
diamond-like carbon material has the further advantage of reducing
thermal mismatch between layers of the device. For example,
silicon, silicon carbide and diamond-like carbon have a thermal
expansion coefficient of around 4 ppm/.degree. C. (near the process
temperatures used herein) which dramatically reduces thermal
mismatch stress during and after processing. This affect also
reduces delamination as substantially all of the layers of the
device can have substantially similar thermal expansion properties
such that during thermal cycling and extended use, interfaces
between layers retain interfacial strength. Solar cells formed in
accordance with the present invention can have conversion
efficiencies from about 18% to about 25%, although further improved
performances may be obtained by judicious optimization and choice
of materials based on the teachings herein. For example, graded
and/or multi-junction embodiments can potentially realize
efficiencies of up to about 10%, over conventional silicon solar
cell efficiencies which are currently about 15-18%.
[0075] Current silicon semiconductor based solar cells (single
crystal and polycrystalline) typically include a deep buried grid
of silver on the light absorption side and a full faced aluminum
layer intercepted by deep buried grid of silver on the back side.
As the silicon layer becomes thinner, the processing temperature
(e.g. 800.degree. C.) for sintering silver powder to form a
continuous mass and to diffuse silver across the anti-reflection
layer on the top, and aluminum layer on back can cause warping.
This is a result of the thermal expansion coefficient of silicon
being much lower than that of silver or aluminum However the CTE of
diamond-like carbon can be matched to that of silicon when the
conductive diamond-like carbon replaces aluminum. Because aluminum
generally covers the entire back side of the silicon layer, the
conductive diamond-like carbon does not distort the thin silicon
layer. Specifically, the silicon or semiconductor layer is not
processed at a conventional high temperature, e.g. around
800.degree. C. Further, diamond-like carbon can form an excellent
ohmic contact with silicon such that additional coating of silver
does not require a high temperature sintering of silver whereas
only low temperature sintering is needed, e.g. less than about
300.degree. C.
[0076] Further, solar cells formed in accordance with the present
invention can also include dye-sensitization such as by using
dye-sensitized metal oxides and/or a layer of spectral sensitizing
dye on a metal oxide semiconductor layer in accordance with known
dye sensitized solar cell technologies. In yet another aspect of
the present invention, the diamond-like carbon electronic device
can be configured as a fuel cell.
[0077] Further, the entire diamond-like carbon electronic device
can be a solid assembly having each layer in continuous intimate
contact with adjacent layers and/or members. The above-recited
components can take a variety of configurations and be made from a
variety of materials. Each of the layers can be formed using any
number of known techniques such as, but not limited to, vapor
deposition, thin film deposition, preformed solids, powdered
layers, screen printing, or the like. In one aspect, each layer is
formed using vapor deposition techniques such as PVD, CVD, or any
other known thin-film deposition process. In one aspect, the PVD
process is sputtering or cathodic arc.
[0078] Those of ordinary skill in the art will readily recognize
other components that can, or should, be added to the assembly of
FIG. 2 in order to achieve a specific purpose, or make a particular
device. By way of example, without limitation, a connecting line
can be placed between the anode and the cathode to form a complete
circuit and allow electricity to pass that can be used to power one
or more devices (not shown), or perform other work.
[0079] In an optional step, the diamond-like carbon electronic
devices can be heat treated in a vacuum furnace. Heat treatment can
improve the thermal and electrical properties across the boundaries
between different materials. The diamond-like carbon electronic
device can be subjected to a heat treatment to consolidate
interfacial boundaries and reduce material defects. Typical heat
treatment temperatures can range from about 200.degree. C. to about
800.degree. C. and more preferably from about 350.degree. C. to
about 500.degree. C. depending on the specific materials
chosen.
[0080] The following are examples illustrate various methods of
making electronic devices in accordance with the present invention.
However, it is to be understood that the following are only
exemplary or illustrative of the application of the principles of
the present invention. Numerous modifications and alternative
compositions, methods, and systems can be devised by those skilled
in the art without departing from the spirit and scope of the
present invention. The appended claims are intended to cover such
modifications and arrangements. Thus, while the present invention
has been described above with particularity, the following Examples
provide further detail in connection with several specific
embodiments of the invention.
EXAMPLE 1
[0081] FIG. 3 illustrates a graded solar cell in accordance with
the present invention. A chemical vapor deposition silicon film 40
of about 10 .mu.m having micron grains serves as the photoelectric
substrate. The silicon film is coated successively with
silicon-carbon layers via chemical vapor deposition. Layers 42, 44,
46, 48 and 50 have a Si:C ratio of 10:90, 20:80, 30:70, 40:60 and
50:50 (SiC), respectively. Each layer is doped such that the graded
portion represents a single p-n junction. A conductive diamond-like
carbon film 52 having a thickness of about 10 .mu.m is deposited on
the SiC layer 50. The diamond-like carbon is deposited at partial
vacuum of acetylene gas and 13.6 MHz to form the conductive
diamond-like carbon which is also light transmissive. The resulting
solar cell has layers having bandgaps from 1.1 eV for silicon to
3.3 eV for silicon carbide which covers most visible light, e.g.
red about 1 eV while blue is about 3 eV.
[0082] Of course, it is to be understood that the above-described
arrangements are only illustrative of the application of the
principles of the present invention. Numerous modifications and
alternative arrangements may be devised by those skilled in the art
without departing from the spirit and scope of the present
invention and the appended claims are intended to cover such
modifications and arrangements. Thus, while the present invention
has been described above with particularity and detail in
connection with what is presently deemed to be the most practical
and preferred embodiments of the invention, it will be apparent to
those of ordinary skill in the art that numerous modifications,
including, but not limited to, variations in size, materials,
shape, form, function and manner of operation, assembly and use may
be made without departing from the principles and concepts set
forth herein.
* * * * *