JP2013084664A - Solar battery manufacturing method, and solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method which allows the manufacture of a solar battery having an excellent power generation efficiency.SOLUTION: The method is for manufacturing a solar battery which has a lower electrode, a light absorption layer containing Cu, In, Ga and Se, a buffer layer, a transparent conductive layer, and an upper electrode, which are formed on a glass substrate at least in this order. The light absorption layer is formed by executing, on the lower electrode: a first step where Se and Ga are deposited at a substrate temperature of 300-500°C; a second step where Se and In are deposited at a substrate temperature of 300-500°C; a third step where the substrate temperature is raised from the temperature in the second step to a temperature of 550-630°C, and then Se and Cu are deposited; a fourth step where Se and In are deposited at a substrate temperature of 550-630°C; and a fifth step where Se and Ga are deposited at a substrate temperature of 550-630°C, at least in this order.

Description

  The present invention relates to a solar cell manufacturing method and a solar cell.

The Ib-IIIb-VIb group compound semiconductor having a chalcopyrite crystal structure and the cubic or hexagonal type IIb-VIb group compound semiconductor have a large absorption coefficient for light in the visible to near-infrared wavelength range. It is expected as a material for high-efficiency thin-film solar cells. Typical examples include Cu (In, Ga) Se ₂ system (hereinafter referred to as CIGS system) and CdTe system.

  In the CIGS solar cell, for example, a MoGS is formed on a soda lime glass substrate, and then a CIGS layer is formed on the Mo electrode. As a CIGS layer forming method, a multi-source deposition method in which a CIGS layer is formed by simultaneously evaporating Cu, In, Ga, and Se by a multi-source deposition apparatus (see, for example, Patent Documents 1 and 2), and a Cu-Ga alloy. A selenization method is known in which a laminated precursor film composed of a Cu—Ga alloy layer and a pure In layer is formed by sputtering using a target and an In target, and this is heat-treated in a selenium atmosphere (see, for example, Patent Document 3). ).

JP-A-11-135819 International Publication No. 2011/049146 Pamphlet JP-A-10-135498

  FIG. 14 shows a conventional CIGS layer forming process, and shows a forming process of a three-stage method which is a kind of multi-source deposition method. In the three-stage method, first, as the first stage, Ga, In, and Se are vapor-deposited simultaneously at a substrate temperature of about 400 ° C. Further, as the second stage, Cu and Se are vapor-deposited at a substrate temperature of about 500 to 550 ° C. Further, as the third stage, the substrate temperature is set to about 500 to 550 ° C., and Ga, In, and Se are again vapor-deposited again.

  In formation of such a CIGS layer, in order to manufacture the solar cell which is more excellent in power generation efficiency, performing vapor deposition of a CIGS layer at high temperature is examined. By performing the deposition of the CIGS layer at a high temperature, defects in the CIGS layer are reduced, and an improvement in power generation efficiency is expected.

  However, when the conventional three-step method is simply performed at a high temperature, Ga is likely to diffuse, and the Ga concentration distribution in the CIGS layer, particularly the concentration distribution in the thickness direction, is likely to be uniform. When the Ga concentration distribution is uniform, even if the light absorption wavelength region is narrowed and defects in the CIGS layer are reduced, improvement in power generation efficiency cannot be expected.

  The present invention has been made to solve the above-described problems, and can manufacture a solar cell that can form an appropriate Ga concentration distribution in the CIGS layer and has excellent power generation efficiency even when vapor deposition is performed at a high temperature. The purpose is to provide a method. Another object of the present invention is to provide a solar cell in which an appropriate Ga concentration distribution is formed in the CIGS layer and the power generation efficiency is excellent.

  In the method for manufacturing a solar cell of the present invention, a lower electrode, a light absorption layer containing Cu, In, Ga, and Se, a buffer layer, a transparent conductive layer, and an upper electrode are formed at least in this order on a glass substrate. The present invention relates to a method for manufacturing a solar cell. The method for manufacturing a solar cell according to the present invention particularly includes a first step of depositing Se and Ga on the lower electrode at a substrate temperature of 300 to 500 ° C., and Se and In at a substrate temperature of 300 to 500 ° C. A second step of vapor deposition; a third step of raising the substrate temperature from the temperature in the second step to 550 to 630 ° C. and depositing Se and Cu; and a substrate temperature of 550 to 630 ° C. and Se and The light absorbing layer is formed by performing at least a fourth step of depositing In and a fifth step of depositing Se and Ga at a substrate temperature of 550 to 630 ° C. in this order.

The solar cell of the present invention relates to a solar cell in which a lower electrode, a light absorption layer containing Cu, In, Ga, and Se, a buffer layer, a transparent conductive layer, and an upper electrode are formed at least in this order on a glass substrate. . In the solar cell of the present invention, in particular, the light absorption layer is Cu _x (In _1-y Ga _y ) Se _z (0.7 ≦ x ≦ 1.0, 0.1 ≦ y ≦ 0.6, 9 ≦ z ≦ 2.0), and a count of Ga in the range from the upper principal surface to 700 nm in the thickness direction by secondary ion mass spectrometry, having a chalcopyrite type crystal structure. The percentage ratio of the minimum value of the Ga count number in the entire range in the thickness direction from the upper main surface to the lower main surface with respect to the maximum value is 4 to 40%.

  According to the method for manufacturing a solar cell of the present invention, the step of depositing Ga and the step of depositing In are basically performed in separate steps, and the first step of depositing Ga is the first In. The step of depositing Ga for the second time and the step of depositing Ga for the second time are performed after the step of depositing In for the second time, and the steps of depositing Ga for the second time are performed separately from each other. An appropriate Ga concentration distribution can be formed in the light absorption layer, and a solar cell excellent in power generation efficiency can be manufactured.

  In addition, according to the solar cell of the present invention, in particular, the thickness direction from the upper main surface to the lower main surface with respect to the maximum value of the Ga count in the range from the upper main surface to 700 nm in the thickness direction. By setting the percentage ratio of the minimum value of the count number of Ga in the entire range of 4 to 40%, the Ga concentration distribution in the light absorption layer can be made appropriate and high power generation efficiency can be obtained.

Sectional drawing which shows one Embodiment of the solar cell manufactured by the manufacturing method of this invention. The figure which shows one Embodiment of the formation process of the light absorption layer in the manufacturing method of this invention. The figure which shows collectively the relationship between the etching time by SIMS of the light absorption layer in Examples 1-5 and the solar cell of the comparative example 1, and the count number of Ga. The figure which shows collectively the relationship between the etching time by SIMS of the light absorption layer in the solar cell of Comparative Examples 1-4, and the count number of Ga. The figure which shows the result of Example 1 in FIG. 3 independently. The figure which shows the result of Example 2 in FIG. 3 independently. The figure which shows the result of Example 3 in FIG. 3 independently. The figure which shows the result of Example 4 in FIG. 3 independently. The figure which shows the result of Example 5 in FIG. 3 independently. The figure which shows the result of the comparative example 1 in FIG. 4 independently. The figure which shows the result of the comparative example 2 in FIG. 4 independently. The figure which shows the result of the comparative example 3 in FIG. 4 independently. The figure which shows the result of the comparative example 4 in FIG. 4 independently. The figure which shows an example of the formation process of the light absorption layer by the conventional three-step method.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a cross-sectional view showing one embodiment of a solar cell manufactured by the manufacturing method of the present invention. In the solar cell 1, for example, a lower electrode 3, a light absorption layer 4 containing Cu, In, Ga, and Se, a buffer layer 5, a transparent conductive layer 6, and an upper electrode 7 are at least in this order on a glass substrate 2. It is formed.

  FIG. 2 is a process diagram showing an embodiment of a process for forming the light absorption layer 4. The light absorption layer 4 has a first step of depositing Se and Ga on the lower electrode 3 with a substrate temperature of 300 to 500 ° C., and a second step of depositing Se and In with a substrate temperature of 300 to 500 ° C. A third step of evaporating Se and Cu by raising the substrate temperature from the temperature in the second step to 550 to 630 ° C., and a fourth step of evaporating Se and In at a substrate temperature of 550 to 630 ° C. And the fifth step of depositing Se and Ga at a substrate temperature of 550 to 630 ° C. is performed at least in this order.

  Although the film formation time is shown in FIG. 2, the film formation time in the present invention is not necessarily limited to this. In addition, the substrate temperature between steps, for example, the substrate temperature between steps in the first step to the second step, and the substrate temperature between steps in the third step to the fifth step are not necessarily the same. It can be different for each process within the above range. Further, the substrate temperature in each process is not necessarily the same, and can be varied within the above-described range.

  According to the above manufacturing method, the step of vapor-depositing Ga and the step of vapor-depositing In are basically divided into separate steps, and the step of vapor-depositing Ga for the first time is a step of vapor-depositing In the first time. The step of evaporating Ga for the second time is performed after the step of evaporating In for the second time, and the step of evaporating Ga for the second time is performed so as to be separated from each other. It is easy to form a portion with a high Ga concentration near both of the main surfaces, and to form a portion with a low Ga concentration between them.

  Therefore, even if Ga is diffused by performing vapor deposition at a high temperature, a sufficient Ga concentration distribution can be formed, and the effect of reducing defects caused by performing vapor deposition, which is the original purpose, at a high temperature can be sufficiently obtained. A solar cell having excellent power generation efficiency can be manufactured. In addition, when the conventional three-stage method is simply performed at high temperature, the effect of reducing defects caused by vapor deposition at high temperature is canceled out by uniformizing the Ga concentration distribution by diffusion of Ga, resulting in excellent power generation efficiency. A solar cell cannot be manufactured.

  The light absorption layer 4 is formed by dividing the Ga vapor deposition step and the In vapor deposition step into separate steps, as described above, and the Ga vapor deposition step and the In vapor deposition step in a predetermined order. Except that the temperature of the substrate is higher than that of the prior art, and can be carried out by an apparatus basically similar to the conventional three-stage method.

That is, the formation of the light absorption layer 4 is usually performed by using Cu _x (In _1-y Ga _y ) Se _z (0.7 ≦ x ≦ 1.0, 0.1 ≦ y ≦ 0.6, 1. 9 ≦ z ≦ 2.0), a known multi-source vapor deposition apparatus, for example, a vacuum chamber, a substrate heater disposed in the vacuum chamber, Cu, In, Ga, and Se deposition sources, It can carry out using a multi-source vapor deposition apparatus provided with.

  Each vapor deposition source may be disposed in a crucible, or a boat or the like may be used instead of the crucible. Moreover, the glass substrate 2 on which the lower electrode 3 on which the light absorption layer 4 is formed is disposed on, for example, a substrate stage that incorporates a substrate heater.

The light absorption layer 4 preferably contains only Cu, In, Ga, and Se. However, if necessary and within the limits of the gist of the present invention, Si, Al, Mg, and Ca are additionally added. , Sr, Ba, Li, Na, K, B, Zr and La may contain at least about 1 × 10 ³⁰ at / cc.

Each process is performed by adjusting to a predetermined substrate temperature while controlling the pressure with an ionization vacuum gauge, for example. The pressure of each element at the time of vapor deposition is, for example, the Se pressure in the first step is 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻² Pa, and the Ga pressure is 1 × 10 ⁻⁵ Pa to 1 × 10 ^−4. Pa, Se pressure in the second step is 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻² Pa, In pressure is 1 × 10 ⁻⁵ Pa to 1 × 10 ⁻⁴ Pa, Se in the third step The pressure is 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻² Pa, the pressure of Cu is 1 × 10 ⁻⁶ Pa to 1 × 10 ⁻⁴ Pa, and the pressure of Se in the fourth step is 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻² Pa, In pressure is 1 × 10 ⁻⁵ Pa to 1 × 10 ⁻⁴ Pa, Se pressure in the fifth step is 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻² Pa, Ga The pressure is preferably 1 × 10 ⁻⁵ Pa to 1 × 10 ⁻⁴ Pa.

  The film formation time in each step can be appropriately selected so that the total thickness of the light absorption layer 4 is about 1 to 3 μm and an optimum band cap can be obtained. The process is 600 to 3600 seconds, the second process is 600 to 3600 seconds, the third process is 600 to 3600 seconds, the fourth process is 300 to 1800 seconds, and the fifth process is 300 to 1800 seconds.

  The substrate temperature in each step is not necessarily limited as long as it is within the above range, but the substrate temperature in the first step is preferably 350 to 450 ° C, and the substrate temperature in the second step is preferably 350 to 450 ° C. The substrate temperature in the third step is preferably 580 to 610 ° C, the substrate temperature in the fourth step is preferably 580 to 610 ° C, and the substrate temperature in the fifth step is preferably 580 to 610 ° C. By increasing such a substrate temperature, in particular, the substrate temperature in the third to fifth steps, the effect of reducing defects in the light absorption layer 4 can be sufficiently obtained, and the solar cell excellent in power generation efficiency Can be manufactured.

In the first process, only Se and Ga, in the second process, only Se and In, in the third process, only Se and Cu, in the fourth process, only Se and In, and in the fifth process, Se and Ga. However, as long as it is necessary and does not violate the spirit of the present invention, for example, in the first step, In is additionally added at 1 × 10 ⁻⁵ Pa to 1 × 10 ^−. It may be deposited at a pressure of ⁴ Pa for about 1 to 500 seconds. In the second step, Ga is additionally deposited at a pressure of 1 × 10 ⁻⁵ Pa to 1 × 10 ⁻⁴ Pa for about 1 to 500 seconds. In the fourth step, Ga may be additionally deposited at a pressure of 1 × 10 ⁻⁵ Pa to 1 × 10 ⁻⁴ Pa for about 1 to 250 seconds. In the fifth step, additional Ga may be added. pressure of ^{1 × 10 -5 Pa~1 × 10 -4} Pa to in the In may be deposited about 1 to 250 seconds.

  The light absorption layer 4 may be formed by performing only the first to fifth steps described above. However, after the fifth step, the sixth is to deposit Se and In at a substrate temperature of 550 to 630 ° C. It is preferable to perform this process. By adding such a sixth step, the open-circuit voltage (Voc) can be increased by improving the band gap connection between the light absorption layer 4 and the buffer layer 5, and as a result, a solar cell having excellent power generation efficiency can be obtained. Can be manufactured.

The pressure of the sixth step definitive Se is ^{1 × 10 -4 Pa~1 × 10 -2} Pa, the pressure of In ^{1 × 10 -5 Pa~1 × 10 -4} Pa is preferred. The treatment time in the sixth step is preferably 1 to 120 seconds. The effect can be effectively obtained by setting the processing time in the sixth step to 1 second or more. Further, it is sufficient that the processing time in the sixth step is 120 seconds, and productivity can be improved by setting it to be less than this. The treatment time in the sixth step is more preferably 1 to 90 seconds, and further preferably 1 to 60 seconds.

  In addition, after the fifth step or when performing the sixth step, it is preferable to perform a seventh step of performing heat treatment at 550 to 630 ° C. in an Se atmosphere after the sixth step. In the first to fifth steps or the first to sixth steps described above, Se defects may occur in the light absorption layer 4 due to re-evaporation of Se. In the case where the fifth step or the sixth step is performed, Se defects in the light absorption layer 4 can be reduced by performing a heat treatment at 550 to 630 ° C. in an Se atmosphere after the sixth step. .

The pressure of the Se atmosphere in the seventh step is preferably 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻² Pa. The treatment time in the seventh step is preferably 1 to 10 minutes. By setting the processing time in the seventh step to 1 minute or longer, Se defects can be effectively reduced. Further, if the treatment time in the seventh step is 10 minutes, Se defects can be sufficiently reduced, and productivity can be improved by setting it to be less than this. The treatment time in the seventh step is more preferably 2 to 8 minutes, and further preferably 3 to 7 minutes.

  According to the above manufacturing method, at least the first step to the fifth step, in particular, the step of depositing Ga and the step of depositing In are performed by dividing them into separate steps, thereby performing deposition at a high temperature. Even in this case, an appropriate Ga concentration distribution can be formed in the light absorption layer 4.

  Specifically, the thickness from the upper main surface to the lower main surface with respect to the maximum value of the Ga count in the range from the upper main surface to 700 nm in the thickness direction by secondary ion mass spectrometry (SIMS). Percentage ratio of the minimum value of Ga count number in the entire range in the direction ((minimum value of Ga count number) / (maximum value of Ga count number) × 100 [%]) within a range of 4 to 40% can do. The upper side means the buffer layer 5 side, and the lower side means the lower electrode 3 side.

  By setting it as such Ga concentration distribution, the absorption wavelength range of light can fully be widened, and the fall of power generation efficiency can be suppressed. The ratio is more preferably in the range of 5 to 30%, and still more preferably in the range of 5 to 20%.

  Next, other members and constituent layers of the solar cell 1 will be described.

  As the glass substrate 2, one having a thickness in the range of 0.5 to 6 mm is suitably used, the composition thereof is not particularly limited, and the glass transition temperature is higher than soda lime glass plate and soda lime glass, and Since there is much alkali elution amount, the glass plate etc. which can improve electric power generation efficiency can be used.

As a glass plate having a glass transition temperature higher than that of soda lime glass and having a large amount of alkali elution, for example, in terms of oxide-based molar percentage, SiO ₂ : 60 to 75%, Al ₂ O ₃ : 3 to 10%, _{B 2 O 3: 0~3%,} MgO: 5~18%, CaO: 0~5%, Na 2 O: 4~18.5%, K 2 O: 0~17%, SrO + BaO + ZrO 2: 0~10 %, K ₂ O / (Na ₂ O + K ₂ O) is 0 to 0.5, and the glass transition temperature (Tg) exceeds 550 ° C.

SiO ₂ is a component that forms a glass skeleton. If it is less than 60%, the heat resistance and chemical durability of the glass are lowered, and the thermal expansion coefficient may be increased. However, if it exceeds 75%, the high-temperature viscosity of the glass increases, which may cause a problem that the meltability deteriorates. It is preferably 63 to 72%, more preferably 63 to 70%, and still more preferably 63 to 69%.

Al ₂ O ₃ increases the glass transition temperature, improves weather resistance (solarization), heat resistance and chemical durability, and increases Young's modulus. If the content is less than 3%, the glass transition temperature may be lowered and the thermal expansion coefficient may be increased. However, if it exceeds 10%, the high-temperature viscosity of the glass increases, the meltability may deteriorate, the devitrification temperature increases, and the moldability may deteriorate. In addition, the power generation efficiency may be reduced, that is, the amount of alkali elution described later may be reduced. The content is preferably 4 to 9%, more preferably 5 to 8%.

B ₂ O ₃ may be contained up to 3% in order to improve the meltability. When the content exceeds 3%, the glass transition temperature decreases or the thermal expansion coefficient decreases, which is not preferable for the manufacturing process of the solar cell 1, particularly for the process of forming the light absorption layer 4. More preferably, the content is 2% or less. The content is particularly preferably 1.5% or less.

If the total amount of SiO ₂ , Al ₂ O ₃ , and B ₂ O ₃ is large, the alkali elution is inhibited, so that the smaller amount is preferable. The total amount of SiO ₂ , Al ₂ O ₃ , and B ₂ O ₃ is preferably 80% or less, more preferably 78% or less, further preferably 75% or less, and particularly preferably 73% or less.

  MgO is contained because it has the effect of lowering the viscosity at the time of melting the glass and accelerating the melting, but if it is less than 5%, the high temperature viscosity of the glass may increase and the meltability may deteriorate, and the power generation efficiency may be reduced. There is a risk that the decrease, that is, the amount of alkali elution described later will decrease. However, if it exceeds 18%, the thermal expansion coefficient may increase and the devitrification temperature may increase. It is preferably 6 to 16%, more preferably 7 to 14%, and still more preferably 8 to 12%.

  CaO can be contained because it has an effect of reducing the viscosity at the time of melting the glass and promoting the melting. However, if the content exceeds 5%, the power generation efficiency decreases, that is, the amount of alkali elution described later decreases, and the thermal expansion coefficient of the glass plate may increase. It is preferably 3% or less, more preferably 2% or less, and further preferably 1% or less.

  SrO can be contained because it has the effect of lowering the viscosity at the time of melting the glass and promoting the melting. However, if the content exceeds 5%, the power generation efficiency decreases, that is, the amount of alkali elution described later decreases, and the thermal expansion coefficient of the glass plate may increase. It is preferably 4% or less, and more preferably 3% or less.

  BaO can be contained because it has the effect of reducing the viscosity at the time of melting the glass and promoting the melting. However, if it exceeds 4%, the power generation efficiency decreases, that is, the amount of alkali elution described later decreases, and the thermal expansion coefficient of the glass plate may increase. It is preferably 3% or less, and more preferably 2% or less.

ZrO ₂ can be contained because it has the effects of lowering the viscosity at the time of melting the glass, increasing the power generation efficiency, and promoting the melting. However, if the content exceeds 4%, the power generation efficiency decreases, that is, the amount of alkali elution described later decreases, and the thermal expansion coefficient of the glass plate may increase. 3% or less is preferable.

SrO, BaO and ZrO ₂ are contained in a total amount of 0 to 10% in order to lower the viscosity at the melting temperature of the glass and facilitate melting. However, if the total amount exceeds 10%, the power generation efficiency decreases, that is, the amount of alkali elution described later decreases, and the glass transition point temperature decreases and the glass thermal expansion coefficient may increase. The total amount of SrO, BaO, and ZrO ₂ is preferably 1% or more, more preferably 2% or more. It is preferably less than 10%, more preferably 9% or less, and further preferably 8% or less.

Na ₂ O is a component that contributes to improving the conversion efficiency of a CIGS solar cell, and is an essential component. Moreover, since there exists an effect which lowers | hangs the viscosity in glass melting temperature and makes it easy to melt | dissolve, 4 to 18.5% is contained. Na diffuses into the light absorption layer 4 to increase the conversion efficiency. However, if the content is less than 4%, the Na diffusion into the light absorption layer 4 is insufficient, and the conversion efficiency may be insufficient. The content is preferably 5% or more, more preferably 6% or more, even more preferably 7% or more, and particularly preferably 10% or more. When the Na ₂ O content exceeds 18.5%, the coefficient of thermal expansion increases, or the chemical durability deteriorates. The content is preferably 17.5% or less, the content is more preferably 16.5% or less, the content is more preferably 15.5% or less, and the content is 14% or less. Particularly preferred.

Since K ₂ O has the same effect as Na ₂ O, 0 to 17% is contained. However, if it exceeds 17%, the power generation efficiency is lowered, that is, the amount of alkali elution described later is lowered, the glass transition temperature is lowered, and the thermal expansion coefficient may be increased. When it contains, it is preferable that it is 1% or more. It is preferably 12% or less, more preferably 9% or less, and even more preferably 7% or less.

Na ₂ O and _{K 2} O, to lower the viscosity at the glass melting temperature sufficiently, the ratio of the value of _{K 2} O content of for the total amount of Na ₂ O and _{K 2 O [K 2 O /} (Na ₂ O _{+ K 2} O)] to 0 to 0.5. If it exceeds 0.5, the power generation efficiency decreases, that is, the amount of alkali elution described later decreases, and the thermal expansion coefficient may increase or the solubility may decrease. K ₂ O / (Na ₂ O + K ₂ O) is preferably 0.1 or more. 0.45 or less is preferable, 0.4 or less is more preferable, and 0.35 or less is more preferable. Na ₂ O and K ₂ O are preferably contained in a total amount of 13 to 20%. It is more preferably 19.5% or less, further preferably 19% or less, and particularly preferably 18.5% or less. The total amount of Na ₂ O and K ₂ O is more preferably 14% or more, and further preferably 15% or more.

The value of the ratio of the total amount of Na ₂ O and K ₂ O to the total amount of SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ [(Na ₂ O + K ₂ O) / (SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ )] Is preferred because it promotes alkali elution. (Na ₂ O + K ₂ O) / (SiO ₂ + Al ₂ O ₃ + B ₂ O ₃ ) is preferably 0.15 or more, more preferably 0.18 or more, and further preferably 0.20 or more. Yes, particularly preferably 0.22 or more.

The glass plate preferably consists essentially of the mother composition, but may contain other components typically 5% or less in total. For example, ZnO, Li ₂ O, WO ₃ , Nb ₂ O ₅ , V ₂ O ₅ , Bi ₂ O ₃ , MoO ₃ , P ₂ for the purpose of improving weather resistance, meltability, devitrification, and ultraviolet shielding. O ₅ may be contained in some cases.

Further, in order to improve the solubility and clarity of the glass, these raw materials may be added to the matrix composition raw material so that the total amount of SO ₃ , F, Cl, SnO ₂ is 2% or less in the glass. Good. Further, in order to improve the chemical durability of the glass, ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ , TiO ₂ and SnO ₂ may be contained in the glass in a total amount of 5% or less. Among these, Y ₂ O ₃ , La ₂ O ₃ , and TiO ₂ contribute to the improvement of the Young's modulus of the glass. TiO ₂ can also contribute to the improvement of power generation efficiency.

Further, in order to adjust the color tone of the glass, it may contain a colorant such as Fe ₂ O ₃ in the glass. The total content of such colorants is preferably 1% or less.

Further, the glass plate is, considering the environmental _burden, it is preferred not to contain _{As 2 O 3, Sb 2 O} 3 substantially. In consideration of stable float forming, it is preferable that ZnO is not substantially contained.

  As for the said glass plate, it is preferable that the amount of alkali elution is 0.15 or more by the calculated value of Na / In intensity ratio by secondary ion mass spectrometry (SIMS). More preferably, it is 0.2 or more. Moreover, it is preferable that the alkali elution amount is 1E + 20 or more in terms of the amount of Na in the Mo film by SIMS: unit atoms / cc. More preferably, it is 1.5E + 20 or more, More preferably, it is 2.0E + 20 or more, Most preferably, it is 2.5E + 20 or more. The amount of K in the Mo film by SIMS is preferably 1E + 18 or more in units of atoms / cc. More preferably, it is 1E + 19 or more, More preferably, it is 3E + 19 or more, Most preferably, it is 5E + 19 or more.

The said glass plate can be manufactured by implementing a melt | dissolution and clarification process and a shaping | molding process similarly to the conventional glass plate. In addition, since the above glass plate is an alkali glass substrate containing an alkali metal oxide (Na ₂ O, K ₂ O), SO ₃ can be effectively used as a refining agent, and a float method is used as a forming method. Suitable for

  First, molten glass obtained by melting raw materials is formed into a plate shape. For example, a raw material is prepared so that it may become the composition of the glass plate obtained, the said raw material is continuously thrown into a melting furnace, and it heats to about 1450-1650 degreeC, and obtains molten glass. The molten glass is formed into a ribbon-like glass plate by applying, for example, a float process. Next, after drawing the ribbon-shaped glass plate from the float forming furnace, it is cooled to room temperature by a cooling means and cut to obtain a glass plate.

When forming the lower electrode 3 or its underlying layer (for example, SiO ₂ ) on the surface of the glass substrate 2, the glass substrate 2 may not be formed normally if the surface of the glass substrate 2 is dirty. It is preferable to wash. The washing method is not particularly limited, and examples include washing with water, washing with a cleaning agent, and rubbing with a brush or the like while spraying a slurry containing cerium oxide. In the case of washing with a cerium oxide-containing slurry, it is preferably washed with an acidic detergent such as hydrochloric acid or sulfuric acid. It is preferable that the glass plate surface after washing does not have irregularities or the like on the glass plate surface due to dirt or deposits such as cerium oxide. If there is unevenness, unevenness on the surface of the film, film thickness deviation, pinholes in the film, and the like may occur during film formation, which may reduce power generation efficiency. The unevenness is preferably 20 nm or less with a height difference.

Moreover, when providing the alkali metal supply layer mentioned later, as the glass substrate 2, what contains only a small amount of alkali metals, for example, an alkali free glass may be sufficient. Note that the alkali-free glass, in terms of _oxide, the sum of _{Li 2 O + Na 2 O +} K 2 O refers to 0.1 mass% of glass.

Examples of the alkali-free glass include SiO ₂ : 50 to 66%, Al ₂ O ₃ : 10.5 to 22%, B ₂ O ₃ : 0 to 12%, MgO: 0 in terms of mass percentage based on oxide. -8%, CaO: 0 to 14.5%, SrO: 0 to 24%, BaO: 0 to 13.5%, and MgO + CaO + SrO + BaO: 9 to 29.5% by mass.

  The lower electrode 3 is made of, for example, Mo, Ti, Al, or Cr. The thickness of the lower electrode 3 is preferably 100 to 1000 nm. If the film thickness of the lower electrode 3 becomes excessively thick, the adhesion with the glass substrate 2 may be reduced. Moreover, when the film thickness of the lower electrode 3 becomes excessively thin, the electrical resistance increases. The formation method of the lower electrode 3 is not particularly limited, and examples thereof include a sputtering method, a vapor deposition method, and a vapor deposition method (PVD, CVD).

Between the glass substrate 2 and the lower electrode 3, or between the lower electrode 3 and the light absorbing layer 4, or between the glass substrate 2 and the lower electrode 3, and between the lower electrode 3 and the light absorbing layer 4, or below An alkali metal supply layer for improving the power generation efficiency by diffusing the alkali metal into the light absorption layer 4 in the electrode 3 can be provided. The alkali metal supply layer may be made of a compound such as Na ₂ S, Na ₂ Se, NaCl, or NaF, but is made of a niobium oxide containing an alkali metal, for example, a compound such as LiNbO ₃ , NaNbO ₃ , or KNbO _3. Is preferred. Since the niobium oxide containing an alkali metal is stable in the air and hardly dissolves in water, the handling property at the time of manufacturing the solar cell 1 can be improved and the durability can be improved. LiNbO _3, Of NaNbO _3, KNbO _3, sintered NaNbO ₃ is, the melting point is _highest, compared with LiNbO 3, KNbO _3, used for film formation because it sintered choose hot sintering temperature The sputtering target is particularly preferable because it can be easily produced at a high density.

  The buffer layer 5 is made of, for example, a compound containing Cd or Zn that forms a semiconductor layer. Examples of the compound containing Cd include CdS, and examples of the compound containing Zn include ZnO, ZnS, ZnMgO, and the like. Although not shown, the buffer layer 5 may be composed of a plurality of semiconductor layers. In this case, the first layer on the side close to the light absorption layer 4 is made of the compound containing CdS or Zn as described above, and the second layer on the side far from the light absorption layer 4 is ZnO or It is comprised with the material containing ZnO. Although the film thickness of the buffer layer 5 is not specifically limited, 50-300 nm is preferable.

  The transparent conductive layer 6 is made of a material such as ZnO or ITO, for example. Alternatively, these materials may be doped with a group III element such as Al. The transparent conductive layer 6 may be configured by laminating a plurality of layers. The thickness of the transparent conductive layer 6 (total thickness in the case of a plurality of layers) is not particularly limited, but is preferably 100 to 3000 nm.

  The transparent conductive layer 6 is further electrically connected to an upper electrode 7 that is a conductive extraction member. The upper electrode 7 is preferably made of, for example, one or more metals selected from Ni, Cr, Al, and Ag.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
A glass substrate (soda lime glass plate) processed to a 3 cm × 3 cm square and a thickness of 1.1 mm was immersed in a beaker containing an acetone solution, and the substrate was cleaned with an ultrasonic cleaner at room temperature for 5 minutes. Similarly, the substrate was cleaned with an ethanol solution, and the same substrate surface was cleaned with each of a new acetone solution and ethanol solution. Thereafter, the solution was blown off with a nitrogen gun and dried.

On this glass substrate, a molybdenum layer as a lower electrode was formed by sputtering using a sputtering apparatus (manufactured by TOKKI). The film formation conditions were as follows: heating before pre-deposition 120 ° C., 1 minute, power 4.0 W / cm ² , argon flow rate 80 sccm, film formation pressure 0.3 Pa, and reciprocating twice to form a molybdenum layer having a thickness of about 800 nm. .

  In the sample exchange chamber of the multi-source deposition apparatus, the glass substrate with a molybdenum layer was heated at 200 ° C. for 30 minutes to remove moisture and impurities on the surface of the substrate. Thereafter, a light absorption layer was formed on the molybdenum layer so as to have a thickness of 1.8 μm or more using a multi-source deposition apparatus (manufactured by EpiQuest) as follows.

First, the substrate temperature was heated to about 400 ° C., and Ga and Se were evaporated from the deposition source to deposit Ga and Se on the surface of the molybdenum layer (first step (first Ga-Se deposition step)). . Under the present circumstances, the vapor pressure of Se was measured with the ionization vacuum gauge, and it was set as the conditions of 1 * 10 ^{< -3} > ^-1 * 10 ^<-2 > Pa. And using the radiation thermometer, light was irradiated to the film | membrane surface formed by vapor deposition, the interference fringe of light was observed with the radiation thermometer, and vapor deposition was performed until the period became 3/4.

  After the deposition of Ga and Se, In and Se were evaporated from the deposition source while maintaining the substrate temperature at 400 ° C., and In and Se were deposited on the molybdenum layer surface (second step (first In— Se deposition process)). Using a radiation thermometer, light was irradiated onto the surface of the film formed by vapor deposition, and interference fringes of light were observed by the radiation thermometer, and vapor deposition was performed until the period became 2 and 3/4.

  After the deposition of In and Se, the substrate temperature was raised by heating, and Cu and Se were evaporated from the deposition source to perform the deposition of Cu and Se (third step). Heating was performed until the substrate temperature reached 600 ° C., and when the temperature reached 600 ° C., the temperature was kept constant. Cu and Se were deposited until the composition of the entire film on the molybdenum layer was excessive Cu. Whether Cu is excessive or not was determined by using a radiation thermometer and confirming a waveform change due to a change in physical properties. The deposition time for Cu and Se was 1.3 times the time from the start of deposition to the waveform change point.

  After the deposition of Cu and Se, In and Se were evaporated from the deposition source to deposit In and Se (fourth step (second In-Se deposition step)). The deposition time of In and Se was 0.4 / 2 times the total deposition time of the first Ga-Se deposition process and the first In-Se deposition process.

  After vapor deposition of In and Se, Ga and Se were evaporated from the vapor deposition source to perform vapor deposition of Ga and Se (fifth step (second Ga-Se vapor deposition step)). The deposition time of Ga and Se was set to 0.4 / 2 times the total deposition time of the first Ga-Se deposition process and the first In-Se deposition process.

As described above, Cu _x (In _1-y Ga _y ) Se _z (0.7 ≦ x ≦ 1.0, 0.1 ≦ y ≦ 0.6, 1.9 ≦ z ≦ 2.0) Light having In and Ga in excess with respect to Cu with respect to the stoichiometric composition ratio of CIGS (Cu / (In + Ga) <1) and having a thickness of 1.8 to 2 μm An absorption layer was formed.

  Thereafter, the glass substrate with the light absorption layer was immersed in a 10% strength potassium cyanide solution for 60 seconds and washed to remove the CuSe layer that causes leakage current. Then, it was washed twice with pure water in a beaker, dried by blowing off moisture with a nitrogen gun.

  Next, a CdS layer was formed on the light absorption layer by a CBD (Chemical Bath Deposition) method. The film forming conditions are as follows: 0.015M cadmium sulfate, 1.5M thiourea, and 15M ammonia aqueous solution are mixed in a beaker with a magnetic stirrer and an ultrasonic cleaner, and immersed in a constant temperature bath whose water temperature is 80 ° C. in advance. When the temperature was stabilized, the substrate was put in and a CdS layer was formed to a thickness of 50 to 100 nm while stirring with a magnetic stirrer. Thereafter, the substrate was transferred into pure water placed in a beaker, washed with an ultrasonic cleaner, further washed with pure water prepared in another beaker, and dried by blowing off moisture with a nitrogen gun.

A ZnO layer is formed on the CdS layer by a sputtering apparatus (manufactured by ANELVA) using a ZnO target, and an AZO target (a ZnO target containing 1.5 wt% of Al ₂ O ₃ ) is further formed thereon. An AZO layer was deposited using it. The film forming conditions were as follows: power 2.46 W / cm ² , film forming pressure 0.7 Pa, Ar flow rate 10 sccm, ZnO with a thickness of about 100 nm at room temperature, and AZO with a thickness of about 200 nm thereon.

An Al electrode having a thickness of about 1 μm was formed on the AZO layer. The film formation was performed by a heat vapor deposition method with 99.999% aluminum material placed on a heating boat. For film formation, a stencil mask processed into the shape of an electrode was used. Then, using a pointed metal plate, the light absorption layer is scraped off, the lower electrode is left as a cell, and the lower electrode is fabricated, and a certain area (the area excluding the Al electrode is about 0.5 cm ² ) A solar cell in which a total of 8 cells were arranged on each side with 4 cells on both sides was produced.

[Example 2]
In the formation of the light absorption layer, the Ga and Se vapor deposition time in the fifth step (second Ga-Se vapor deposition step) is shortened by 10 seconds, and instead, In and Se vapor deposition is performed for 10 seconds (the sixth). Example 1), except that the substrate temperature was kept at 600 ° C. for 5 minutes in the Se atmosphere (Se pressure 3 × 10 ⁻³ to 1 × 10 ⁻² Pa) (seventh step). A solar cell was produced in the same manner as described above.

[Example 3]
In the formation of the light absorption layer, a solar cell was produced in the same manner as in Example 1 except that the Se pressure was approximately doubled (1 × 10 ^{−2 to} 1.6 × 10 ⁻² Pa) throughout the process. did.

[Example 4]
In the formation of the light absorption layer, the deposition time of Ga and Se in the fifth step (second Ga-Se deposition step) is shortened by 10 seconds, and instead, In and Se are deposited for 10 seconds (first step). A solar cell was produced in the same manner as in Example 1 except that the Se pressure was doubled (1 × 10 ^{−2 to} 1.6 × 10 ⁻² Pa) throughout the entire process.

[Example 5]
In film formation of the light absorption layer, the substrate temperature was further maintained at 600 ° C. for 5 minutes in the Se atmosphere (Se pressure 3 × 10 ⁻³ to 1 × 10 ⁻² Pa) (seventh step). A solar cell was produced in the same manner as in Example 1.

[Comparative Example 1]
A CIGS solar cell was produced in the same manner as in Example 1 except that the light absorption layer was formed by the conventional three-stage method as shown below.

The substrate was heated to about 400 ° C., and In, Ga, and Se were evaporated from the deposition source, and In, Ga, and Se were deposited on the surface of the molybdenum layer (first stage). At this time, the vapor pressure of Se was measured with an ionization vacuum gauge and adjusted to 5 × 10 ⁻³ to 8 × 10 ⁻³ Pa. Then, using an “Infrared Thermometer KTL-PRO series non-contact / infrared radiation thermometer” (hereinafter referred to as a radiation thermometer) manufactured by LEC Company Limited, the film surface formed by vapor deposition is irradiated with light, and the radiation thermometer emits light. Interference fringes were observed and deposition was performed until the period was 2 and 3/4.

  After the deposition of In, Ga, and Se, the substrate was heated, and at the same time, Cu and Se were evaporated from the deposition source to perform the deposition of Cu and Se (second stage). Heating was performed until the substrate temperature reached 520 ° C., and after reaching 520 ° C., the temperature was maintained at 520 ° C. Cu and Se were deposited until the composition of the entire film on the molybdenum layer was excessive Cu. Whether Cu is excessive or not was determined by measuring a change in waveform due to a change in physical properties using a radiation thermometer. The second stage deposition time was 1.3 times the time from the start of the second stage deposition to the waveform change point.

  After the deposition of Cu and Se, In, Ga, and Se were evaporated from the deposition source to deposit In, Ga, and Se (third stage). The deposition time for the third stage was 0.4 times the deposition time for the first stage.

As described above, Cu _x (In _1-y Ga _y ) Se _z (0.7 ≦ x ≦ 1.0, 0.1 ≦ y ≦ 0.6, 1.9 ≦ z ≦ 2.0) Light having In and Ga in excess with respect to Cu with respect to the stoichiometric composition ratio of CIGS (Cu / (In + Ga) <1) and having a thickness of 1.8 to 2 μm An absorption layer was formed.

[Comparative Example 2]
A solar cell was fabricated in the same manner as in Comparative Example 1 except that the substrate temperature in the second and third stages was set to 600 ° C. in the formation of the light absorption layer.

[Comparative Example 3]
A solar cell was fabricated in the same manner as in Comparative Example 1 except that the substrate temperature in the second and third stages was set to 650 ° C. in the formation of the light absorption layer.

[Comparative Example 4]
A solar cell was fabricated in the same manner as in Example 1 except that the substrate temperature was set to 520 ° C. in the steps after the deposition of Cu and Se (third step) in the formation of the light absorption layer.

  Tables 1 and 2 collectively show the film forming processes of the light absorption layers of Examples and Comparative Examples.

  Next, the following measurements were performed on the solar cells of Examples and Comparative Examples.

[Measurement of battery efficiency of solar cells]
Prepare a container with a side of about 30cm that can block external light from entering the interior, paint the inside of the container in black to suppress reflection of light inside the container, and install solar cells in the container did. In addition, the solar cell has a positive terminal on the molybdenum layer previously coated with InGa solvent (for ohmic contact), a negative terminal on the Al electrodes on the eight cell surfaces, and a voltage / current generator (device name: R6243, Connected to ADVANTEST).

  And it controlled with the temperature regulator so that the temperature in a container might be 25 degreeC. External light was blocked in the container, and a xenon lamp (USHI) was irradiated from the upper part of the battery for 10 seconds. Thereafter, the temperature of the battery was stabilized by holding for 60 seconds. Thereafter, the voltage was changed from −1 V to +1 V at an interval of 0.015 V when the xenon lamp was not irradiated and when it was irradiated, and the current value was measured. The power generation efficiency was calculated from the current and voltage characteristics during irradiation.

The power generation efficiency was determined by the following formula (1) from the open circuit voltage (Voc), the short circuit current density (Jsc), and the fill factor (FF).
Power generation efficiency [%] = Voc [V] × Jsc [mA / cm ² ] × FF [Dimensionless] × 100
/ Illuminance [W / cm ² ] of the light source used for the test (1)

  Here, the open circuit voltage (Voc) is an output when the terminal is opened, and the short circuit current density (Jsc) is obtained by dividing the short circuit current (Isc), which is a current when the terminal is shorted, by the effective area. Yes, the fill factor (FF) is the product of the voltage at the maximum output point (maximum voltage value (Vmax)) and the current at the maximum output point (maximum current value (Imax)), which is the point that gives the maximum output. (Voc) divided by the product of the short circuit voltage (Isc).

[Measurement of Ga concentration distribution]
Distribution measurement was performed in the thickness direction from the upper side of the light absorption layer by secondary ion mass spectrometry (SIMS). The measurement apparatus used was “ADEPT1010” manufactured by ULVAC-PHI, and the measurement conditions were primary ion: O ₂ ⁺ , acceleration voltage: 5 kV, and beam current: 700 nA.

  Tables 3 and 4 collectively show the results of the power generation efficiency and Ga concentration distribution of the solar cells of Examples and Comparative Examples. 3 and 4 show Ga concentration distribution profiles (relationship between SIMS etching time and Ga count). 3 and 4 collectively show the profiles of the Ga concentration distributions of the example and the comparative example, respectively, and FIGS. 5 to 13 show the Ga of the example and the comparative example shown in FIGS. The profile of density distribution is shown individually.

  As is clear from Tables 3 and 4 and FIGS. 3 to 13, an appropriate Ga concentration distribution can be obtained for the solar cells of Examples 1 to 5 in which the predetermined film forming process is performed and the predetermined substrate temperature is set. It can be seen that high power generation efficiency can be obtained. It can also be seen that higher power generation efficiency can be obtained by performing the sixth step of depositing In and Se, or the seventh step of maintaining in the Se atmosphere.

  On the other hand, in the solar cells of Comparative Examples 2 and 3 in which the substrate temperature is simply increased in the conventional film formation process, the Ga concentration distribution is made uniform, that is, the minimum value / maximum value becomes excessively large, and thus high power generation efficiency. In the solar cell of Comparative Example 4 in which the substrate temperature is lowered, the Ga concentration distribution is excessively formed, that is, the minimum value / maximum value is excessively small. Therefore, it can be seen that high power generation efficiency cannot be obtained.

  DESCRIPTION OF SYMBOLS 1 ... Solar cell, 2 ... Glass substrate, 3 ... Lower electrode, 4 ... Light absorption layer, 5 ... Buffer layer, 6 ... Transparent conductive layer, 7 ... Upper electrode

Claims (4)

On a glass substrate
Bottom electrode,
A light absorbing layer containing Cu, In, Ga, and Se,
Buffer layer,
Transparent conductive layer,
And a method of manufacturing a solar cell in which at least the upper electrode is formed in this order,
The light absorbing layer is
A first step of depositing Se and Ga at a substrate temperature of 300 to 500 ° C .;
A second step of depositing Se and In at a substrate temperature of 300 to 500 ° C .;
A third step of evaporating Se and Cu by raising the substrate temperature from the temperature in the second step to 550 to 630 ° C .;
A fourth step of depositing Se and In at a substrate temperature of 550 to 630 ° C .;
And a fifth step of depositing Se and Ga at a substrate temperature of 550 to 630 ° C. at least in this order on the lower electrode.   The method for manufacturing a solar cell according to claim 1, wherein after the fifth step, a sixth step of depositing Se and In at a substrate temperature of 550 to 630 ° C is performed.   3. The seventh step of performing a heat treatment at 550 to 630 ° C. in a Se atmosphere after the fifth step or after the sixth step when performing the sixth step. 4. A method for manufacturing a solar cell. A solar cell in which a lower electrode, a light absorbing layer containing Cu, In, Ga, and Se, a buffer layer, a transparent conductive layer, and an upper electrode are formed on a glass substrate at least in this order,
The light absorption layer is Cu _x (In _1-y Ga _y ) Se _z (0.7 ≦ x ≦ 1.0, 0.1 ≦ y ≦ 0.6, 1.9 ≦ z ≦ 2.0). The upper main layer with respect to the maximum count number of Ga in the range from the upper main surface to 700 nm in the thickness direction by secondary ion mass spectrometry, comprising a compound having a chalcopyrite type crystal structure having the composition shown A solar cell, characterized in that the percentage of the minimum value of the Ga count number in the entire range in the thickness direction from the surface to the lower principal surface is 8 to 70%.

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