U.S. patent application number 13/105045 was filed with the patent office on 2011-11-10 for formation of selenide, sulfide or mixed selenide-sulfide films on metal or metal coated substrates.
This patent application is currently assigned to University of Delaware. Invention is credited to Erten Eser, Shannon Fields.
Application Number | 20110272787 13/105045 |
Document ID | / |
Family ID | 36228250 |
Filed Date | 2011-11-10 |
United States Patent
Application |
20110272787 |
Kind Code |
A1 |
Eser; Erten ; et
al. |
November 10, 2011 |
FORMATION OF SELENIDE, SULFIDE OR MIXED SELENIDE-SULFIDE FILMS ON
METAL OR METAL COATED SUBSTRATES
Abstract
A composition for preventing cracking in composite structures
comprising a metal coated substrate and a selenide, sulfide or
mixed selenidesulfide film. Specifically, cracking is prevented in
the coating of molybdenum coated substrates upon which a copper,
indium-gallium diselenide (CIGS) film is deposited. Cracking is
inhibited by adding a Se passivating amount of oxygen to the Mo and
limiting the amount of Se deposited on the Mo coating.
Inventors: |
Eser; Erten; (Newark,
DE) ; Fields; Shannon; (Wilmington, DE) |
Assignee: |
University of Delaware
Newark
DE
|
Family ID: |
36228250 |
Appl. No.: |
13/105045 |
Filed: |
May 11, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11577777 |
Jul 29, 2008 |
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PCT/US05/37711 |
Oct 21, 2005 |
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13105045 |
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60620352 |
Oct 21, 2004 |
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Current U.S.
Class: |
257/613 ;
257/E29.079 |
Current CPC
Class: |
C23C 14/20 20130101;
C23C 26/00 20130101; C23C 14/562 20130101 |
Class at
Publication: |
257/613 ;
257/E29.079 |
International
Class: |
H01L 29/24 20060101
H01L029/24 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was developed under a grant no.
AdJ-1-30630-12 from the National Renewable Energy Laboratories.
Claims
1-19. (canceled)
20. A metal-coated substrate with a CuInGaR.sub.2 film on a surface
of the metal coating, wherein R is Se or a combination of Se and S,
wherein the metal coating contains oxygen in an amount sufficient
to inhibit reaction of the metal with Se, and wherein the metal is
selected from the group consisting of Mo, W, Cr, Ta, Nb, V and
Ti.
21. The metal-coated substrate according to claim 20 wherein the
amount of oxygen is 6-8 atomic percent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional application of application
Ser. No. 11/577,777 filed on Apr. 23, 2007, which is a U.S.
National Phase filing of PCT International Application No.
PCT/US2005/037711 filed on Oct. 21, 2005, which claims the priority
benefit of U.S. Provisional Application No. 60/620,352 filed on
Oct. 21, 2004; the entire contents of all of which are hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0003] The invention is directed to a new process and a new
composition of matter. It deals with the formation of selenide,
sulfide, and mixed selenide-sulfide on metal or metal coated
substrates requiring temperatures in excess of 200.degree. C.
Specifically, it solves the problem of crack formation which
commonly occurs when copper, indium, gallium, diselenide, i.e.,
CuInGaSe.sub.2 (CIGS) is deposited onto a molybdenum coated
substrate. It also improves the adhesion of the CIGS film to the Mo
layer. In the past, both of these issues have impeded the
development of CIGS based photovoltaic (PV) devices on flexible
polymer substrates.
[0004] In a more general way, the invention also applies to other
substrates as well, such as Mo coated glass and Mo coated metal
foils, as well as glass, polymer and metal foil substrates coated
with niobium (Nb), tantalum (Ta), tungsten (W), titanium (Ti), for
example. The invention further applies to methods of forming CIGS
films by selenization of precursors films. Such precursor films can
include metals or compounds in the form of uniform layers or
powders as long as the selenide, sulfide or mixed selenide-sulfide
is formed on metal film such as, for example, Mo, Ta, W, and TI. In
cases where selenide or mixed selenide-sulfide films are formed
directly on metal foils, the invention improves the adhesion of the
film to the substrate.
[0005] An example of the cracking found in prior art composite
films can be seen in the Scanning Electron Microscopy (SEM)
micrograph shows in FIG. 1 where the CIGS layer (white area) was
deposited on a Mo film (dark area) which coated a polyimide film.
Such cracks dramatically reduce the performance of CIGS based PV
devices. This consequently is illustrated in FIGS. 2a and 2b. FIG.
2a is the photograph of a sample containing 4 devices. On the same
there are two orthogonal contact lines (labeled 1 and 2 in FIG.
2.2a) to the underlying Mo film that is the electrical back contact
to the devices. FIG. 2b gives the current density vs voltage (JV)
characteristics of one of the devices utilizing one and both of the
contact lines. When only the contact line 1 is used, current
collection from the device is severely limited compared to the case
when contact line 2 is placed orthogonal to line 1. The explanation
for this is that, in this particular case, the cracks are mostly
parallel to contact line 1 and therefore current can't be collected
by the contact line 1 alone.
[0006] U.S. Pat. Nos. 6,310,281 B1 and 6,372,538 B1 dated
respectively Oct. 30, 2001 and Apr. 16, 2002 allege that during the
fabrication of CIGS photovoltaic modules on polyimide substrates,
cracking of sputter deposited Mo layer during subsequent downstream
processing can be avoided by the addition of oxygen or water vapor
into the sputtering gas. These disclosures allege that as a result
of this addition of oxygen or water vapor into the sputtering gas,
oxygen is entrained into the Mo layer creating a higher level of
internal compressive stress in the Mo layer as a result of which
"these layers are able to tolerate temperature changes that occur
in subsequent processing without suffering temperature-induced
cracking and fracturing." However, these patents fail to state the
amount of oxygen entrained into the films, and instead, give the
range of the relative amount of water vapor or oxygen in the
sputtering gas. The amount of oxygen in the Mo is intimately
related to the design and operation of the sputtering system used
for the deposition of Mo layers. These patents do not suggest an
amount of oxygen concentration in the Mo film which is necessary to
suppress the cracking of such films during the fabrication of CIGS
photovoltaic modules. Indeed, studies to the issuance of these
patents have concluded without exception, that Mo cracking is an
unresolved problem.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention is at least based on the discovery
that the root cause of the cracking in Mo films is a chemical
reaction with Se, which reduces the yield strength of the film.
Consequently, this invention utilizes means for inhibiting this
chemical reaction by limiting the exposure of the Mo film to Se and
by incorporating oxygen into the Mo at concentrations high enough
to passivate against reaction with Se.
[0008] Thus, the invention comprises new compositions of matter and
a process which includes inhibiting the reaction of Mo with Se
during the formation of CIGS films. For example, with reference to
the vapor disposition of CIGS films on a Mo coated substrate in a
roll-to-roll system, the process of this invention comprises:
[0009] providing a substrate which is coated with Mo containing a
sufficient amount of oxygen to passivate against Se,
[0010] introducing the Mo coated substrate into a chamber means for
vapor depositing Se, Cu, In, Ga fluxes onto the surface of the Mo
coating, said chamber means containing a separate, substantially
isolated vapor deposition zone,
[0011] simultaneously depositing Se, Cu, In and Ga onto the Mo
coated substrate within the deposition zone,
[0012] limiting the amount of Se deposited on the Mo coated
substrate to only that amount required to form a CIGS film
thereon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a SEM micrograph showing cracks on both Mo film
(dark area) and on the CIGS layer (bright area);
[0014] FIG. 2a is a photograph of a sample with 4 CIGS devices
fabricated on a cracked Mo back contact;
[0015] FIG. 2b shows a JV characteristic of one of the devices in
utilized back contact 1 alone and 1 and 2;
[0016] FIG. 3 is a roll-to-roll reactor for the physical vapor
deposition of CIGS films onto a web type substrate;
[0017] FIG. 4a is an exploded schematic view of the web guide;
[0018] FIG. 4b is a schematic view of the web guide with upper and
lower sections fitted together;
[0019] FIG. 5 is a schematic of a Se/S source; and
[0020] FIG. 6a is an auger depth profile of reference Mo film
TM24312.2B.
[0021] FIG. 6b is an auger depth profile of a film TM 24961.1
having low web tension.
[0022] FIG. 6c is an auger depth profile of a film TM24961.2 with
5% oxygen over the second target.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] The invention is based on a set of experiments. During these
experiments CIGS films were deposited, in a roll-to-roll deposition
reactor, on Mo coated Upilex-S polyimide web. These experiments
compared the Mo cracking and adhesion of the CIGS films to Mo for
depositions performed under conditions of high and a factor of 10
lower levels of selenium (Se) vapor. Table I summarizes these
results and also gives the composition of the CIGS films.
[0024] Consumption of Se was estimated by measuring Se level in the
source before and after certain number of runs. Adhesion results
were estimated from the amount of film lifted off by 40 oz/'' tape.
In order to evaluate cracking of Mo under the CIGS a 1''.times.1''
sample was cut and CIGS was removed from the corners. Then indium
solder was placed over the four corners. Resistance between two
diagonal corners relative to the same resistance on the unprocessed
Mo coated Upilex-S gives an indication of the severity of cracking.
It should be pointed out that even though resistance of the Mo film
was used to quantify the degree of cracking, these cracks are
visually observable since they in turn cause the cracking of the
CIGS film deposited over the Mo layer. In evaluating cracking and
adhesion it is prudent not to take into account the runs grayed in
the Table I because of the large compositional deviations in the
films from single phase CIGS.
[0025] Examination of the data in the Table I show that reducing
the amount of Se co-evaporated along with copper (Cu), indium (In),
and gallium (Ga) while still maintaining enough to form the CIGS
compound, reduces crack density on the Mo layer and improves
adhesion of the CIGS film to Mo layer. The process seems to be the
chemical reaction of the excess Se with Mo structurally weakening
Mo layer and thus causing cracking due to stresses associated with
roll-to-roll processing of flexible web. Mo--Se reaction also seems
to result in reducing adhesion of CIGS to Mo probably as a
consequence of the formation of structurally weak reaction
by-products at the interface.
TABLE-US-00001 TABLE I Cracking and CIGS/Mo adhesion of CIGS films
deposited under different Se consumption levels. CuInGaSe.sub.2
Film Composition Run Cu In Ga Se Cu/ Ga/ Cracking Adhesion # Date
Substrate (at %) (at %) (at %) (at %) In + Ga In + Ga Diag. R
(.OMEGA.) 40 oz/'' tape Se operation Comments 70209 May 16, 2003
TM23930.A 24.6 19.7 6.6 49.1 0.94 0.25 348 poor source full @ 70210
May 19, 2003 TM23930.A 24 19.3 7.4 49.3 0.90 0.28 721 poor start
same as 70211 May 21, 2003 TM23930.A 27.5 24.9 10.5 37.2 0.78 0.30
2 NA 209 same as 209. No 1st pass. Source 30 mm below top @ end. 10
to 12 mm/ run consumption 70213 May 27, 2003 TM23930.A 22.9 21.7
5.8 49.7 0.83 0.21 412 poor same as 209 70215 Jun. 9, 2003
TM23930.A 25.1 19 7.6 48.3 0.94 0.29 6 good source full new Cu @
start 70216 Jun. 18, 2003 TM23930.B 42.8 12 4.3 40.9 2.63 0.26 9
good same as 215 boat ab- ort after 30 min 70217 Jun. 20, 2003
TM23930.B 26.7 20.4 4.5 48.5 1.07 0.18 57 good same as 215 70218
Jun. 25, 2003 TM23940.B 23.5 20.7 6.3 49.5 0.87 0.23 461 good same
as 215 70219 Jul. 1, 2003 TM23940.B 16.3 24.29 6.5 52.9 0.53 0.21
955 good same as 215.5 mm below top @ end. 1 mm/run consumption
Note: Diagonal resistance on the Mo coated substrates prior to
CuInGaSe.sub.2 deposition measured around 2 .OMEGA..
[0026] FIG. 3 shows schematically a roll-to-roll reactor for the
physical vapor deposition of CIGS films onto a web type substrate
that incorporates the methods described above. The reactor is
divided into three regions. Region 100 contains evaporation sources
and is isolated from the other regions except for the rectangular
deposition zone opening (10) where the evaporation materials
condense on the web and the pumping port (20) connecting Region 100
to the vacuum pump. Web transport (30) and heating components (40)
are located in Region 200. In addition, a web guide (50) is also
located in Region 200 positioned right over the deposition zone.
The web guide, shown in more detail in FIG. 4, serves multiple
operational purposes. It has an upper section (52) and a lower
section (54) that snugly fit each other forming a rectangular
tunnel, slightly larger in width than the web, through which the
web substrate is transported. The height of the tunnel is no larger
than twice the substrate thickness. The guide's lower section has
an opening (56) that is aligned with the deposition zone opening
(1) of FIG. 3. The holes (58) on the sides of the lower section of
the web guide are for temperature sensors, such as thermocouples,
for the measurement and control of the web temperature. The
sections of the web guide extending upstream and downstream from
the deposition zone serves to create very low gaseous conductance
to isolate Region 100 from Region 200 and therefore minimize the
leakage of Se/S into the Region 200. It is preferred to have the
web guide made out of an infrared (IR) transmitting glass such as
Vicor or quartz so that it doesn't interfere with the heating of
the web substrate. It is also preferred to have all the surfaces of
the web guide "flame polished" to reduce the risk of damaging the
substrate and to reduce the risk of breakage of the guide itself
during heating and/or cooling. Another advantage of using glass as
the material of construction for the web guide is its inertness
towards reaction with Se and/or S. As a result, periodic
maintenance cleaning of the guide will be relatively easier.
Another advantage of the web guide is the fact that it acts as a
support for the web. In the case of high throughput processing, web
speed has to be increased. In order to keep CIGS film thickness
unchanged it is necessary to increase the deposition zone length to
accommodate larger number of sources. Under these conditions the
sagging of the web is unavoidable and becomes a problem. However,
this problem is avoided when a web guide is used, since the guide
supports the weight of the web during its transition through the
deposition zone.
[0027] In order to further reduce the leakage of Se/S from Region
100 into Region 200 a gas purge is established in Region 200. A
flow of gas is introduced into the Region 200 through inlets (6)
and is pumped out through pumping holes (70) into Region 300 as
shown in FIG. 3. The flow rate and the conductance of the holes
(70) are adjusted to provide an excess of pressure in Region 200
relative to Region 100. Region 300 would contain all other
components required for the operation of the system.
[0028] For such a system to operate efficiently it is necessary to
accurately control Se effusion rate and keep it to a minimum level
as required by the formation of the CIGS film on the moving
substrate. This requires an accurate control of the surface
temperature of the liquid Se (or S) in the source, which in turn
sets the vapor pressure in the source above the melt. Se/S have
high vapor pressures at moderately low temperatures such that
operational surface temperatures are expected to be in the range of
200.degree. C. to 400.degree. C. and should be colder than the
upstream delivery manifold to avoid condensation therein. This high
temperature manifold provides an uncontrollable heat flow into the
source. FIG. 5 shows schematically a Se/S source 80 that provides a
workable solution to the difficulties mentioned above. The surface
temperature of the melt is measured and controlled by the sheathed
thermocouple (82) attached to a ring shaped float (84). In this
way, irrespective of the melt level, thermocouple (852) always
indicates the melt surface temperature. The float material can be
glass or graphite and can have a sealed internal cavity to increase
buoyancy especially in the case of S evaporation. Cooling coil (86)
through which water flows at controlled rates provides adjustable
heat removal to balance heat load to the source mainly through the
manifold. The system is then able to control low melt surface
temperatures by the external heater (88) with feedback from
thermocouple (82).
[0029] Methods that would inhibit the reaction of Mo with Se are
based on the principle that reactivity of Mo to Se can be
suppressed by adding oxygen in sufficient concentrations to Mo. The
reason behind this approach is that the Gibbs free energy of the
reaction of Mo with oxygen is lower than the Gibbs free energy of
the reaction of Mo with Se or S. For illustration purposes Gibbs
free energy for some of the selenization, sulfurization and
oxidation reactions of Mo at 700 K (427.degree. C.) are given
below:
TABLE-US-00002 Mo + Se.sub.2 = MoSe.sub.2 .DELTA.Grx = -164 kJ/mol
Mo + 1/4Se.sub.8 = MoSe.sub.2 .DELTA.Grx = -142 kJ/mol 3Mo +
2Se.sub.2 = Mo.sub.3Se.sub.4 .DELTA.Grx = -363 kJ/mol Mo + S.sub.2
= MoS.sub.2 .DELTA.Grx = -270 kJ/mol Mo + 1/4S.sub.8 = MoS.sub.2
.DELTA.Grx = -249 kJ/mol 2Mo + 3/2S.sub.2 = Mo.sub.2S.sub.3
.DELTA.Grx = -403 kJ/mol Mo + 3/2O.sub.2 = MoO.sub.3 .DELTA.Grx =
-566 kJ/mol Mo + O.sub.2 = MoO.sub.2 .DELTA.Grx = -467 kJ/mol
[0030] These reaction energies imply that Mo films may be
passivated against Se and/or S by introducing an appropriate amount
of oxygen into the Mo film. The amount of oxygen in the Mo film has
to be larger than a minimum level to be effective in passivating
against chemical reactions with Se and/or S. Passivation against Se
and against S would require different minimum level of oxygen in
the film. As will be described later (paragraph B3), in the case of
Mo sputter-coated polyimide substrates, 3 to 4 atomic percent
oxygen was found to be inadequate for passivation against Se and
thus resulted in cracking of Mo film and low adhesion of the CIGS
film to Mo. However, 6 to 8 atomic percent oxygen prevented Mo
cracking and resulted in better adhesion of CIGS film to Mo.
[0031] Oxygen will also passivate other metal films such as
tungsten (W), chromium (Cr), tantalum (Ta), niobium (Nb), vanadium
(V), titanium (Ti), and others susceptible to reaction with
selenium and/or sulfur during deposition of selenide, sulfide, and
mixed selenide/sulfide films on them. This is because oxidation
reactions have lower Gibbs free energy than the selenization or
sufurization reactions. However, the minimum oxygen level for
passivation would be different for different metal films.
[0032] Method of forming the metal films would also control the
minimum oxygen level for passivation as they would give different
structures to the films. It should also be emphasized that the type
of the selenide, sulfide, and the mixed selenide/sulfide film and
the method of forming it will affect the minimum oxygen level for
passivation. Therefore, in general, the minimum oxygen level for
passivation has to be determined experimentally in each case.
[0033] Any method can be used to introduce oxygen into the metal
films as long as it does not degrade operational characteristics of
the films that would be defined by the user. In the case of Mo
films or other films of refractory metals, the preferred method of
film forming being sputtering, the oxygen can be introduced by
mixing oxygen gas or other oxygen containing gas to the sputtering
gas such as argon. The percentage of the oxygen or oxygen
containing gas in the sputtering gas has to be determined
experimentally to give the desired oxygen level in the Mo film.
This is because the amount of oxygen in the sputtering gas mixture
is not sufficient, by itself, to determine the oxygen concentration
in the metal film. In fact, for a given gas concentration, the
amount of oxygen in the film can differ greatly from one system to
another.
[0034] Since the purpose of oxygen is to passivate Mo film against
reaction with Se and/or S it would be sufficient to oxygenate the
top portion of the film in order to achieve the desired effect
rather than introduce oxygen throughout the thickness of the metal
film. As will be shown in Section B3, oxygenation of the top 1000
.ANG. of 2000 .ANG. Mo film was adequate for the passivation of the
entire film. In this instance, as well, the thickness of the
oxygenated top layer need be determined experimentally. It should
be pointed out that oxygenated top layer need not be deposited at
the same time and in the same reactor as the non-oxygenated bottom
portion of the metal film.
[0035] In the case of polyimide films, which always contain a
certain percentage of water, the metal film can be passivated by
allowing the polyimide be heated naturally by the sputtering
plasma. In this case, the water in the polyimide outgases during
the deposition of the metal thus providing the oxygen necessary for
passivation. It will be shown in Section B3 that this method of
oxygenation also gave satisfactory results.
[0036] The invention identifies reaction between Se/S and metal
film substrate as being detrimental to the mechanical integrity
(i.e. cracking) of both the metal and selenide/sulfide films and
also being the cause of reduced adhesion between the metal and the
selenide/sulfide films. It solves these problems by suppressing the
reaction between the metal film and Se/S through process related
techniques and through the addition of oxygen, above a certain
minimum level, into the metal film passivating it against reaction
with Se/S.
[0037] Present technology doesn't provide a solution to the
cracking of metal and selenide/sulfide films. In fact, at the
present time, the technology favors an oversupply of Se/S during
the formation of the selenide/sulfide films aggravating the
problem.
[0038] Applications could extend beyond photovoltaics where
selenide and/or sulfide films are deposited on metal and metal
coated substrates. Also, web guide/sealing assembly can be used in
any web coating application to seal the web transport section from
the coating section.
[0039] Following is the summary of the experiments testing the
invention.
[0040] A Upilex S polyimide sputter coated with Mo was used in a
roll-to-roll CIGS deposition process. The sputter deposition system
which produced such a product consists of two targets 3 inches
apart facing a web carrier drum over which polyimide web is
stretched. The drum rotates in synchronization with the web
translation to avoid sliding of the web over its surface. Heating
of the web due to the sputtering plasmas is limited due to the drum
acting as a heat sink. The drum can be actively refrigerated to
further limit web temperature, though in the present this was not
the case. All the Mo films discussed here are approximately 2000
.ANG. thick. This initial material showed substantial cracking
during the deposition of CIGS films. Subsequently Mo deposition
conditions were modified to obtain a Mo film that would not crack
during CIGS deposition. Two Mo runs on Upilex S were conducted
under the same conditions as a previous deposition, identified as
TM24312.2B, which resulted in heavy film cracking, except for two
changes. In the first run the web tension was reduced as much as
possible allowing the web temperature to rise. In the second case,
5% oxygen was introduced into the sputtering gas directed onto the
second target from which top half of the total Mo thickness is
deposited. These two runs were identified as TM24961.1 and
TM24961.2 respectively.
[0041] CIGS films were deposited on these substrates in an inline
reactor. The composition of the CIGS films were found to be
similar, as shown in Table 3.1, but the film on substrate
TM24312.2B showed cracking while films on substrates TM24961.1 and
TM24961.2 had no observable cracks.
TABLE-US-00003 TABLE 3.1 Composition of CIGS Mo coated films
deposited on different Upilex S substrates. Cu In Ga Se Run (at (at
(at (at Cu/ Ga/ # Substrate %) %) %) %) In + Ga In + Ga 70227
TM24312.2B 24.0 21.0 6.1 48.8 0.89 0.23 70261 TM24961.1 24.2 17.9
8.7 49.3 0.91 0.33 70262 22.0 18.2 8.2 51.6 0.83 0.31 70264
TM24961.2 24.0 18.5 8.0 49.6 0.91 0.30 70265 24.4 18.7 7.6 49.3
0.93 0.29
[0042] Auger depth profiles of these three Mo films are shown in
FIGS. 6a-6c and highlight the differences in the oxygen content. In
the case of the reference film, TM24312.2B, the oxygen content of
the film is between 2 to 3 at % in the top and bottom half of the
film corresponding to the deposition from the second and first
target respectively. Oxygen peak of in the middle of the film
corresponds to the gettering of background oxygen by the freshly
deposited film during transit between the two targets. The peak
concentration doesn't have much meaning since the depth resolution
in the data is rather poor.
[0043] Mo film TM24961.1 shows qualitatively the same oxygen
distribution but the amount of oxygen in the top and bottom half of
the film is approximately around 7 at %. The source of this oxygen
is water desorbing from the polyimide as a result of heating by the
sputtering plasmas due to the fact that there is very little heat
removal by the backing drum because of the low web tension. Again
there is an oxygen peak in the middle of the film due to the
gettering by the freshly deposited 1.sup.st half of the film.
[0044] Mo film TM24961.2 again has qualitatively similar oxygen
distribution but in this case there is an intentional injection of
oxygen onto the second target. As a result in the top half of the
film, oxygen concentration is around 8 at % while in the bottom
half is around 4 at % closer to the value in the reference film.
Again there is a peak in the oxygen distribution in the middle of
the film.
[0045] The absence of any observable film cracking on substrates
TM24961.1 and TM24961.2 is associated with the adequate oxygen
concentrations in the Mo films, which in the present case is around
6 to 8 at %. Based on the data from the reference film 3 at %
oxygen is not enough to suppress cracking. It is important to point
out that 8 at % oxygen in the top half of the film while the bottom
half has 4 at % suppresses the crack formation. This is an
indication that the process of crack formation involves the top of
the Mo film rather than the full thickness of the film.
[0046] Table 3.2 gives the device performance data on the CIGS
solar cells fabricated on the materials discussed above. Data
convincingly shows that, devices fabricated on oxygen containing Mo
films outperform the ones fabricated on the reference Mo. This is
not surprising in view of the film cracking observed on the
latter.
TABLE-US-00004 TABLE 3.2 Solar cell parameters of the CIGS devices
on TM24312.2B, TM24961.1 and TM24961.2 substrates Eff FF Voc Jsc
Roc Gsc Sample # Cell # Substrate (%) (%) (V) (mA/cm2)
(.OMEGA.-cm2) (mS/cm2) 70227.211 1 TM24312.2B 2.1 23.7 0.407 22.1
24.1 42.3 2 2.7 26.9 0.423 23.7 17.0 36.3 3 1.7 22.6 0.368 21.0
21.4 56.4 4 2.5 25.2 0.403 24.9 18.5 45.2 70227.212 1 2.2 24.1
0.384 23.5 22.2 46.7 2 2.7 25.4 0.409 25.8 17.1 44.0 3 2.3 26.4
0.361 24.3 18.2 40.4 4 2.6 26.0 0.391 25.8 15.8 46.5 70227.221 1
1.9 22.0 0.409 21.6 23.8 54.1 2 2.1 23.1 0.414 22.3 20.7 51.0 3 2.0
22.6 0.394 22.9 22.9 48.8 4 2.3 24.1 0.423 22.9 22.5 39.8 70227.222
1 1.7 22.3 0.373 20.3 24.0 52.2 2 2.1 22.8 0.403 23.0 19.7 54.5 3
2.2 23.5 0.391 24.2 19.4 50.6 4 2.3 22.9 0.402 24.8 18.4 54.8
70261.12A 1 TM24961.2 10.4 58.0 0.536 33.5 4.3 0.9 2 10.3 58.9
0.537 32.6 3.9 11.0 3 11.0 61.7 0.537 33.1 3.7 2.2 4 10.8 61.2
0.536 33.0 3.6 2.1 70261.12B 1 8.8 51.3 0.530 32.5 5.9 3.8 2 9.0
50.6 0.527 33.6 5.6 7.4 3 9.4 55.1 0.535 32.0 5.5 2.9 4 9.2 52.4
0.527 33.4 5.4 7.2 70262.22A 1 8.4 49.7 0.512 33.0 6.9 3.4 2 8.7
52.1 0.509 32.7 6.2 2.9 3 3.0 25.1 0.502 23.9 21.2 30.2 4 9.3 53.3
0.515 33.7 6.3 1.6 70262.22B 1 8.2 47.5 0.517 33.3 7.8 3.1 2 8.0
49.5 0.512 31.7 7.4 2.5 3 9.0 52.4 0.514 33.5 6.8 4.2 4 8.7 52.9
0.510 32.4 6.7 3.0 70264.21 1 TM24961.1 9.4 56.5 0.508 32.6 4.4 1.6
2 9.8 57.7 0.509 33.5 4.2 2.0 3 10.1 60.5 0.509 32.7 3.7 4.8 4 10.0
58.8 0.510 33.3 3.9 3.5 70264.22 1 9.1 54.8 0.505 32.7 5.3 5.8 2
9.4 56.3 0.509 32.9 4.7 0.6 3 8.4 52.1 0.508 31.8 5.4 2.4 4 8.1
50.4 0.501 32.1 5.6 7.7 70265.12 1 10.5 63.6 0.500 33.0 2.8 5.6 2
10.6 63.8 0.504 32.9 2.8 5.0 3 10.7 65.8 0.499 32.5 2.4 0.8 4 10.8
65.9 0.502 32.6 2.4 4.0 70265.22 1 10.5 63.2 0.503 33.0 3.0 3.7 2
10.5 63.5 0.505 32.8 3.0 2.7 3 10.1 62.3 0.508 32.0 3.0 4.1 4 9.8
60.7 0.503 32.2 3.2 1.9 70265.32 1 10.0 60.9 0.505 32.6 3.5 12.2 2
10.2 62.0 0.504 32.7 3.3 2.8 3 10.1 62.9 0.502 32.0 3.2 5.0 4 10.5
63.9 0.505 32.5 2.9 3.4 70265.42 1 9.8 60.0 0.502 32.6 3.9 1.3 2
10.0 61.1 0.501 32.8 3.5 6.4 3 9.9 62.2 0.501 31.9 3.3 1.2 4 10.3
63.3 0.502 32.2 3.0 2.5 70265.52 1 9.1 55.3 0.502 32.8 5.5 1.3 2
9.6 58.2 0.500 32.9 4.4 2.0 3 9.6 58.5 0.500 32.8 4.8 4.1 4 10.1
61.0 0.501 33.1 3.8 5.7 70265.62 1 7.6 46.0 0.517 31.9 13.2 8.4 2
7.7 48.3 0.516 31.1 11.4 4.6 3 8.5 51.9 0.518 31.5 10.5 0.7 4 8.7
53.1 0.518 31.7 9.2 3.8 70265.72 1 5.6 35.4 0.528 29.9 36.0 4.5 2
6.2 38.8 0.529 30.3 31.7 6.1 3 5.5 37.2 0.524 28.2 40.3 8.4 4 6.7
41.9 0.531 29.9 30.6 5.1
[0047] The foregoing description of the invention illustrates and
describes the present invention. Additionally, the disclosure shows
and describes only the preferred embodiments of the invention in
the context of a formation of selenide, sulfide or mixed
selenide-sulfide films on metal or metal coated substrates, but, as
mentioned above, it is to be understood that the invention is
capable of use in various other combinations, modifications, and
environments and is capable of changes or modifications within the
scope of the inventive concept as expressed herein, commensurate
with the above teachings and/or the skill or knowledge of the
relevant art. The embodiments described hereinabove are further
intended to explain best modes known of practicing the invention
and to enable others skilled in the art to utilize the invention in
such, or other, embodiments and with the various modifications
required by the particular applications or uses of the invention.
Accordingly, the description is not intended to limit the invention
to the form or application disclosed herein. Also, it is intended
that the appended claims be construed to include alternative
embodiments.
* * * * *