JPH11135819A - Compound thin-film solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solar cell which restrains the thermal deformation and the thermal strain of a substrate in an element formation process and whose reliability is high, and to restrain its production cost in a thin-film photoelectric conversion element, in which a Cu(In, Ga)Se2 -based or CdTe-based compound semiconductor is used as a photoelectric conversion layer. SOLUTION: A glass substrate 11 is used. Since its composition and its manufacturing method are similar to those of a soda lime glass, its production cost is low. The annealing point of the glass substrate 11 is at 620 deg.C, and it is higher than the highest process temperature (550 deg.C) of the formation of a solar cell. In addition, the coefficient of thermal expansion of a glass is at 8×10<-6> / deg.C, and it nearly matches with the coefficient of thermal expansion of a CIGS absorption layer. An Mo electrode 12 is used. A Cu(In,Ga)Se2 thin film 13 is formed through a vapor deposition method. A ZnO film 15 and an ITO transparent conductive film 16 are used. A extraction electrode 17 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compound thin-film solar cell using a photoelectric conversion layer containing a group Ib, group IIIb or group VIb element formed on a glass substrate as a main component.

[0002]

2. Description of the Related Art Ib-III having chalcopyrite crystal structure
Group b-VIb compound semiconductors and cubic or hexagonal IIb
-VIb group compound semiconductors are expected to be used as materials for high-efficiency thin-film solar cells because they have a large absorption coefficient for light in the visible to near-infrared wavelength range. Representative examples include Cu (In, Ga) Se ₂ system (hereinafter referred to as CIGS system) and CdTe system. In CIGS system, alumina or quartz glass or
Beginning with a thin film on a corning 7059 glass substrate,
At present, thin film solar cells on soda lime glass substrates are mainly studied. Research on soda-lime glass is inexpensive and its thermal expansion coefficient is close to that of CIS-based compound semiconductors, so research is proceeding at the practical level, and high-efficiency solar cells have been achieved. Also, research on CdTe was started with alumina and quartz glass, and soda lime glass was also studied as with CIGS. Research has mainly been conducted using corning7059 glass as a substrate, and has also reached a practical level.

[0003]

However, soda lime glass has a low softening temperature, and when forming an absorption layer of a CIGS solar cell, the substrate temperature is close to the softening point of the glass. However, there are problems such as deformation due to non-uniform application of force caused by supporting the substrate only at the outer periphery. To address this problem, generally non-alkali glass having a high softening point such as cornering7059 glass or low alkali glass having an alkali content of less than 1% was used.However, these glasses have a thermal expansion coefficient with the absorption layer. Due to the large difference, the absorption layer and the like are distorted, causing problems such as frequent peeling and generation of voids in the film, and a solar cell with high efficiency was not finally obtained.

In the case of CdTe-based solar cells, soda-lime glass was not used because the formation temperature was somewhat higher than CIGS. Corning 7059 glass, which has a high softening point, was mainly used. There was a disadvantage that it was disadvantageous.

[0005] Although the viscosity of glass continuously decreases when heated, there are a strain point, an annealing point, and a softening point as temperatures that are indicators of the thermal characteristics of glass. The strain point is a temperature below which the strain in the glass cannot be removed, and the annealing point is the temperature at which the internal strain of the glass is removed in 15 minutes.In other words, it is easily deformed by the application of external force. Is the temperature at which The softening point is literally the temperature at which the glass begins to soften and deform under its own weight without applying any force. It has been found that the slow cooling point of glass serves as an index when considering the distortion in growing a crystal of CIGS or CdTe on a glass substrate.

[0006] In view of the above, an object of the present invention is to provide a solar cell which is inexpensive and has little deformation and thermal distortion.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention has a gradual cooling point higher than 550 ° C. and a glass having a thermal expansion coefficient of at least 6 × 10 ⁻⁶ / ° C. and at least 10 × 10 ^6. A solar cell having a CIGS-based compound or CdTe provided on a glass substrate having a temperature of ^-6 / C or lower as an absorption layer.

In the above structure, the content of SiO ₂ is 40% by weight or more and 80% by weight or less, the content of Al ₂ O ₃ is 5% by weight or more and 15% by weight or less, and Na ₂ O, K ₂ O Content of each 1
Not less than 15% by weight and MgO, CaO, SrO, BaO,
It is preferable to use glass having a Zr ₂ O content of 1% by weight or more and 10% by weight or less.

Further, in the above structure, the content of SiO ₂ is
58 ± 10% by weight, Al ₂ O ₃ , Na ₂ O, K ₂ O, MgO, CaO, Sr
O, BaO, Zr ₂ O content of 7 ± 2, 4 ± 1, 6 ± 2, 2 respectively
It is further preferable to use glass having a content of ± 1, 5 ± 1, 7 ± 2, 8 ± 2, 2 ± 1% by weight.

Further, in the above structure, it is preferable that the thermal expansion coefficients of the glass and the absorbing layer match within an error of 10% or less.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

<First Embodiment of the Invention> FIG. 1 shows the structure of a solar cell according to the present invention. It is a so-called substrate type.

Reference numeral 11 denotes a glass substrate. 12 is a Mo electrode. 13 is a CIGS thin film formed by a vapor deposition method. 14 is CdS, 1
5 is ZnO and 16 is an ITO transparent conductive film. 17 is an extraction electrode. The annealing point of the glass substrate is higher than the process temperature for forming the solar cell. The ratio of the thermal expansion coefficient of the absorption layer to the thermal expansion coefficient of the glass substrate is 0.6 or more.
1.4 or less.

Hereinafter, a specific manufacturing method will be described. (Example 1) A glass substrate of the above composition having a thickness of 30 mm and a thickness of 1 mm
11 (annealing point is 620 ° C) is washed with a commercially available alkaline glass washing solution. After rinsing with pure water, the back surface Mo electrode 12 is formed to about 1 μm by RF sputtering. The sputtering gas is nitrogen. Hereinafter, the process proceeds with a part of the Mo electrode masked. First, while the substrate temperature was raised to about 550 ° C., copper, indium, gallium, and metallic selenium were simultaneously vapor-deposited to form a CIGS polycrystalline thin film 13 of 2 μm.
The atomic ratio of Cu, In, Ga, and Se in the CIGS film is 1: 0.75:
0.25: 2. Thereafter, 14 CdS was formed to a thickness of about 0.1 μm by a chemical bath deposition method (CBD method). In the case of this example, a mixture of cadmium chloride, ammonium chloride, thiourea, and ammonia at a ratio of about 1: 10: 1: 100 was heated to about 80 ° C., and the substrate was inserted into the mixture and crystallized. Further, about 15 microns of ZnO and about 16 microns of ITO were respectively formed by sputtering. The sputtering gas at this time is nitrogen.
Finally, with the mask in place, gold 17 as an extraction electrode was formed by an evaporation method. The composition of the glass substrate is similar to soda lime glass (SLG), but SrO, BaO, Z
Including rO, etc., the annealing point is higher than that of general soda lime glass, and higher than the process temperature for forming this solar cell. The components are shown in Table 1. SiO ₂ , Al ₂ O ₃ , Na
The contents of ₂ O, K ₂ O, MgO, CaO, SrO, BaO, and Zr ₂ O are 58, 7, 4, 6, ₂ , 5, 7, 8, and 1% by weight, respectively. The amount of distortion of the solar cell thus formed was measured. FIG. 2 shows a top view (upper side) and a side view (lower side) before and after element formation when soda lime glass of a conventional example is used. (A) is before element formation and (b) is after element formation. 30.0mm square substrate is short arc 28.9mm long arc 31.0mm width 29.9 after element formation
Deformed into a fan shape of mm. This is a deformation that occurred because the process temperature exceeded the annealing point and internal strain was relaxed. Also, when viewed from the side, after the element was formed, it was deformed into an arc shape as if a sphere was cut out, and the displacement at the center was 0.3 mm. This is a deformation caused by holding the substrate only at the end of the 30 mm square substrate and applying an upward force only to the end because the process temperature has exceeded the annealing point. In contrast to these examples, in the solar cell of the present invention, there was almost no deformation of the substrate before and after element formation, and all were within 0.1 mm for a 30 mm square substrate. In this solar cell, the maximum temperature of the process is 550 ° C at the time of CIGS deposition, while the annealing point of the glass substrate is as high as 620 ° C. It is formed.

[0015] In the solar cell, an absorption layer is provided.
The thermal expansion coefficient of CIGS is 8 × 10 ^-6 / ° C, and the glass substrate 11
^Is approximately the same as the thermal expansion coefficient (8 × 10 ⁻⁶ / ° C.). Therefore, the thermal expansion coefficient distortion is very small.

As described above, according to the present invention, it is possible to reduce the deformation and the deterioration of the element characteristics due to the deformation. As a result, the yield can be improved, and the cost of element production can be reduced. In addition, about 10% of the case where the conventional soda lime glass was used for peeling of the film considered to be caused by stress due to deformation was 1% in the solar cell of the present invention.
And the yield can be improved.

FIG. 3 shows current-voltage characteristics of the solar cell at the time of light irradiation. The element size is 1 cm square, and the light irradiation condition is AM1.5 which is used as a standard for evaluation of solar cells. Almost the same performance as the conventional characteristics is obtained.

Although a 30 mm square glass substrate was used in the present invention, the effect of the present invention became more remarkable as the substrate size increased.

Here, in FIG. 11, the annealing point having the components shown in Table 1 is 620.
° C glass was used, but other than this, the content of SiO ₂
40 wt% or more and 80 wt% or less, the content of Al ₂ O ₃ is 5 wt% or more and 15 wt% or less, and the content of Na ₂ O and K ₂ O is 1 wt% or more and 15 wt% or less, respectively. And MgO, CaO, Sr
O, BaO, Zr ₂ O content is 1wt% or more and 10wt% respectively
A solar cell having a CIGS-based compound as an absorption layer prepared on a glass having a cooling point higher than 550 ° C. and a thermal expansion coefficient of the glass of 6 × 10 ⁻⁶ / ° C. or more and 10 × 10 ⁻⁶ / ° C or lower, and a similar effect of reducing deformation and distortion was observed because the coefficient of thermal expansion was relatively close to the absorption layer. Since this glass is similar in composition and manufacturing method to soda-lime glass, the technique of manufacturing soda-lime glass can be used as it is, and thus the substrate manufacturing cost is as low as soda-lime glass.

[0020]

[Table 1]

Here, the content of SiO ₂ is particularly 58 ± 10% by weight, and Al ₂ O ₃ , Na ₂ O, K ₂ O, MgO, CaO, SrO, BaO, Zr
₂ O content of 7 ± 2, 4 ± 1, 6 ± 2, 2 ± 1, 5 ± 1,
7 ± 2,8 ± 2,2 ± 1 wt% CI formed on glass
In the case of a solar cell having a GS compound as the absorption layer, the annealing point of the glass is as high as 600 ° C. or higher, and the thermal expansion coefficient of the glass is about 8 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the CIGS absorption layer And the effect of reducing deformation and distortion was particularly large.

Here, the glass of other components has an annealing point higher than 550 ° C. and a thermal expansion coefficient of 6 × 10 5
^In the case of a solar cell having a CIGS-based compound formed on a glass substrate having a temperature of ^-6 / ° C or more and 10 × 10 ^-6 / ° C or less, there was an effect of reducing deformation and distortion. Specific examples
Similar effects were observed when a substrate containing 5% of SnO ₂ without containing Zr ₂ O with respect to the substrate used in 1 was obtained. In particular, when the thermal expansion coefficients of the glass and the absorbing layer coincide with each other within an error of 10%, the effect of reducing the deformation was great.

In this embodiment, the substrate type CIGS solar cell has been described. However, a similar effect can be obtained also in a so-called superstrate type in which the glass substrate has a different position.

<Embodiment 2> FIG. 4 shows the structure of a solar cell according to the present invention. It is a so-called super straight type.

Reference numeral 41 denotes a glass substrate. The components are examples
42, which is the same as the glass substrate used in 1, is a fluorine-doped SnO ₂ transparent conductive film, 43 is n-type CdS, and 44 is p-type CdTe. 45 is a carbon electrode, and 46 is silver as an extraction electrode. Numeral 47 denotes an Ag-In electrode as a take-out electrode. As in Embodiment 1, the annealing point of the glass substrate is higher than the process temperature for forming the solar cell. The ratio of the coefficient of thermal expansion of the absorbing layer to the coefficient of thermal expansion of the glass substrate is 0.6 or more and 1.4 or less.

Hereinafter, a specific manufacturing method will be described. (Example 2) A glass substrate of the above composition having a thickness of 30 mm square and a thickness of 1 mm
41 (annealing point: 620 ° C.) is washed with the same alkaline glass washing solution as in Example 1. After the rinsing treatment, 42 fluorine-containing SnO ₂ of about 0.5 μm was formed by RF sputtering. The sputtering gas is a nitrogen gas containing 5% of fluorine. Below this SnO
_The process proceeds with part of ₂ masked. First,
By CBD method, 43 CdS was formed to about 0.1 μm. In the case of this embodiment, a mixture of cadmium chloride, ammonium chloride, thiourea, and ammonia at a ratio of about 1: 10: 1: 100 is used for about 80 hours.
The substrate was inserted into the substrate by heating to ℃ to crystallize n-type CdS. Next, 44 μm of p-type CdTe was formed to 4 μm by proximity sublimation. At this time, the substrate temperature, the raw material temperature, and the degree of vacuum were 600 ° C., 680 ° C., and 100 Torr, respectively. Then carbon 45
Is deposited by EB, and finally, the mask is replaced and the Ag electrode 46 and the Ag
-In electrode 47 was EB deposited.

The amount of distortion of the solar cell thus formed was measured. When the conventional Corning 7059 glass was used, the deformation amount of the element viewed from above and before and after the element formation and the deformation amount viewed from the side were 0.1 mm or less in the case of a 30 mm square substrate, whereas the present invention Similarly, the amount of deformation of the solar cell element was within 0.1 mm. The unit price of glass of the present composition is about 1/10 that of corning7059 glass, and the cost can be reduced according to the present invention.

FIG. 5 shows current-voltage characteristics of the solar cell at the time of light irradiation. The element size is 1 cm square, and the light irradiation condition is AM1.5 which is used as a standard for evaluation of solar cells. Almost the same performance as the conventional characteristics is obtained.

In this solar cell, the maximum temperature of the process is 600 ° C. during the formation of the CdTe film, whereas the annealing temperature of the glass substrate is as high as 620 ° C. A device having no defect is formed. In this solar cell, the thermal expansion coefficient of CdTe as the absorption layer is 5 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the glass substrate 41 (8
× 10 ⁻⁶ / ° C). For this reason, the thermal expansion coefficient distortion is relatively small, and the influence on the element is small. Since this glass is similar in composition and manufacturing method to soda-lime glass, the technique of manufacturing soda-lime glass can be used as it is, and thus the substrate manufacturing cost is as low as soda-lime glass.

As described above, according to the present invention, it is possible to suppress the deterioration of the device characteristics due to the deformation and the distortion, and to use the inexpensive substrate for the cornin.
Since element characteristics similar to those of g7059 can be obtained, element manufacturing costs can be reduced.

Although a 30 mm square glass substrate was used in the present invention, the effect of the present invention became more remarkable as the substrate size increased.

Here, glass having the components shown in Table 1 was used for 41, but other than this, the content of SiO ₂ was 40% by weight or more and 80% or more.
% By weight, the content of Al ₂ O ₃ is 5% by weight or more and 15% by weight or less, the content of Na ₂ O and K ₂ O is 1% by weight or more and 15% by weight or less, respectively, MgO, CaO, SrO, BaO, solar cell using CdTe-based compound formed on a glass and the absorbent layer is that not more than 10 wt%, respectively 1 wt% or more the content of Zr ₂ O is anneal points higher than 550 ° C. Comparable to process temperature,
And the coefficient of thermal expansion of the glass is 6 × 10 ⁻⁶ / ° C. or more and 10 × 10 ^−6.
/ ° C. or less, which is relatively close to the coefficient of thermal expansion of the CdTe film, so that the effect of reducing the manufacturing cost while similarly suppressing the deformation and distortion was observed.

Here, the content of SiO ₂ is particularly 58 ± 10% by weight, and Al ₂ O ₃ , Na ₂ O, K ₂ O, MgO, CaO, SrO, BaO, Zr
₂ O content of 7 ± 2, 4 ± 1, 6 ± 2, 2 ± 1, 5 ± 1,
7 ± 2,8 ± 2,2 ± 1% by weight formed on glass substrate
In the case of a solar cell using a CdTe-based compound as the absorption layer, the annealing point of the glass is as high as 600 ° C or higher, and the coefficient of thermal expansion of the glass is about 8 × 10 ^-6 / ° C. Compared to the coefficient of thermal expansion of the CdTe film Because of their closeness, the effect of reducing manufacturing costs while suppressing deformation and distortion was significant.

Here, the glass of other components has an annealing point higher than 550 ° C. and a thermal expansion coefficient of 6 × 10 5
^In the case of a solar cell having a CdTe-based compound formed on a glass substrate having a temperature of ^-6 / ° C or more and 10 × 10 ^-6 / ° C or less,
This has the effect of reducing manufacturing costs while suppressing deformation and distortion. Specifically, the same effect was observed when a substrate containing 5% of SnO ₂ without containing Zr ₂ O with respect to the substrate used in Example 1. In particular, the thermal expansion coefficient of the glass and the absorption layer is
%, The effect of reducing deformation was large.

In this embodiment, the superstrate type CdTe-based solar cell has been described. However, the same effect can be obtained also in the case of a substrate type having a different position of the glass substrate.

[0036]

As described in the above embodiments, the present invention has the following advantageous effects.

In a solar cell provided on a glass substrate and having a copper-indium-gallium-selenium compound or cadmium tellurium as an absorption layer, the glass has an annealing point of 55
Higher than 0 ° C and the thermal expansion coefficient of glass is 6 × 10 ^-6 /
When the temperature is not less than 10 ° ^C./° C. and not more than 10 × 10 ⁻⁶ / ° C., deformation of the substrate due to thermal history and distortion of the thin film due to a difference in thermal expansion coefficient can be suppressed. As a result, the yield is improved, and the substrate manufacturing cost can be kept low. Therefore, there is an effect that the element manufacturing cost can be reduced.

Here, the content of SiO ₂ is from 40% by weight to 80% by weight, and the content of Al ₂ O ₃ is from 5% by weight to 15% by weight.
And the content of Na ₂ O and K ₂ O is 1% by weight or more, respectively.
15% by weight or less, MgO, CaO, SrO, BaO, and Zr ₂ O content of 1% by weight or more and 10% by weight or less, respectively, the annealing point is higher than 550 ° C, and the thermal expansion coefficient of glass The above effect is large because the temperature is 6 × 10 ⁻⁶ / ° C. or more and 10 × 10 ⁻⁶ / ° C. or less.

Here, the SiO 2 in the glass_TwoContent of 58
± 10% by weight, Al_TwoO_Three, Na_TwoOK _TwoO, MgO, CaO, Sr
O, BaO, Zr_TwoO content is 7 ± 2, 4 ± 1, 6 ± 2, 2 respectively
Slow cooling when ± 1, 5 ± 1, 7 ± 2, 8 ± 2, 2 ± 1% by weight
Is 600 ° C or higher and the coefficient of thermal expansion of the glass is
7 × 10^-6/ ℃ or more 9 × 10^-6/ ° C or lower and CIGS thermal expansion
The above effect is very large because the
Good.

Here, when the coefficients of thermal expansion of the glass and the absorbing layer match within an error of 10% or less, the effect of suppressing thermal distortion is great.

As described above, according to the present invention, when obtaining a CIGS or CdTe solar cell, the deformation of the substrate due to the thermal history, the distortion due to the difference in the coefficient of thermal expansion, and the low manufacturing cost are achieved. It is possible and practically very useful.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a CIGS solar cell of the present invention.

FIG. 2 is a diagram of deformation of a CIGS solar cell of the present invention before and after element formation.

FIG. 3 is a diagram showing current-voltage characteristics during light irradiation of the CIGS solar cells of the present invention and a conventional example.

FIG. 4 is a structural diagram of a CdTe-based solar cell of the present invention.

FIG. 5 is a diagram showing current-voltage characteristics of a CdTe-based solar cell of the present invention and a conventional example during light irradiation.

[Explanation of symbols]

11 glass substrate (component Table 1) 12 Mo electrode 13 Cu (In, Ga) Se 2 thin film 14 CdS 15 ZnO 16 ITO transparent conductive film 17 extraction electrode (Au) 41 glass substrate (component Table 1) 42 fluorine added SnO ₂ Transparent conductive film 43 n-type CdS 44 p-type CdTe 45 carbon electrode 46 extraction electrode (Ag) 47 extraction electrode (Ag-In)

Continuation of the front page (72) Inventor Takahiro Wada 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A solar cell having a copper-indium-gallium-selenium compound or cadmium tellurium as an absorption layer provided on a glass substrate, wherein the glass has an annealing point higher than 550 ° C. Expansion coefficient is 6 ×
10 ^-6 / ° C. or higher 10 × 10 ^-6 / ℃ or less compound thin film solar cell. _2. The content of SiO ₂ is 40% by weight or more and 80% by weight or less, the content of Al ₂ O ₃ is 5% by weight or more and 15% by weight or less, and the content of Na ₂ O and K ₂ O is _{2. 2.} The compound according to claim 1, wherein the glass is used in an amount of 1% by weight or more and 15% by weight or less, and a content of each of MgO, CaO, SrO, BaO, and Zr2O is 1% by weight or more and 10% by weight or less. Thin-film solar cells. 3. The composition according to claim 1, wherein the content of SiO ₂ is 58 ± 10% by weight,
The contents of ₂ O ₃ , Na ₂ O, K ₂ O, MgO, CaO, SrO, BaO, and Zr ₂ O are respectively 7 ± 2, 4 ± 1, 6 ± 2, 2 ± 1, 5 ± 1, 7 ± 2, 8 ± 2,
2. The compound thin film solar cell according to claim 1, wherein the glass is 2 ± 1% by weight. 4. The method according to claim 1, wherein the coefficient of thermal expansion of the glass and the absorption layer is 10
2. The compound thin-film solar cell according to claim 1, wherein the coincidence is within%.