JP4110515B2 - Thin film solar cell and manufacturing method thereof - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a thin film solar cell using a compound semiconductor and a method for producing the same.
[0002]
[Prior art]
FIG. 1 shows a basic structure of a thin film solar cell made of a general chalcopyrite compound semiconductor. The Mo electrode 2 to be a back electrode (plus electrode) is formed on the SLG (soda lime glass) substrate 1, the light absorption layer 5 is formed on the Mo electrode 2, and ZnS, A transparent electrode 7 made of ZnO: Al or the like serving as a negative electrode is formed through a buffer layer 6 made of CdS or the like.
[0003]
As the light absorption layer 4 in the thin film solar cell using the compound semiconductor, an Ib-IIIb-VIb2 group based on Cu, (In, Ga), Se is used as a material having a high energy conversion efficiency exceeding 18%. A CIGS thin film of Cu (In + Ga) Se2 is used.
[0004]
Conventionally, as a method of producing a light absorption layer using a CIGS thin film, there is a selenization method in which a Se compound is generated by a thermochemical reaction using a Se source such as H 2 Se gas using a metal precursor (precursor) thin film.
[0005]
In U.S. Pat. No. 4,798,660, a metal thin film layer formed by DC magnetron sputtering in the order of a back electrode → a pure Cu single layer → a pure In single layer is formed in a Se atmosphere, preferably H2Se gas. Forming a light absorption layer composed of a CIS single phase having a uniform composition.
[0006]
In JP-A-10-135495, as a metal precursor, a metal thin film formed by sputtering using a Cu—Ga alloy target and a metal thin film formed by sputtering using an In target are used. Things are shown.
[0007]
As shown in FIG. 2, when forming the light absorption layer 5 by the CIGS thin film on the Mo electrode 2 formed on the SLG (soda lime glass) substrate 1, the Cu—Ga alloy target T2 is first formed. The Cu—Ga alloy layer 31 is formed by the first sputtering step SPT-1 used, and then the In layer 32 is formed by the second sputtering step SPT-2 using the In target T1, and Cu— A laminated precursor 3 composed of a Ga alloy layer 31 and an In layer 32 is formed. Then, in the heat treatment step HEAT, the laminated precursor 3 is heat-treated in a Se atmosphere, so that the light absorption layer 5 made of a CIGS thin film is produced.
[0008]
However, when the precursor 3 having a stacked structure of the Cu—Ga alloy layer 31 and the In layer 32 is formed, alloying is performed by solid layer diffusion (diffusion between solids) at the interface of the stacked layer during film formation or stocking. The reaction proceeds to form a Cu—In—Ga ternary alloy. Further, the alloying reaction proceeds also in the Se conversion step performed later. It is difficult to uniformly control the progress of the alloying reaction at the interface between the layers of the stacked precursor 3 between samples (it is necessary to manage parameters related to the alloying reaction such as temperature and time), and the light obtained The quality of the absorption layer 5 will vary. Then, the In layer 32 aggregates, and compositional inhomogeneity tends to occur in the surface.
[0009]
For this reason, 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.
[0010]
However, according to such a conventional method for forming a light absorption layer, since Ga segregates at the interface between the Mo electrode 2 and the Cu—In—Ga layer, the light absorption layer 5 composed of the Mo electrode 2 and the CIGS thin film This causes the problem of poor adhesion and causes deterioration of battery characteristics.
[0011]
Conventionally, it has been shown that Na element in soda lime glass serving as a substrate diffuses into the CuInSe2 film and grows grains, and the energy conversion efficiency of the solar cell using the CuInSe2 film in which the Na element diffuses increases. (The 12th European Photovoltaic Solar Energy Conference "THE INFLUENCE OF SODIUM ON THE GRAIN STRUCTURE OF CuInSe2 FILMS FOR PHOTOVOLTAIC APPLICATIONS" by M. Bodegard et al.).
[0012]
Furthermore, the resistance value of the CIGS film deposited on the glass containing the Na component is small, and in the solar cell in which the CIGS film is formed after depositing the Na2O2 film on the substrate, the energy conversion efficiency does not deposit the Na2O2 film. It has been reported that the energy conversion efficiency, which is about 2% higher than that of solar cells, and which is usually highly dependent on the Cu / In ratio, is constant regardless of the Cu / In ratio. {1st Photovoltaic Energy Conversion World Conference M.M. "INFRUENCE OF SUBSTRATES ON THE ELECTRICAL PROPERITES OF Cu (In, Gs) Se2 THINFILMS"} by Ruckh et al.}.
[0013]
As can be seen from the above reports, the diffusion or addition of Na element is effective for promoting the growth of the CuInSe2 film, increasing the carrier concentration, and improving the energy conversion efficiency of the solar cell.
[0014]
As a method for doping Na, Japanese Patent Application Laid-Open No. 8-222750 discloses a method in which an alkali layer containing an Na element is formed on a Mo electrode (back electrode) by vapor deposition or sputtering, and then a laminated precursor is formed and selenized. Shown in the specification. The problem with this manufacturing method is that the alkali layer made of Na or Na compound has a hygroscopic property, so that it changes in quality when it is exposed to the atmosphere after film formation, resulting in peeling.
[0015]
Therefore, US Pat. No. 542204 discloses a method for producing a CuInSe2 film by a vapor deposition method in which Na is doped simultaneously with other elements constituting the light absorption layer. In addition, a method of depositing Cu—In—O: Na 2 O 2 on a Mo electrode by a sputtering method is disclosed. However, in these methods, the work process is complicated.
[0016]
Japanese Patent Application Laid-Open No. 8-222750 discloses that a barrier layer is provided between the SLG substrate and the light absorption layer in order to prevent the alkali metal from diffusing from the SLG substrate to the light absorption layer. The use of a substrate containing no metal is disclosed.
[0017]
[Problems to be solved by the invention]
The problem to be solved is that a CIGS-based light absorption is achieved by forming a laminated precursor film composed of a Cu—Ga alloy layer and an In layer on a back electrode in a thin film solar cell using a compound semiconductor and heat-treating it in an Se atmosphere. In forming the layer, in order to diffuse Na into the light absorption layer in order to improve energy conversion efficiency, the Na layer is formed on the back electrode by vapor deposition or sputtering. It becomes a thing which changes in quality and is easy to peel.
[0018]
In addition, when the laminated precursor is selenized, Na is doped, or Cu—In—O: Na 2 O 2 is deposited on the back electrode by a sputtering method, and then a laminated precursor film is formed thereon and selenized. There is a problem that the work process becomes complicated.
[0019]
Further, a barrier layer for preventing diffusion of alkali metal from the SLG substrate to the light absorption layer is provided between the SLG substrate and the light absorption layer, or a substrate that does not contain alkali metal is used on the back electrode. If the alkali metal (Na element) is diffused from the provided alkali layer to the light absorption layer, there is a problem that the efficiency is low and the cost is increased.
[0020]
[Means for Solving the Problems]
The present invention forms a CIGS-based light absorption layer by forming a back electrode on a substrate containing an alkali component, forming a precursor film on the back electrode, and performing heat treatment in an Se atmosphere. In a method for manufacturing a thin-film solar cell in which a transparent electrode is formed on an absorption layer via a buffer layer, an alkali element can be efficiently and effectively diffused into the light absorption layer during the heat treatment. Accordingly, an alkali element is diffused into the light absorption layer from the alkali layer and the substrate provided between the back electrode and the precursor film.
[0021]
At that time, in the present invention, in particular, a diffusion control layer is formed between the substrate and the back electrode to control the diffusion of the alkali element of the substrate into the light absorption layer.
[0022]
In the present invention, when a CIGS-based light absorption layer is formed by forming a precursor film on the back electrode of a thin film solar cell using a compound semiconductor and performing heat treatment in an Se atmosphere, the energy conversion efficiency is improved. The back electrode is immersed in an aqueous solution containing an alkali metal so that a layer for diffusing the alkali component of the group Ia element in the light absorption layer can be obtained in a simple process without causing deterioration or peeling. After that, it is dried to form an alkali layer on the back electrode.
[0023]
The present invention also relates to 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 alkali component, and the light to which an alkane element is added. In addition to providing an absorption layer, a diffusion control layer is provided between the substrate and the back electrode to control diffusion of alkali elements of the substrate into the light absorption layer.
[0024]
【Example】
The thin film solar cell according to the present invention has a structure in which a Mo electrode 2, a CIGS light absorption layer 5 ', a buffer layer 6 and a transparent electrode 7 are sequentially laminated on an SLG substrate 1 as shown in FIG. In particular, the light absorbing layer 5 ′ is used with the addition of Na element, and the Na element contained in the SLG substrate 1 is diffused between the SLG substrate 1 and the Mo electrode 2 into the light absorbing layer 5 ′. A diffusion control layer 8 for controlling the above is provided.
[0025]
The diffusion control layer is made of SiO2, Al2O3, TiN, Si3N4, ZrO2 or TiO2.
[0026]
In the present invention, a thin-film solar cell having such a structure is manufactured as follows.
[0027]
As a manufacturing method thereof, as shown in FIG. 4, first, a diffusion control layer 8 is formed on the SLG substrate 1 by a CVD method (step S1), and then a Mo electrode 2 is sputtered on the diffusion control layer 8. (Step S2).
[0028]
Next, an alkali layer 9 made of Na2S is formed on the Mo electrode 2 by dipping (step S3).
[0029]
As the film formation of the alkali layer 9, for example, the film formation substrate of the Mo electrode 2 is immersed in an aqueous solution in which Na 2 S · 9H 2 O (sodium sulfide nonahydrate) is dissolved in pure water at a weight concentration of 0.1 to 5%. After spin-drying, a baking process is performed in the atmosphere at 150 ° C. for 60 minutes in order to adjust the residual moisture in the film.
[0030]
Then, as shown in FIG. 5, the In layer 41 is first formed on the alkali layer 9 by the first sputtering step SPT- 1 using the In simple substance target 1, and then Cu—Ga is formed thereon. The Cu—Ga alloy layer 42 is formed by the second sputtering step SPT-2 using the alloy target T2 to form the laminated precursor 4 including the In layer 41 and the Cu—Ga alloy layer 42. Next, in the heat treatment step HEAT, the laminated precursor 4 is heat-treated in a Se atmosphere to produce a light absorption layer 5 ′ using a CIGS thin film.
[0031]
During this heat treatment, an amount of Na element optimally controlled by the diffusion control layer 8 from the SLG substrate 1 diffuses into the light absorption layer 5 ′ through the Mo electrode 2 and a predetermined amount of Na element from the alkali layer 9 Diffuses 5 '.
[0032]
At that time, the alkali layer 9 is formed in advance with a film quality (content density of Na element) and a film thickness capable of supplying a predetermined amount of Na element, and the predetermined amount of Na element diffuses into the light absorption layer 5 ′. Disappear.
[0033]
Further, the film quality and film thickness of the diffusion control layer 8 are set so that the Na element diffused from the SLG substrate 1 to the light absorption layer 5 ′ is appropriately supplied without being excessively supplied. .
[0034]
Specifically, unit area 1cm ² The Ma element is diffused into the light absorption layer 5 ′ with an atomic number density in the range of 10E + 10 to 10E + 16 per unit.
[0035]
Further, the diffusion control layer 8 is set so that its film thickness is in the range of 100 to 1500 mm.
[0036]
As described above, according to the present invention, when the laminated precursor 4 is heat-treated in the Se atmosphere, the optimally controlled amount of Na element from the SLG substrate 1 and the alkali layer 9 can be effectively and efficiently applied to the light absorbing layer 5 ′. Thus, the light absorption layer 5 ′ made of CIGS thin film with good energy conversion efficiency can be produced.
[0037]
And according to this invention, the alkali layer 9 can be obtained easily with a simple process. Further, since the film of the alkali layer 9 is formed on the Mo electrode 2 by wet treatment, since moisture is contained from the beginning, there is no problem of quality change or peeling due to moisture absorption after film formation. Further, by using a hydrate, the moisture in the film can be retained, the moisture in the film can be adjusted by baking, and the wettability is excellent.
[0038]
Moreover, if the aqueous solution of Na2S · 9H2O is used, the surface oxide film on the Mo electrode 2 can be effectively removed by adjusting the concentration thereof to a range of about 11 to 13 pH at which the surface oxide film on the Mo electrode 2 can be etched. In addition, since the S component is contained, the adhesion between the Mo electrode 2 and the light absorption layer 5 'is improved.
[0039]
Advantages of forming the alkali layer 9 by the dipping method are as follows.
[0040]
(1) A large-scale apparatus such as sputtering or vacuum deposition is not required, and it can be realized with a relatively simple apparatus. In addition, when a vacuum apparatus is used, quality control of a sputtering target, a vacuum evaporation source, or the like is difficult, but a material such as Na2S has high hygroscopicity, so that the humidity of the material can be easily managed by the dipping method.
[0041]
(2) Even on a substrate or electrode surface having a texture structure for confining light, it is possible to form an alkali layer 9 that is well adapted to the surface. In addition to the surface of the Mo electrode 2, the location where the aqueous solution of Na 2 S · 9H 2 O is immersed 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 ′. The surface of the buffer layer 6 can be considered, but even a surface with extremely large roughness such as the surface of the laminated precursor 4 and the surface of the light absorption layer 5 ′ can ensure good coverage at the molecular level.
[0042]
In the case of immersing the surface of the Mo electrode 2, an etching effect and a particle removing effect of the surface oxide film of the Mo electrode 2 can be obtained by using an alkali metal aqueous solution. Thereby, it becomes possible to omit the surface cleaning process after laser scribing of the Mo electrode 2. Moreover, in order to perform the surface cleaning of the Mo electrode 2 more effectively, the pH can be easily adjusted by adding ammonia, NaOH or the like to the solution.
[0043]
Due to the immersion of the aqueous solution, oxygen and hydrogen remain in the alkali layer 9, and the oxygen is taken into the light absorption layer 5 ', thereby improving the semiconductor characteristics.
[0044]
The knowledge result of the precipitation amount of Na element when the alkali layer 9 is formed on the Mo electrode 2 by the dipping method is as follows.
[0045]
Using two samples diluted with 1Y16-51 Na2S 0.2% and 1Y16-52 Na2S 0.8%, respectively, 6 ml of ultrapure water was dropped on the film-forming portion by ICP-MS analysis. Na was collected while scanning with a transfer tool for 5 minutes. As a result, in the former sample, 2.8E + 15 (atoms / cm per unit area) ² ), And in the latter sample, 8,7E + 15 (atoms / cm per unit area) ² ) Number of atoms was obtained. The limit of quantification is about 2E + 10.
[0046]
FIG. 6 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 concentration of the Na 2 S aqueous solution. The measurement range when using a plurality of samples is represented by w1, w2, w3,.
[0047]
According to this measurement result, the concentration of the Na 2 S aqueous solution is appropriately in the range of 0.01 to 1.0 (5) in terms of energy conversion efficiency η. In that case, if the concentration of the Na 2 S aqueous solution is low, the energy conversion efficiency η is deteriorated, and if it is high, peeling by etching occurs between the Mo electrode 2 and the SLG substrate 1.
[0048]
FIG. 7 is a characteristic diagram showing a measurement result of energy conversion efficiency η [%] S = 0.16 when the light absorption layer 5 ′ is produced by changing the liquid temperature of the Na 2 S aqueous solution (concentration 0.27%). .
[0049]
According to this measurement result, the liquid temperature of the Na 2 S aqueous solution is appropriately in the range of 10 ° C. to 70 ° C. at room temperature (preferably in the range of 15 ° C. to 40 ° C.) in terms of energy conversion efficiency η. In that case, if the liquid temperature of the Na 2 S aqueous solution is low, the energy conversion efficiency η is deteriorated, and if it is 80 ° C. or higher, peeling by etching occurs between the Mo electrode 2 and the SLG substrate 1.
[0050]
FIG. 8 shows the measurement results of energy conversion efficiency η [%] S = 0.16 when the light absorption layer 5 ′ was produced by changing the baking temperature when baking the alkali layer 9 (processing time 60 minutes). FIG.
[0051]
According to this measurement result, the baking temperature is suitably in the range of 100 ° C. to 400 ° C. (preferably in the range of 100 ° C. to 250 ° C.) in terms of energy conversion efficiency η. In that case, when the baking temperature is low, the energy conversion efficiency η is deteriorated, and when the baking temperature is high, the moisture content of the alkali layer 9 is reduced, and the peeling easily occurs.
[0052]
FIG. 9 shows the measurement results of energy conversion efficiency η [%] S = 0.16 when the light absorption layer 5 ′ is produced by changing the baking time when baking the alkali layer 9 at a temperature of 150 ° C. FIG.
[0053]
According to this measurement result, the baking time is appropriately in the range of 10 to 60 minutes from the viewpoint of energy conversion efficiency η and workability.
[0054]
The present invention is not limited to using Na2S.9H2O hydrate as an aqueous solution containing a group Ia element used for forming the alkali layer 9 by the dipping method, but also other alkali metals or sulfides, hydroxides, chlorides thereof. It is possible to use an aqueous solution such as
[0055]
Specifically, the following aqueous solutions are used.
Na compound: Na2SeO3 · 5H2O, Na2TeO3 · 5H2O, Na2SO3 · 7H2O, Na2B4O7 · 10H2O, AlNa (SO4) 2 · 12H2O, NaCl
K compound: K2TeO3 · 3H2O, K2A12O4 · 3H2O, AlK (SO4) 2 · 12H2O, KOH, KF
Li
[0056]
In the present invention, since the In layer 41 is provided on the Mo electrode 2 and the Cu—Ga alloy layer 42 is provided thereon to form the laminated precursor 4, the interface with the Mo electrode 2 is provided. Alloying due to solid layer diffusion of elements in 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 low diffusion rate is formed at the interface with the Mo electrode 2. A CIGS light-absorbing layer 5 ′ made of Cu (In + Ga) Se2 of high-quality P-type semiconductor by uniform crystal is produced so as not to segregate and form a Cu—Ga—Se layer having poor crystallinity. can do.
[0057]
Therefore, a different layer (Cu—Ga—Se layer) having poor crystallinity and structurally brittle and conductive is not interposed between the Mo electrode 2 and the light absorption layer 5 ′. A solar cell having high adhesion to the Mo electrode 2, structurally strong, and good battery characteristics can be obtained.
[0058]
Further, in the present invention, as shown in FIG. 10, an alkali layer 9 made of Na 2 S is formed on the Mo electrode 2, and here, a Cu—Ga alloy layer 42 is formed on the Alkal layer 9. A laminated precursor 4 'having a structure sandwiched between 41 and 43 is formed by sputtering.
[0059]
As described above, according to the present invention, since the In layer 41 is provided on the Mo electrode 2 and the Cu—Ga alloy layer 42 is provided thereon, the element at the interface with the Mo electrode 2 can be obtained. Alloying due to solid layer diffusion can be suppressed. When the laminated precursor 4 is heat-treated in a Se atmosphere and selenized, the In component can be sufficiently diffused to the Mo electrode 2 side, and Ga having a low diffusion rate is segregated at the interface with the Mo electrode 2. Thus, a Cu—Ga—Se layer having poor crystallinity is not formed. Further, since the surface is covered with the In layer 43, Cu2Se is not generated on the surface of the light absorption layer 5 'produced by selenization.
[0060]
Therefore, there is no interposition of a different layer (Cu—Ga—Se) having poor crystallinity and being structurally brittle and having conductivity between the Mo electrode 2 and the light absorption layer 5 ′. A CIGS light absorption layer 5 ′ made of Cu (In + Ga) Se2 of a high-quality P-type semiconductor with uniform crystal without generating a conductive different layer (Cu2Se) on the surface of the light absorption layer 5 ′. It is possible to obtain a solar cell that can be fabricated, has high adhesion to the Mo electrode 2, is structurally strong, and has good battery characteristics without leakage.
[0061]
In the present invention, as shown in FIG. 11, a multilayer precursor 4 ″ is formed by providing a plurality of multi-stage structures in which a Cu—Ga alloy layer is sandwiched between In layers on a Mo electrode 2.
[0062]
Here, 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 are sequentially stacked on the Mo electrode 2. Thus, a structure in which the Cu—Ga alloy layer is sandwiched between In layers is provided in three stages.
[0063]
In this way, the In layer 41 is disposed on the Mo electrode 2 side, and the In layer 47 is disposed on the surface, and the Cu—Ga alloy layer 42, In layer 43, Cu—Ga alloy layer 44, In layer 45, and Cu—Ga are interposed therebetween. Since the alloy layer 46 is evenly distributed, it is possible to manufacture a CIGS light absorption layer 5 'made of Cu (In + Ga) Se2 of high-quality P-type semiconductor with more uniform crystals.
[0064]
FIG. 12 shows another manufacturing method of the light absorption layer 5 ′.
[0065]
Here, when forming the light absorption layer 5 ′ in a thin film solar cell using a compound semiconductor, an Ib group metal element and a IIIb group metal element are simultaneously supplied to form a single layer alloy precursor film. The formed precursor film is heat treated in a Se atmosphere to be selenized.
[0066]
Specifically, when forming the light absorption layer 5 ′ by the CIGS thin film on the Mo electrode 2 formed on the SLG substrate 1, the facing target type sputtering in which the In target T 1 and the Cu—Ga alloy target T 2 are provided is used. A sputtering process FT-SPT for forming a single-layer precursor film 10 made of a Cu—Ga—In alloy in a state where the sputtered particles of each target material are mixed on the alkali layer 9, and the precursor film 10 is made of Se. Heat treatment is performed in an atmosphere, and a heat treatment step HEAT for forming the light absorption layer 5 using a CIGS thin film is performed.
[0067]
FIG. 13 shows sputtered particles when the precursor film 10 of Cu—Ga—In alloy is formed in a state where the sputtered particles in the In target T1 and the Cu—Ga alloy target T2 are mixed by facing target type sputtering. Shows the state.
[0068]
When the In target T1 and the 2Cu—Ga alloy target T2 provided in a pair are simultaneously sputtered, particles sputtered from one target reach the other target surface. As a result, the surface of each target is mixed with the metallic elements Cu, Ga, In of both target materials, and further sputtering is performed in this state, and the sputtered particles mixed with both target materials are based. A precursor film 10 of Cu—Ga—In alloy is formed by depositing on the alkali layer 9 of the material.
[0069]
At that time, some of the In particles and Cu—Ga particles sputtered from each target T1, T2 jump out directly toward the base material without reaching the other target surface, but from the probability of the sputtered particle launch angle. Thus, the adhesion of unmixed Cu—Ga particles and In particles is very small, and the adhesion of the mixed sputtered particles to the substrate is dominant.
[0070]
According to this method, not a precursor in which an In layer and a Cu—Ga layer are stacked, but a single layer precursor in which In particles and Cu—Ga particles sputtered from the respective targets T1, T2 are mixed. Since the film 10 is formed, the metal elements of Cu, Ga, and In are uniformly arranged in the thin film as compared with the case of the laminated precursor, and the alloying promotion by the solid layer diffusion between the metal elements is promoted. It becomes possible to suppress. Further, the selenization of the precursor film 10 can be performed uniformly in the heat treatment process performed later.
[0071]
As a result, it is also effective in suppressing a heterogeneous phase (a crystal phase different from the crystal structure originally intended to be created) that causes deterioration in performance of a thin film solar cell using a compound semiconductor. In addition, the layer on which the metal precursor 3 is formed has an amorphous pseudo structure, which is a factor for obtaining a light absorption layer 5 ′ using a high-quality CIGS thin film.
[0072]
Further, since the precursor film 10 to be formed is a ternary alloy deposition structure, a short circuit as a battery is unlikely to occur.
[0073]
In addition, the precursor film 10 can be formed at high speed by simultaneous sputtering of the targets T1 and T2.
[0074]
Then, the single-layer precursor film 10 in which the metal elements of Cu, Ga, and In are thus uniformly arranged in the thin film is selenized by heat treatment in an Se atmosphere, so that high-quality Cu (In + Ga) is obtained. It becomes possible to form a light absorption layer (p-type semiconductor) 5 'using a Se2 CIGS thin film.
[0075]
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.
[0076]
FIG. 14 shows a light absorption layer 5 made of CIGS thin film from the precursor film 10 (laminated precursor 4) by causing a thermochemical reaction (vapor phase Se) by heat treatment using H2Se gas (Ar gas dilution of 5% concentration). An example of the temperature characteristic in the furnace at the time of forming 'is shown.
[0077]
Here, after the start of heating, when the furnace temperature reaches 100 ° C., preheating is performed for 10 minutes to stabilize the furnace. Then, over a period of 30 minutes as a stable ramp-up time, the temperature in the furnace is raised to 500 to 520 ° C. so that the SLG substrate 1 does not warp and can be made high quality crystals by high heat treatment. At that time, the supply of Se by thermal decomposition of H2Se gas is started from time t1 when the furnace temperature becomes 230 to 250 ° C. In order to obtain high-quality crystals by high heat treatment, heat treatment is performed for 40 minutes in a state where the furnace temperature is maintained at 500 to 520 ° C.
[0078]
At that time, from the time when the temperature in the furnace reaches 100 ° C. after the start of heating, H 2 Se gas is charged at a low temperature and heat treatment is performed while maintaining a constant pressure in the furnace. Then, at the time t2 when the heat treatment is completed, in order to prevent unnecessary precipitation of Se, the inside of the furnace is replaced with Ar gas at a low pressure of about 100 Pa.
[0079]
When the precursor film 10 is formed by facing target 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—Cu alloy. , Cu and In or Al, and Cu and In—Cu alloys. Basically, a combination of two types of an alloy of group Ib metal-group IIIb metal, group Ib metal, and group IIIb metal may be used.
[0080]
【effect】
As described above, the present invention forms a back electrode on a substrate containing an alkali component. Shi , Forming a precursor film on the back electrode, That precursor membrane When manufacturing a thin-film solar cell in which a CIGS-based light absorption layer is produced by heat treatment in an Se atmosphere and a transparent electrode is formed on the light absorption layer via a buffer layer, a back electrode and a precursor film are produced. Alkaline elements are diffused into the light absorption layer from the alkali layer and the substrate provided between the two, so that the alkali elements can be diffused into the light absorption layer efficiently and swiftly during heat treatment. become.
[0081]
In that case, according to the present invention, the diffusion control layer is formed between the substrate and the back electrode, so that the alkali element is appropriately applied to the light absorption layer without excessive supply of the alkali element of the substrate. Will be able to diffuse.
[0082]
And according to the present invention, a precursor film is formed on the back electrode in the thin film solar cell made of a compound semiconductor, That precursor membrane When manufacturing a CIGS-based light absorption layer by heat treatment in an Se atmosphere, A hydrate of a compound containing a group Ia element was dissolved. Since the back electrode is immersed in an aqueous solution and then dried to form an alkali layer on the back electrode, a layer for diffusing the alkali component of the Ia group element in the light absorption layer in order to improve energy conversion efficiency, It can be obtained by a simple process without causing problems of quality change and peeling.
[0083]
The present invention also relates to 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 alkali component, and light having an alkali element added thereto. In addition to providing an absorption layer, a diffusion control layer is provided between the substrate and the back electrode to control the diffusion of the alkali element of the substrate into the light absorption layer. With the layer, the energy conversion efficiency can be effectively improved.
[Brief description of the drawings]
FIG. 1 is a front sectional view showing a basic structure of a thin film solar cell using a general compound semiconductor.
FIG. 2 is a diagram showing a process for producing a light absorption layer on a conventional 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 for 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 light absorption layer by forming a laminated precursor on an alkali layer according to the present invention.
FIG. 6 is a characteristic diagram showing measurement results of energy conversion efficiency when a light absorption layer is produced by changing the concentration of an aqueous Na 2 S solution.
FIG. 7 is a characteristic diagram showing measurement results of energy conversion efficiency when a light absorption layer is produced by changing the liquid temperature of an Na 2 S aqueous solution.
FIG. 8 is a characteristic diagram showing measurement results of energy conversion efficiency when a light absorption layer is produced by changing the temperature at the time of baking an alkali layer.
FIG. 9 is a characteristic diagram showing a measurement result of energy conversion efficiency when a light absorption layer is produced by changing the time for baking the 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 on an alkali layer is provided in multiple stages.
FIG. 12 is a diagram showing a process for producing a light absorption layer by forming a single-layer precursor film 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 sputtering.
FIG. 14 is a diagram showing an example of heating characteristics when forming a CIGS thin film by heat-treating a precursor film in a Se atmosphere according to the present invention.
[Explanation of symbols]
1 SLG substrate
2 Mo electrode
4 Laminated precursor
5 'light absorption layer
6 Buffer layer
7 Transparent electrode
8 Diffusion control layer
9 Alkaline layer

Claims (5)

A back electrode is formed on a substrate containing an alkali component, a precursor film is formed on the back electrode, and a CIGS-based light absorption layer is produced by heat treatment in an Se atmosphere, and a buffer is formed on the light absorption layer. A method of manufacturing a thin film solar cell in which a transparent electrode is formed through a layer, wherein the back electrode is dipped in an aqueous solution in which a hydrate of a compound containing a group Ia element is dissolved, and then dried to form a transparent electrode. An alkali layer is formed on the substrate, a precursor film is formed on the alkali layer, and the precursor film is heat-treated in an Se atmosphere to produce a CIGS-based light absorption layer. A method for producing a thin-film solar cell, wherein the light-absorbing layer is diffused. The method for producing a thin-film solar cell according to claim 1 , wherein the group Ia element is Na and the alkali layer is Na2S or Na2Se . A diffusion control layer formed of SiO2, Al2O3, TiN, Si3N4, ZrO2 or TiO2 is formed between the substrate and the back electrode to control the diffusion of the alkali element of the substrate into the light absorption layer . A method for producing a thin-film solar cell according to claim 1 . 4. The method of manufacturing a thin-film solar cell according to claim 3 , wherein the film thickness of the diffusion control layer is in the range of 100 to 1500 mm . ^{2. The} method of manufacturing a thin-film solar cell according to claim 1, wherein the concentration of the group Ia element diffused in the light absorption layer is in the range of 10E + 10 to 10E + 16 atoms per 1 cm ^{2 of} unit area .

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