JP2003318424A - Thin film solar battery and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively diffuse alkali element to a light absorbing layer with higher efficiency during the heat treatment to effectively improve energy conversion in the manufacturing process of a thin film solar battery wherein the CIGS- system light absorbing layer is formed by forming a back electrode on a substrate, forming a precursor film on the back electrode and executing the heat treatment under the Se atmosphere, and a transparent electrode is formed, via a buffer layer, on the light absorbing layer. <P>SOLUTION: In the method of manufacturing thin film solar battery, an alkali element is diffused respectively to the light absorbing layer from the substrate including alkali element and an alkali layer provided between the back electrode and precursor film. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film solar cell using a compound semiconductor and a method for manufacturing the same.

[0002]

2. Description of the Related Art FIG. 1 shows a basic structure of a thin film solar cell using a general chalcopyrite compound semiconductor. That is, a Mo electrode 2 serving as a back surface electrode (plus electrode) is formed on an SLG (soda lime glass) substrate 1,
A light absorbing layer 5 is formed on the Mo electrode 2, and a transparent electrode 7 made of ZnO: Al or the like serving as a negative electrode is formed on the light absorbing layer 5 via a buffer layer 6 made of ZnS, CdS or the like. ing.

As the light absorption layer 4 in the thin film solar cell made of the compound semiconductor, Cu, (In, G) is currently used as a material that can obtain a high energy conversion efficiency exceeding 18%.
a), a CIGS thin film of Ib-IIIb-VIb2 group Cu (In + Ga) Se2 based on Se is used.

Conventionally, as a method for producing a light absorption layer by a CIGS thin film, a selenization method in which a metal precursor (precursor) thin film is used to produce a Se compound by a thermochemical reaction using an Se source such as H 2 Se gas is used. is there.

US Pat. No. 4,798,660 discloses
Back electrode by DC magnetron sputtering →
A metal thin film layer formed by stacking a pure Cu single layer → a pure In single layer in this order is selenized in an Se atmosphere, preferably H2Se gas, to form a light absorption layer composed of a CIS single phase having a uniform composition. It is disclosed.

Japanese Patent Application Laid-Open No. 10-135495 discloses that
As the metal precursor, there is shown one having a laminated structure of a metal thin film sputter-deposited using a Cu—Ga alloy target and a metal thin film sputter-deposited using an In target.

As shown in FIG. 2, when forming the light absorption layer 5 of the CIGS thin film on the Mo electrode 2 formed on the SLG (soda lime glass) substrate 1,
First, the Cu-Ga alloy layer 31 is formed by the first sputtering process SPT-1 using the Cu-Ga alloy target T2, and then the In-process is performed by the second sputtering process SPT-2 using the In target T1. Deposit layer 32,
The laminated precursor 3 including the Cu—Ga alloy layer 31 and the In layer 32 is formed. Then, the heat treatment step H
In the EAT, the laminated precursor 3 is heat-treated in the Se atmosphere to form the light absorption layer 5 of the CIGS thin film.

However, the Cu--Ga alloy layer 31 and the In layer 3
To form the precursor 3 having a laminated structure with
At the time of film formation or stock, the alloying reaction due to solid layer diffusion (diffusion between solids) proceeds at the interface of the lamination, and Cu-
An In-Ga ternary alloy is formed. In addition, the alloying reaction also proceeds in the Se step that is performed later.
It is difficult to uniformly control the progress of the alloying reaction at the interface of the lamination of the laminated precursor 3 among the samples (it is necessary to control the parameters related to the alloying reaction such as temperature and time), The quality of the absorption layer 5 varies. Then, the In layer 32 agglomerates, and in-plane compositional nonuniformity is likely to occur.

Therefore, it has been proposed to provide a Ga concentration gradient so that the Ga concentration decreases from the interface with the Mo electrode 2 toward the surface.

However, according to the conventional method of forming the light absorption layer, Ga is Mo and Cu-In-G.
In order to segregate at the interface with the a layer, the Mo electrode 2 and CIGS
Causing a problem of poor adhesion with the light absorption layer 5 due to the thin film,
This is a cause of deterioration of battery characteristics.

Further, conventionally, it has been shown that the Na element in the soda lime glass as the substrate diffuses into the CuInSe2 film to grow grains, and the CuInS diffused with the Na element.
It has been reported that the energy conversion efficiency of a solar cell using an e2 film is enhanced (“The Influence of Sodium” by M. Bodegard et al., 12th European Photovoltaic Solar Energy Conference).
ON THE GRAIN STRUCTURE OF
CuInSe2 FILMS FOR PHOTOV
OLTAIC APPLICATIONS ").

Further, the resistance value of the CIGS film deposited on the glass containing Na component is small, and Na2 is deposited on the substrate.
In the solar cell in which the CIGS film is formed after the O2 film is deposited, the energy conversion efficiency is improved by about 2% as compared with the solar cell in which the Na2O2 film is not deposited, and the energy conversion efficiency, which largely depends on the Cu / In ratio, is Cu. It has been reported to be constant regardless of the In / In ratio {1st World Conference on Photovoltaic Energy Conversion M. "INFLUENCE OF SUBSTRATES" by Ruckh and others
ON THE ELECTRICAL PROPERT
IES OFCu (In, Gs) Se2 THINFI
LMS "}.

As can be seen from the above reports, CuInS
The diffusion or addition of Na element is effective for promoting the growth of the e2 film, increasing the carrier concentration, and improving the energy conversion efficiency of the solar cell.

As a Na doping method, there is a method of forming an alkaline layer containing an Na element on a Mo electrode (back surface electrode) by a vapor deposition method or a sputtering method, and then forming a laminated precursor and selenizing it. −
No. 222750. The problem of this manufacturing method is that, because the alkali layer formed of Na or Na compound has hygroscopicity, it deteriorates when it is exposed to the air after forming a film, resulting in peeling.

Therefore, CuInSe is formed by the vapor deposition method in which Na is doped at the same time as other elements constituting the light absorption layer.
A method of making two membranes is disclosed in US Pat. No. 542204. In addition, Cu-on the Mo electrode by the sputtering method.
A method of depositing In-O: Na2O2 is disclosed. However, in these methods, the working process is complicated.

Further, in Japanese Patent Laid-Open No. 8-222750, a barrier layer is provided between the SLG substrate and the light absorbing layer in order to prevent the diffusion of the alkali metal from the SLG substrate into the light absorbing layer. , Or using a substrate containing no alkali metal.

[0017]

The problem to be solved is to form a laminated precursor film composed of a Cu—Ga alloy layer and an In layer on the back surface electrode of a thin film solar cell made of a compound semiconductor, and in a Se atmosphere. When a CIGS-based light absorption layer is produced by heat treatment, a Na layer is formed on the back electrode by a vapor deposition method or a sputtering method in order to diffuse Na in the light absorption layer in order to improve energy conversion efficiency. Then, the deposited N
That is, the a layer is deteriorated and easily peeled off.

In addition, when the laminated precursor is selenized, Na is used.
Doping or by depositing Cu-In-O: Na2O2 on the back electrode by a sputtering method and then forming a laminated precursor film on it and selenizing it, the working process becomes complicated. There is a problem that it ends up.

In addition, SL is provided between the SLG substrate and the light absorption layer.
G A barrier layer is provided to prevent diffusion of an alkali metal from the substrate to the light absorbing layer, or a substrate containing no alkali metal is used to form an alkali metal from the alkali layer provided on the back electrode to the light absorbing layer. Diffusing (Na element) has a problem that the efficiency is low and the cost is high.

[0020]

According to the present invention, a back electrode is formed on a substrate containing an alkaline component, a precursor film is formed on the back electrode, and a heat treatment is performed in a Se atmosphere so that a CIGS system is formed. In a method for manufacturing a thin film solar cell in which a light absorbing layer is formed and a transparent electrode is formed on the light absorbing layer via a buffer layer, an alkali element is efficiently and effectively added to the light absorbing layer during the heat treatment. In order to diffuse the alkali element, the alkali element is diffused into the light absorbing layer from the alkali layer provided between the back electrode and the precursor film and the substrate.

In this case, particularly in the present invention, a diffusion control layer is formed between the substrate and the back electrode to control diffusion of the alkali element of the substrate into the light absorption layer.

Then, in the present invention, a precursor film is formed on the back surface electrode of a thin film solar cell made of a compound semiconductor, and the precursor film is heat-treated in an Se atmosphere to form a CIGS.
In order to improve the energy conversion efficiency, a layer for diffusing the alkaline component of the group Ia element in order to improve the energy conversion efficiency is obtained in a simple process when producing a light absorbing layer of a system without causing a problem of alteration or peeling. In order to enable the above, the back electrode is immersed in an aqueous solution containing an alkali metal and then dried to form an alkali layer on the back electrode.

The present invention also provides a thin-film solar cell having a structure in which a back electrode, a CIGS-based light absorption layer, a buffer layer, and a transparent electrode are sequentially laminated on a substrate containing an alkaline component, and an alcal element is added. And a diffusion control layer for controlling diffusion of the alkali element of the substrate into the light absorption layer, between the substrate and the back electrode.

[0024]

EXAMPLE As shown in FIG. 3, a thin film solar cell according to the present invention comprises a Mo electrode 2, a CIGS light absorbing layer 5 ', a buffer layer 6 and a transparent electrode 7 which are sequentially laminated on an SLG substrate 1. Of the structure, particularly N as the light absorption layer 5 '.
A diffusion control layer 8 for controlling diffusion of the Na element contained in the SLG substrate 1 to the light absorption layer 5 ′ between the SLG substrate 1 and the Mo electrode 2 while using the one to which the a element is added.
Is provided.

The diffusion control layer is made of SiO2, Al2O.
3, TiN, Si3N4, ZrO2 or TiO2.

In the present invention, the thin film solar cell having such a structure is manufactured as follows.

As a manufacturing method thereof, as shown in FIG. 4, first, the diffusion control layer 8 is formed on the SLG substrate 1 by the CVD method (step S1), and then the Mo electrode is formed on the diffusion control layer 8. 2 is formed by sputtering (step S2).

Then, an alkali layer 9 made of Na2S is formed on the Mo electrode 2 by a dipping method (step S3).

As the film formation of the alkali layer 9, for example, a film formation substrate of the Mo electrode 2 is formed by an aqueous solution of Na2S.9H2O (sodium sulfide nonahydrate) dissolved in pure water at a concentration of 0.1 to 5% by weight. After being dipped and spin-dried, a baking treatment is performed in the air at 150 ° C. for 60 minutes to adjust the residual water content in the film.

Then, as shown in FIG.
First, the In layer 41 is formed by the first sputtering process SPT-1 using the In simple substance target 1, and then the second sputtering process using the Cu-Ga alloy target T2. The Cu-Ga alloy layer 42 is formed by SPT-2, and the laminated precursor 4 including the In layer 41 and the Cu-Ga alloy layer 42 is formed. Then
In the heat treatment step HEAT, the laminated precursor 4 is heat-treated in a Se atmosphere to form a light absorption layer 5'of a CIGS thin film.

During this heat treatment, an amount of Na element optimally controlled by the diffusion control layer 8 is diffused from the SLG substrate 1 through the Mo electrode 2 to the light absorption layer 5 ′, and a predetermined amount of Na element is removed from the alkali layer 9. Diffuses in the light absorption layer 5 '.

At this time, the alkali layer 9 is formed with a predetermined amount of N in advance.
The film is formed with a film quality (content density of Na element) and film thickness capable of supplying the a element, and a predetermined amount of the Na element diffuses into the light absorption layer 5'and disappears.

Further, the film quality and film thickness of the diffusion control layer 8 are set so that even if Na element diffuses from the SLG substrate 1 into the light absorption layer 5 ', it will be in an appropriate amount without being excessively supplied. Has been done.

Specifically, 10E per 1 cm ^{2 of} unit area
The element Ma is diffused into the light absorption layer 5'with an atomic number density in the range of +10 to 10E + 16.

Further, the diffusion control layer 8 is set so that its film thickness is in the range of 100Å to 1500Å.

As described above, according to the present invention, when the laminated precursor 4 is heat-treated in the Se atmosphere, the optimally controlled amounts of Na elements from the SLG substrate 1 and the alkali layer 9 are effectively and efficiently absorbed by light. By diffusing into the layer 5 ', it becomes possible to fabricate the light absorption layer 5'of the CIGS thin film having good energy conversion efficiency.

According to the present invention, the alkali layer 9 can be easily obtained by a simple process. Further, since the film of the alkali layer 9 is formed on the Mo electrode 2 by the wet treatment, since it contains water from the beginning, there is no problem of deterioration or peeling due to moisture absorption after the film formation. Further, by using a hydrate, the water content in the film can be retained, and the water content in the film can be adjusted by the baking treatment, and the wettability is excellent.

If an aqueous solution of Na2S.9H2O is used, the concentration of the surface oxide film of the Mo electrode 2 can be effectively adjusted by adjusting the concentration to a range of 11 to 13 pH at which the surface oxide film of the Mo electrode 2 can be etched. It becomes possible to remove it, and since the S component is contained, the adhesion between the Mo electrode 2 and the light absorbing layer 5'is improved.

The advantages of forming the alkali layer 9 by the dipping method are as follows.

(1) It can be realized with a relatively simple device without requiring a large-scale device such as sputtering or vacuum deposition. Further, when a vacuum device is used, quality control of a sputtering target, a vacuum evaporation source, etc. is difficult, but since a material such as Na2S has a high hygroscopic property, it is easy to control the humidity of the material by the dipping method.

(2) Even on the surface of a substrate or an electrode having a texture structure for confining light, it is possible to form the alkali layer 9 which is well adapted to the surface.
Further, as a place where the aqueous solution of Na2S.9H2O is dipped, it is formed on the surface of the laminated precursor 4, the surface of the light absorption layer 5'after selenization, and the light absorption layer 5 ', in addition to the surface of the Mo electrode 2. The surface of the buffer layer 6 may be considered, but good coverage can be secured at the molecular level even on a surface having extremely large roughness such as the surface of the laminated precursor 4 or the surface of the light absorption layer 5 '.

When dipping the surface of the Mo electrode 2, an aqueous solution of an alkali metal is used.
The effect of etching the surface oxide film and the effect of removing particles can be obtained. This makes it possible to omit the surface cleaning step after the laser scraping of the Mo electrode 2. Further, in order to more effectively clean the surface of the Mo electrode 2, it is possible to add ammonia, NaOH or the like to the solution.
H can be easily adjusted.

Since the solution is dipped in the aqueous solution, oxygen and hydrogen remain in the alkali layer 9, and the oxygen is taken into the light absorption layer 5 ', so that the semiconductor characteristics are improved.

The results of finding the amount of Na element deposited when the alkali layer 9 is formed on the Mo electrode 2 by the dipping method are as follows.

6 ml of ultrapure water was added dropwise to the film-forming portion by ICP-MS analysis using two samples diluted with 1% Y2Y-51 Na2S 0.2% and 1Y16-52 Na2S 0.8%. Then, Na was collected while scanning with the liquid transfer tool for about 5 minutes. As a result, the former sample was 2.8E + 15 (atoms / c) per unit area.
m ² ), and the latter sample had an atom number of 8.7E + 15 (atoms / cm ² ) per unit area. The limit of quantification is about 2E + 10.

FIG. 6 shows the energy conversion efficiency η when the light absorbing layer 5'is manufactured by changing the concentration of the Na2S aqueous solution.
It is a characteristic view which shows the measurement result of [%] S = 0.16. The measurement range when using a plurality of samples is w1, w2, w3
It is represented by ...

According to this measurement result, the concentration of the Na2S aqueous solution is 0.01 in terms of energy conversion efficiency η.
The range of 1.0 (5) is appropriate. In that case, Na2
When the concentration of the S aqueous solution is low, the energy conversion efficiency η is low, and when the concentration is high, peeling due to etching occurs between the Mo electrode 2 and the SLG substrate 1.

FIG. 7 shows a Na2S aqueous solution (concentration 0.27).
(%) Is a characteristic diagram showing measurement results of energy conversion efficiency η [%] S = 0.16 when the light absorption layer 5 ′ is manufactured by changing the liquid temperature.

According to the measurement results, the liquid temperature of the Na2S aqueous solution is 10 ° C at room temperature in terms of energy conversion efficiency η.
The range of ℃ ~ 70 ℃ is appropriate (preferably 15 ℃ ~ 4
0 ° C range). In that case, if the liquid temperature of the Na2S aqueous solution is low, the energy conversion efficiency η deteriorates, and if it is 80 ° C or higher, M
Stripping due to etching occurs between the o electrode 2 and the SLG substrate 1.

FIG. 8 shows the energy conversion efficiency η [%] S = when the light absorption layer 5'is produced by changing the baking temperature when the alkali layer 9 is baked (processing time 60 minutes).
It is a characteristic view which shows the measurement result of 0.16.

According to this measurement result, the baking temperature is 100 ° C. to 400 ° C. in terms of energy conversion efficiency η.
Is appropriate (preferably in the range of 100 ° C to 250 ° C). In that case, if the baking temperature is low, the energy conversion efficiency η is deteriorated, and if the baking temperature is high, the water content of the alkali layer 9 is decreased, and the peeling is likely to occur.

FIG. 9 shows the energy conversion efficiency η [%] S = 0.1 when the light absorption layer 5'is manufactured by changing the baking time when the alkali layer 9 is baked at a temperature of 150 ° C.
It is a characteristic view which shows the measurement result of No. 6.

According to this measurement result, the baking time is 10 to 10 in terms of energy conversion efficiency η and workability.
A range of 60 minutes is appropriate.

In the present invention, an aqueous solution containing a Group Ia element used for forming the alkali layer 9 by the dipping method is used.
In addition to using a2S.9H2O hydrate, it is possible to use an aqueous solution of other alkali metal or its sulfide, hydroxide, chloride and the like.

Specifically, the following aqueous solutions are used. Na compound: Na2SeO3.5H2O, Na2TeO
3.5H2O, Na2SO3 / 7H2O, Na2B4O
7 ・ 10H2O, AlNa (SO4) 2 ・ 12H2O,
NaCl K compound: K2TeO3 · 3H2O, K2A12O4 ·
3H2O, AlK (SO4) 2.12H2O, KOH,
KFLi

Further, in the present invention, since the In layer 41 is provided on the Mo electrode 2 and then the Cu—Ga alloy layer 42 is provided thereon to form the laminated precursor 4, the Mo electrode 2 is formed. It is possible to suppress alloying due to solid layer diffusion of elements at the interface with. Then, when the laminated precursor 4 is heat-treated in a Se atmosphere to be selenized, the In component can be sufficiently diffused to the Mo electrode 2 side, and Ga having a slow diffusion rate is formed at the interface with the Mo electrode 2. A CIG made of Cu (In + Ga) Se2, which is a high-quality P-type semiconductor with a uniform crystal, is formed so that a Cu-Ga-Se layer having poor crystallinity is not formed by segregation.
The light absorption layer 5'of S can be produced.

Therefore, a different layer (Cu-Ga-Se layer) having poor crystallinity and structurally fragility and conductivity is interposed between the Mo electrode 2 and the light absorption layer 5 '. Therefore, it becomes possible to obtain a solar cell having high adhesion to the Mo electrode 2 and being structurally strong and having good cell characteristics.

Further, in the present invention, as shown in FIG.
After forming the alkali layer 9 made of Na2S on the Mo electrode 2, Cu-G is formed on the Alcal layer 9 here.
The laminated precursor 4'having a structure in which the a-alloy layer 42 is sandwiched between the In layers 41 and 43 is formed by sputtering.

Thus, according to the present invention, the Mo electrode 2
Since the In layer 41 is provided on the Cu layer and the Cu—Ga alloy layer 42 is provided on the In layer 41, alloying due to solid layer diffusion of elements at the interface with the Mo electrode 2 can be suppressed. When the laminated precursor 4 is heat-treated in a Se atmosphere to be selenized, the In component can be sufficiently diffused to the Mo electrode 2 side, and Ga having a slow diffusion rate segregates at the interface with the Mo electrode 2. As a result, a Cu-Ga-Se layer having poor crystallinity is not formed. Further, since the surface is covered with the In layer 43, Cu2 is formed on the surface of the light absorption layer 5'produced by selenization.
Se will not be generated.

Therefore, a different layer (Cu-Ga-Se) having poor crystallinity and being structurally fragile and having conductivity may be interposed between the Mo electrode 2 and the light absorption layer 5 '. And a high-quality P-type semiconductor Cu (In + Ga) Se2 as a CIGS light-absorbing layer with a uniform crystal that does not form a conductive different layer (Cu2Se) on the surface of the light-absorbing layer 5 '. 5'can be made, M
It is possible to obtain a solar cell having high adhesion to the o electrode 2 and being structurally strong, and having good cell characteristics without leakage.

Further, according to the present invention, as shown in FIG.
On the o electrode 2, a plurality of structures in which a Cu—Ga alloy layer is sandwiched by In layers are provided in multiple stages to form a laminated precursor 4 ″.

Here, on the Mo electrode 2, the In layer 41,
The Cu—Ga alloy layer 42, the In layer 43, the Cu—Ga alloy layer 44, the In layer 45, the Cu—Ga alloy layer 46, and the In layer 47 were sequentially laminated, so that the Cu—Ga alloy layer was sandwiched between the In layers. The structure is provided in three stages.

Thus, the In layer 41 is formed on the Mo electrode 2 side.
However, since the In layer 47 is arranged on the surface and the Cu—Ga alloy layer 42, the In layer 43, the Cu—Ga alloy layer 44, the In layer 45 and the Cu—Ga alloy layer 46 are evenly distributed between them, C of high quality P-type semiconductor with more uniform crystal
CIGS light absorption layer 5'of u (In + Ga) Se2
Will be able to be manufactured.

FIG. 12 shows another method for producing the light absorption layer 5 '.

Here, when forming the light absorption layer 5'in a thin film solar cell made of a compound semiconductor, a group Ib group metal element and a group IIIb group metal element are simultaneously supplied to form a precursor alloy film of a single layer. Then, the formed precursor film is heat-treated in a Se atmosphere to be selenized.

Specifically, M formed on the SLG substrate 1
When forming the light absorption layer 5 ′ of the CIGS thin film on the o electrode 2, the sputtered particles of each target material are formed on the alkali layer 9 by the facing target type sputtering in which the In target T 1 and the Cu—Ga alloy target T 2 are provided. Sputter process FT-SPT for forming a single-layer precursor film 10 made of a Cu-Ga-In alloy in a mixed state, and the precursor film 10 is heat-treated in an Se atmosphere to form a light absorption layer of a CIGS thin film. The heat treatment step HEAT for forming No. 5 is performed.

FIG. 13 shows a case where the precursor film 10 of Cu—Ga—In alloy is formed by the facing target type sputtering in a state where the sputtered particles in the In target T1 and the Cu—Ga alloy target T2 are mixed. The state of the sputtered particles is shown.

When the In target T1 and the 2Cu—Ga alloy target T2 provided in a pair are simultaneously sputtered, the particles sputtered from one target reach the surface of the other target. As a result, the metal elements Cu, Ga, and In from both target materials are mixed on the surface of each target, and further sputtering is performed in this state, and the sputtered particles in which both target materials are mixed are A Cu—Ga—In alloy precursor film 10 is formed by depositing and depositing on the alkali layer 9 of the material.

At this time, a part of the In particles and Cu-Ga particles sputtered from each target T1 and T2 jumps directly toward the base material without reaching the surface of the other target, but the jumping angle of the sputtered particles is increased. From the above probability, the adhesion of unmixed Cu—Ga particles and In particles is extremely small, and the adhesion of the mixed sputtered particles to the substrate becomes dominant.

According to this method, it is not a precursor in which an In layer and a Cu—Ga layer are laminated, but a single particle in which In particles and Cu—Ga particles sputtered from the targets T1 and T2 are mixed from the beginning. Layer precursor film 10
Therefore, the metal elements of Cu, Ga, and In are evenly distributed in the thin film as compared with the case of the laminated precursor, and the promotion of alloying due to the solid layer diffusion between the metal elements can be suppressed. Like Further, it becomes possible to evenly selenize the precursor film 10 in the heat treatment process performed later.

As a result, it is also effective in suppressing a different phase (a crystal phase different from the crystal structure originally intended to be produced) which causes deterioration in performance of the thin film solar cell made of a compound semiconductor. In addition, the fact that the layer on which the metal precursor 3 is formed has an amorphous pseudo structure is another factor that makes it possible to obtain a light absorption layer 5'of a high quality CIGS thin film.

Further, since the precursor film 10 to be formed has a ternary alloy deposition structure, a short circuit as a battery is unlikely to occur.

Further, the simultaneous sputtering of the targets T1 and T2 enables the precursor film 10 to be formed at high speed.

Then, the single-layer precursor film 1 in which the metal elements of Cu, Ga, In are uniformly distributed in the thin film as described above.
0 is heat-treated in a Se atmosphere to be selenized to obtain a high-quality CIG of Cu (In + Ga) Se2.
It becomes possible to form the light absorption layer (p-type semiconductor) 5'of the S thin film.

It has been confirmed that the photoelectric conversion efficiency of the light absorption layer 5'formed by selenizing the precursor film 10 is 15% or more.

FIG. 14 shows H2Se gas (Ar of 5% concentration).
By the heat treatment using (gas dilution), a thermochemical reaction (gaseous Se conversion) is caused to produce a characteristic of the temperature in the furnace when the light absorption layer 5'of the CIGS thin film is formed from the precursor film 10 (the laminated precursor 4). An example is shown.

Here, when the temperature in the furnace reaches 100 ° C. after the heating is started, preheating is performed for 10 minutes to stabilize the furnace. Then, the temperature in the furnace is raised to 500 to 520 ° C. over 30 minutes so that the SLG substrate 1 does not warp and a high quality crystal can be obtained by high heat treatment, as a time period during which stable lamp-up is possible. At that time, the supply of Se by thermal decomposition of H2Se gas is started from the time t1 when the temperature in the furnace reaches 230 to 250 ° C.
Then, in order to obtain high quality crystals by high heat treatment, heat treatment is performed for 40 minutes while keeping the furnace temperature at 500 to 520 ° C.

At that time, the temperature in the furnace was 1 after the heating was started.
From the time when the temperature reached 00 ° C., H 2 Se gas was charged at a low temperature, and heat treatment was performed while maintaining a constant pressure in the furnace. Then, at the time t2 when the heat treatment is completed, the inside of the furnace is replaced with Ar gas at a low pressure of about 100 Pa in order to prevent unnecessary precipitation of Se.

When forming the precursor film 10 by the facing target type sputtering, the pair of target materials is not limited to the combination of Cu—Ga alloy and In, but other Cu—Ga alloy or Cu—Al alloy and In may be used. A combination of -Cu alloy, a combination of Cu and In or Al, and a combination of Cu and In-Cu alloy are possible.
Basically, an alloy of Group Ib metal-Group IIIb metal, Ib
Two kinds of group metals and group IIIb metals may be used in combination.

[0080]

As described above, according to the present invention, the back electrode is formed on the substrate containing the alkaline component, the precursor film is formed on the back electrode, and the heat treatment is performed in the Se atmosphere.
When manufacturing a thin film solar cell in which a GS-based light absorbing layer is formed and a transparent electrode is formed on the light absorbing layer via a buffer layer, an alkali provided between the back electrode and the precursor film is used. Since the alkali element is diffused into the light absorption layer from the layer and the substrate respectively, the alkali element can be efficiently and effectively diffused into the light absorption layer during the heat treatment.

At this time, according to the present invention, since the diffusion control layer is formed between the substrate and the back surface electrode, the alkali element of the substrate is not excessively supplied, and the alkali is added to the light absorption layer. The element can be diffused properly.

Then, according to the present invention, a precursor film is formed on the back surface electrode of a thin film solar cell made of a compound semiconductor, and heat treatment is performed in a Se atmosphere to obtain CI.
When the GS-based light absorbing layer is produced, the back electrode is immersed in an aqueous solution containing an alkali metal and then dried to form an alkali layer on the back electrode. It becomes possible to obtain a layer for diffusing the alkali component of the group Ia element in the absorption layer by a simple process without causing the problem of alteration or peeling.

Further, the present invention relates to a thin film solar cell having a structure in which a back electrode, a CIGS light absorbing layer, a buffer layer and a transparent electrode are sequentially laminated on a substrate containing an alkali component, and an alkali element is added. In addition to the above described light absorption layer, a diffusion control layer for controlling the diffusion of the alkali element of the substrate into the light absorption layer is provided between the substrate and the back electrode so that the alkali element is properly diffused. The light absorption layer has an advantage that the energy conversion efficiency can be effectively improved.

[Brief description of drawings]

FIG. 1 is a front cross-sectional view showing the basic structure of a thin film solar cell using a general compound semiconductor.

FIG. 2 is a diagram showing a conventional process for producing a light absorption layer on a back electrode.

FIG. 3 is a front sectional view showing an example of the structure of a thin-film solar cell according to the present invention.

FIG. 4 is a diagram showing a process of sequentially forming a diffusion control layer, a back electrode and an alkali layer on an SLG substrate according to the present invention.

FIG. 5 is a diagram showing a process of forming a laminated precursor on an alkali layer to produce a light absorption layer according to the present invention.

FIG. 6 is a characteristic diagram showing a measurement result of energy conversion efficiency when a light absorbing layer is manufactured by changing the concentration of a Na2S aqueous solution.

FIG. 7 is a characteristic diagram showing measurement results of energy conversion efficiency when a light absorbing layer is produced by changing the liquid temperature of a Na2S aqueous solution.

FIG. 8 is a characteristic diagram showing measurement results of energy conversion efficiency when a light absorbing layer is produced by changing the temperature when baking the alkali layer.

FIG. 9 is a characteristic diagram showing measurement results of energy conversion efficiency when a light absorbing layer is produced by changing the time of baking an alkali layer.

FIG. 10 is a front sectional view showing a laminated precursor having a structure in which a Cu—Ga alloy layer is sandwiched between In layers on an alkali layer.

FIG. 11 is a front sectional view showing a structure of a laminated precursor when a structure in which a Cu—Ga alloy layer is sandwiched between In layers is provided on an alkali layer in multiple stages.

FIG. 12 is a diagram showing a process for producing a light absorbing layer by forming a precursor film of a single layer on an alkali layer according to the present invention.

FIG. 13 is a diagram showing a state of sputtered particles when a single-layer precursor film is formed by facing target type sputtering.

FIG. 14 is a diagram showing an example of heating characteristics when a precursor film is heat-treated in a Se atmosphere to form a CIGS thin film according to the present invention.

[Explanation of symbols]

1 SLG substrate 2 Mo electrode 4 laminated precursor 5'light absorbing layer 6 buffer layers 7 Transparent electrode 8 Diffusion control layer 9 Alkaline layer

Claims (12)

[Claims] 1. A back electrode is formed on a substrate containing an alkaline component, and a precursor film is formed on the back electrode, and S
In a method for manufacturing a thin-film solar cell, a CIGS-based light absorption layer is produced by heat treatment in an e atmosphere, and a transparent electrode is formed on the light absorption layer via a buffer layer. An alkali layer is formed between the precursor film and the precursor film, and heat treatment is performed in a Se atmosphere to obtain CI.
A method of manufacturing a thin-film solar cell, wherein an alkali element is diffused from the substrate and the alkali layer into the light absorption layer when the GS-based light absorption layer is manufactured. 2. The method for producing a thin film solar cell according to claim 1, wherein the back electrode is immersed in an aqueous solution containing a Group Ia element and then dried to form an alkali layer on the back electrode. . 3. The method for producing a thin film solar cell according to claim 2, which is an aqueous solution in which a hydrate of a compound containing a Group Ia element is dissolved. 4. The method for manufacturing a thin film solar cell according to claim 2, wherein the Group Ia element is Na and the alkali layer is Na 2 S or Na 2 Se. 5. A diffusion control layer is formed between the substrate and the back electrode to control diffusion of an alkali element of the substrate into the light absorption layer. Method for manufacturing thin film solar cell. 6. A diffusion control layer comprising SiO2, Al2O3, T
The method for manufacturing a thin film solar cell according to claim 5, wherein the thin film solar cell is formed of iN, Si3N4, ZrO2 or TiO2. 7. The film thickness of the diffusion control layer is 100Å to 1500.
The method for producing a thin film solar cell according to claim 5, wherein the range is set to Å. 8. The concentration of the alkali element diffused in the light absorption layer is 10E + 10 to 10E + 16 per unit area 1 cm ^2.
The method for manufacturing a thin-film solar cell according to claim 1, wherein the number of atoms is within the range. 9. A thin film solar cell having a structure in which a back electrode, a CIGS light absorbing layer, a buffer layer and a transparent electrode are sequentially laminated on a substrate containing an alkaline component, wherein the light absorbing material contains an alcal element. A thin-film solar cell comprising a layer and a diffusion control layer for controlling diffusion of an alkali element of the substrate into the light absorption layer between the substrate and the back electrode. 10. 10E + 10 per unit area 1 cm ²
The thin film solar cell according to claim 9, wherein a concentration of an alkali element in the range of 10E + 16 atoms is added to the light absorption layer. 11. The diffusion control layer comprises SiO2, Al2O3,
The thin film solar cell according to claim 9, wherein the thin film solar cell comprises TiN, Si3N4, ZrO2 or TiO2. 12. The thin film solar cell according to claim 9, further comprising a diffusion control layer having a film thickness in the range of 100Å to 1500Å.