JP2002009307A - Method for manufacturing solar battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solar battery with high conversion efficiency where the contact resistance between hetero layers in a solar battery, and further resistance in the crosswise direction of a semiconductor layer has been reduced. SOLUTION: In a process after composing a sub module, light with illuminance exceeding 100,000 lux, or preferably 150,000 lux is applied from the light reception surface side of the sub module.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solar cell.

[0002]

2. Description of the Related Art Since the first oil crisis in 1973, solar cells have been expected as an alternative energy source for fossil energy. In the 1990's, solar cells have come to have much higher expectations as an energy source corresponding to global environmental problems. However, until the practical use of solar cells, there are many problems to be solved, such as high conversion efficiency and low cost. A solar cell includes at least one pair of semiconductor layers having p-type and n-type characteristics, and an electrode layer electrically connected to the semiconductor layers, and these different types of semiconductor layers and electrode layers are stacked. Is formed. If the adhesion between these different layers is incomplete, electrical contact failure occurs, and a solar cell with high performance and long-term reliability cannot be obtained. This is a problem caused by crystal defects in the semiconductor. In the case where the semiconductor layer is polycrystalline, an electric barrier present at a grain boundary in the polycrystal increases the resistance of the semiconductor in the surface direction, which is a factor of deteriorating the performance of the solar cell. Therefore, solving these problems is an important issue in aiming for high conversion efficiency of a solar cell.

[0003] Compound semiconductors other than Si semiconductors have been put to practical use as semiconductors constituting solar cells. As a typical solar cell using a compound semiconductor, CdS / CdTe using cadmium telluride (CdTe) for a p-type semiconductor and cadmium sulfide (CdS) for an n-type semiconductor, respectively.
There is a system solar cell, which is manufactured as follows. First,
Indium oxide (IT) on a light-transmitting substrate such as a glass substrate
A transparent conductive film such as O) and a CdS thin film are sequentially formed. Next, a CdTe film is formed on the CdS film. Further, C
A carbon film is formed on the dTe thin film, and then AgIn is formed on the exposed surface of the transparent conductive film or the CdS film and on the carbon film.
The sub-module of the solar cell is formed by forming the film.
This submodule may be composed of a single cell, but usually, a plurality of cells are formed on the glass substrate by scribing each of the above films in a predetermined pattern,
These cells are electrically connected by an AgIn electrode or the like.

As a method for forming a CdS film and a CdTe film, a proximity sublimation method, a vacuum evaporation method, a sputtering method, a solution growth method, an organic metal compound thermal decomposition method, and the like have been proposed or implemented. Usually, the CdS film or CdTe film obtained by these methods takes a polycrystalline form. When the contact state between the crystal grains at the grain boundary of the polycrystalline body is insufficient, this becomes an electrical barrier that inhibits conductivity, and this increases the resistance component in the plane direction in the solar cell. In addition, the presence of crystal defects in the film increases the contact resistance between the layers. The increase in these resistances reduces the fill factor of the solar cell, and further reduces the current collection efficiency of sunlight-induced current, thereby reducing the short-circuit current density. ,

In order to address the above-mentioned problems, various conditions such as a film forming temperature, a film forming time, and an atmosphere for forming each constituent film during a manufacturing process of a polycrystalline compound semiconductor solar cell are optimized. I have been. In order to improve the crystallinity of the semiconductor layer, for example, measures such as applying a heat treatment after applying a solution of a melting point depressant such as cadmium chloride to a CdTe film have been taken. However, at present, the above-mentioned problems have not been solved to a satisfactory state by only these conventional methods.

In addition to polycrystalline compound semiconductor solar cells such as CdS / CdTe, compound semiconductor cells such as gallium-arsenic, amorphous, single crystal, etc.
Also in each of the polycrystalline silicon solar cells, insufficient electrical contact between different layers due to crystal defects in the semiconductor layer is a major obstacle to improving solar cell performance. At present, a method capable of effectively solving the above problem has not been developed.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems that hinder the improvement of the performance of a solar cell and to provide a method for manufacturing a solar cell with high conversion efficiency.

[0008]

According to a method of manufacturing a solar cell of the present invention, an n-type semiconductor layer and a p-type semiconductor layer are formed by lamination, and the n-type semiconductor layer and the p-type semiconductor layer are electrically connected to each other. After forming a submodule provided with a series of electrodes, a step of irradiating light having an illuminance of 100,000 lux or more, preferably 150,000 lux or more from the light receiving surface side of the submodule is provided. . Thereby, the conversion efficiency of various solar cells including polycrystalline compound semiconductor solar cells such as CdS / CdTe solar cells can be greatly improved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing a solar cell according to the present invention comprises:
A work-in-progress (final process) in which a pn junction is formed by laminating and forming an n-type semiconductor layer and a p-type semiconductor layer on a substrate and further forming an electrode layer electrically connected to each of the semiconductor layers ( 100,000 from the light-receiving surface side of a so-called sub-module, that is, a single module on which electrodes are formed on a substrate, or a plurality of cells electrically connected by electrodes on a substrate. A step of irradiating light with an illuminance of lux or more is provided. The step of irradiating the light may be provided at any timing after the sub-module is formed and before a solar cell (module) is completed using the sub-module.

According to the present invention, the film quality is improved by removing crystal defects in each semiconductor layer in a solar cell, and the contact resistance between different layers (between semiconductor layers or between a semiconductor layer and an electrode layer) is reduced. Can be done. In addition, when applied to a polycrystalline compound semiconductor solar cell, in addition to the above effects,
Removing electrical barriers present at grain boundaries in the semiconductor layer,
In particular, the effect of reducing the resistance component in the plane direction is added.
These effects are due to the fact that the crystal in the semiconductor layer is rearranged by the absorption energy of the irradiation light, thereby removing crystal defects and reducing the interlayer contact resistance, and at the same time improving the contact state of the crystal grain boundaries. It is thought to be.

[0011] By the above operation and effect, among the output characteristics of the solar cell, particularly, the fill factor and the short-circuit current are improved, whereby the conversion efficiency of the solar cell can be increased. In addition, according to the present invention, the performance of each unit cell in a sub-module formed on the same substrate can be improved and the variation can be reduced, so that the conversion efficiency of a large-area solar cell in which many unit cells are connected in series can be improved. It can be improved effectively. Further, the present invention can provide a great effect by a simple method of irradiating the sub-module with light, thereby contributing to cost reduction of the solar cell.

Solar cells are broadly classified into silicon-based solar cells and compound semiconductor solar cells, and the present invention can be applied to all of these solar cells. Among silicon-based solar cells, there are single-crystal silicon solar cells, polycrystalline silicon solar cells, and amorphous silicon solar cells. Among compound semiconductor solar cells, GaAs / Si, InP / Si,
Single crystal type such as GaAs / Ge and III-V group or II-V
There are polycrystalline types such as group I and chalcopyrite. Among the above, when the present invention is applied to a polycrystalline compound semiconductor solar cell, a particularly large effect can be obtained for the above-described reason.

FIG. 1 is a cross-sectional view of a CdS / CdTe solar cell as an example of a polycrystalline compound semiconductor solar cell, and an embodiment of the present invention will be specifically described with reference to the drawing.
First, a transparent conductive film 2 is formed on a transparent substrate 1 such as a glass substrate.
Is formed, and a CdS film 3 as an n-type semiconductor layer is formed on the film.
To form Next, after the transparent conductive film and the CdS film are simultaneously scribed and divided into a predetermined pattern, a CdTe film 4 as a p-type compound semiconductor layer is formed thereon. Further, a solution of a melting point depressant is applied to the p-type semiconductor layer, and heat treatment is performed at 300 to 500 ° C. for 5 to 60 minutes.

Next, after the heat-treated CdTe film 4 is scribed into a predetermined pattern and divided into single cells, a carbon electrode 5 is formed on each of the divided CdTe films 4.
The carbon electrode 5 can be formed by applying a carbon paste by screen printing, drying for a predetermined time, and then sintering. Next, an Ag paste is applied by screen printing from the carbon electrode 5 to the CdS film 3 and the transparent conductive film 2 of the adjacent cell, dried, and dried.
An n-electrode 6 is formed. Thereby, a plurality of solar cells are formed on the same light-transmitting substrate, and a solar cell submodule in which these are connected in series is configured. Note that a single solar cell with electrodes can be formed on a light-transmitting substrate by a method according to the above. Here, the solar cell with the electrodes is referred to as a solar cell submodule.

The transparent conductive film 2 has high light transmittance.
And low resistance (preferably 20Ω / □ or less)
Preferably, for example, In_TwoO_Three, In_TwoO_Three・ SnO_Two(IT
O), SnO doped with fluorine_Two(FTO), Sb
Doped SnO_Two, In, Al, B, F, Ga or
Is ZnO doped with Si, CdIn_TwoO_Four, CdSnO
_Four, CdO, Cd_TwoSnO_Two, Zn_TwoSnO_FourAnd In_TwoO
_Three-A film of ZnO or the like can be used.

Among the above, In ₂ O ₃ , In ₂ O ₃ .Sn
O ₂ , fluorine or antimony doped SnO ₂ , I
ZnO, CdIn ₂ O ₄ doped with n, Al or Si
It is preferable to use at least one selected from the group consisting of CdSnO ₄ and CdSnO ₄ . These transparent conductive films can be formed by, for example, an electrolytic method, a sputtering method, a solution growth method, a chemical vapor deposition method, an organometallic compound pyrolysis method, an evaporation method, a spray method, a coating sintering method, or the like.

As the n-type semiconductor layer, in addition to the CdS film 3, zinc sulfide (ZnS), cadmium oxide (CdO),
A film such as zinc oxide (ZnO) can be used. C
Because the dS film has a wide band gap,
It is preferably used as an n-type semiconductor layer, for example, using a coating sintering method, an electrolytic method, a sputtering method, a solution growth method, a chemical vapor deposition method, an organometallic compound pyrolysis method, a vapor deposition method, a proximity sublimation method or a spray method. Can be formed.

The p-type semiconductor layer is not particularly limited as long as it forms a pn junction with the CdS film. In addition to the CdTe film, for example, CuInSe ₂ , Cu (InGa) (S
eS) or other films can be used. These membranes
For example, coating sintering, electrolysis, sputtering, solution growth,
It can be formed by a chemical vapor deposition method, an organometallic compound thermal decomposition method, an evaporation method, a proximity sublimation method, a spray method, or the like.

After the solar cell sub-module is constructed as described above, in the process until the solar cell module is completed using this sub-module, the solar cell sub-module is irradiated with light. The provision of this light irradiation step is the greatest feature of the present invention, and the irradiation light needs to be light that is stronger than sunlight. The specific illuminance of the irradiation light is preferably 100,000 lux or more, and more preferably 150,000 lux or more. When the illuminance of the irradiation light is 100,000 lux or more and less than 150,000 lux, the effect of reducing the contact resistance between different kinds of semiconductor layers and the resistance in the surface direction of the semiconductor layer is not always sufficient, and the effect of reducing the contact resistance is not less than 150,000 lux. By irradiating light, the conversion efficiency of the solar cell can be significantly improved. If the illuminance of the irradiation light is too high, the solar cell sub-module is overheated and the semiconductor layers and the electrodes are stressed, which may adversely affect the characteristics of the solar cell. Therefore, the upper limit of the illuminance of the irradiation light is preferably set to 400,000 lux.

In order to sufficiently obtain the effects of the present invention, the light irradiation time in the above step is preferably 1500 hours or more. In addition, since the effect of light irradiation becomes substantially constant when the time exceeds 2,000 hours, the light irradiation exceeding 2,000 hours is not necessarily required. Light irradiation time 150
If the time is less than 0 hour, the effect of improving the conversion efficiency of the solar cell cannot always be sufficiently obtained.

The wavelength of the light to be irradiated in the above step is preferably a specific wavelength of 500 to 900 nm. Semiconductor materials having high sensitivity in a wavelength range similar to the solar spectrum are basically used for solar cells. Therefore, it is generally appropriate to set the wavelength range of the irradiation light to a wavelength range similar to sunlight. In the present invention, as a result of a specific experiment with the above general theory in mind, as a result of not irradiating the reflected light on the surface of the solar cell and transmitting the light through the solar cell, the effect of the present invention can be maximized. Was found to have an optimal wavelength range of 500 to 900 nm. Most of the short-wavelength light having a wavelength of less than 500 nm is reflected on the surface of the solar cell, and most of the long-wavelength light having a wavelength exceeding 900 nm is transmitted through the solar cell. Therefore, the great effect of the present invention was not obtained.

The type of the light source of the irradiation light is 500 to 9
A sodium lamp, a xenon lamp, a metal halide lamp, a halogen lamp, a mercury lamp, or the like having a peak in a wavelength range of 00 nm can be used. Among them, the sodium lamp is a particularly preferable light source because it emits light having a wavelength close to the sunlight spectrum, has the highest luminous efficiency, and can stably emit light with high illuminance.

According to the present invention, a solar cell which can be expected to have a particularly large effect of improving the performance is a CdS / CdTe as described above.
Various polycrystalline compound semiconductor solar cells such as solar cells and CIS solar cells. In particular, the CdTe layer tends to increase the resistance in the plane direction due to the electrical barrier at the grain boundary, so that a remarkable effect is obtained when the present invention is applied to various solar cells having the CdTe layer as a p-type semiconductor layer.

[0024]

Next, the present invention will be described with reference to specific examples.

Example 1 In this example, a solar cell having the structure shown in FIG. 1 was manufactured. First, a 400 nm-thick fluorine-doped SnO ₂ film was formed as a transparent conductive film 2 on a glass substrate 1 having a size of 10 cm × 10 cm by an evaporation method. Next, in order to form a CdS film 3 on the transparent conductive film 2, a paste obtained by screen-printing a paste obtained by kneading cadmium diethyldithiocarbamate and propylene glycol as a source material is produced, and a gap is formed between the source substrate and the gap. The CdS film 3 was formed by facing the glass substrate 1 on which the transparent conductive film 2 had been formed and thermally decomposing the source material.

Next, the transparent conductive film 2 and the CdS film 3 are scribed at the same time to divide the film into single cell units.
The e-film 4 was formed as follows. First, a source substrate was prepared by screen-printing a paste-like mixture obtained by kneading CdTe powder and phenyl glycol, and a divided transparent conductive film 2 and CdS film 3 were formed facing the source substrate. The glass substrate 1 is set, and the source substrate is heated at 640 ° C. under a reduced pressure of 1 torr.
Was heated to 600 ° C. and held for 2 minutes, whereby a CdTe film 4 having a thickness of 5 μm was formed on the glass substrate 1 on which the divided transparent conductive film 2 and CdS film 3 were formed. Thereafter, an aqueous solution of CdCl ₂ was applied onto the CdTe film 4 by a spray method, and was heated at 430 ° C. for 30 minutes in a nitrogen atmosphere containing 1% oxygen in a belt type electric furnace, and then washed with water.

Next, the CdTe film 4 was scribed and divided into single-cell-unit films, and a carbon electrode 5 was formed on the CdTe film 4. Further, an AgIn electrode 6 was formed from the carbon electrode 5 to the CdS film 3 and the transparent conductive film 2 of the adjacent cell, and a solar cell submodule in which each cell was connected in series was manufactured.

Next, the solar cell submodule obtained as described above was irradiated with light at room temperature under various conditions of varying illuminance and irradiation time. Light irradiation was performed from the light receiving surface side of the solar cell submodule, and a sodium lamp was used as a light source. The measurement of the photoelectric characteristics of each solar cell sub-module was performed using a solar simulator at 25 ° C. and A
M1.5 was performed under the conditions of 100 mW / cm ² .

FIG. 2 shows the relationship between the light irradiation time and the conversion efficiency of the solar cell module when the illuminance is a constant value of 250,000 lux. From FIG. 2, it can be seen that when the light irradiation time is shorter than 1500 hours, the conversion efficiency is slightly improved with time, but no remarkable effect is observed. However, the conversion efficiency improving effect is remarkably increased from the light irradiation time of 1500 hours to 2000 hours, and the light irradiation time is 20 hours.
When the time exceeds 00 hours, no further effect is observed and a certain conversion efficiency is shown.

Next, various output characteristics of each of the solar cell sub-modules before the light irradiation and after the light irradiation for 2,000 hours were measured, and the results are shown in Table 1.

[0031]

[Table 1]

From Table 1, it can be seen that the characteristic of which improvement was particularly observed by light irradiation is a fill factor. This is because the electric barrier at the crystal grain boundaries of the CdTe layer and the removal of crystal defects in the layer by light irradiation sufficiently reduced the ohmic contact resistance between the resistance component in the plane direction of the CdTe layer and the carbon electrode. Is considered to be the main factor.

Table 2 shows the conversion efficiency of the solar cell module after light irradiation when the light irradiation time was set to a constant value of 2000 hours and the illuminance was changed.

[0034]

[Table 2]

As can be seen from Table 2, when light having an illuminance of 100,000 lux or 130,000 lux is irradiated, the conversion efficiency is slightly improved as compared to before the light irradiation, but no significant effect is observed. Was. However, as the illuminance of the irradiation light increased to 150,000 lux, 200,000 lux, and 250,000 lux, the effect of improving the conversion efficiency was remarkably recognized.

Next, light irradiation was performed for 2000 hours at a constant illuminance of 250,000 lux using various lamps as light sources. As the light source, a lamp which emits light of a wavelength of 500 to 900 nm at all was selected. Table 3 shows the conversion efficiency of the solar cell module before and after light irradiation.

[0037]

[Table 3]

From Table 3, it can be seen that the conversion efficiency is particularly remarkably improved when the sodium lamp is used as compared with the case where other lamps are used, which is due to the improvement of the fill factor and the short-circuit current. is there. The light of a xenon lamp or a metal halide lamp has a well-balanced spectrum in the visible region, while the light of a sodium lamp has a strong peak wavelength in the visible region between 550 nm and 650 nm, which is close to the peak value of the solar spectrum. Because it has, it is effectively absorbed by the solar cell module. For this reason, it is considered that the effect of reducing the ohmic contact resistance between the resistance component in the surface direction and the carbon electrode is particularly large when a sodium lamp is used.

[0039]

According to the present invention, it is possible to reduce the contact resistance between different kinds of material films by removing crystal defects in the semiconductor layer constituting the solar cell. Further, in a polycrystalline compound semiconductor solar cell, an effect of reducing the resistance component in the plane direction of the semiconductor layer is added. As a result, the conversion efficiency of solar cells, particularly various polycrystalline compound semiconductor solar cells such as CdS / CdTe solar cells, can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a solar cell submodule according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a light irradiation time and a conversion efficiency of a solar cell submodule according to an example of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 translucent substrate 2 transparent conductive film 3 CdS film 4 CdTe film 5 carbon electrode 6 AgIn electrode

Claims (6)

[Claims] An n-type semiconductor layer and a p-type semiconductor layer are formed by laminating the sub-module, and an electrode electrically connected to each of the n-type semiconductor layer and the p-type semiconductor layer is formed. 10 from the light receiving surface side of the submodule
A method for manufacturing a solar cell, comprising a step of irradiating light having an illuminance of 10,000 lux or more. 2. The method for manufacturing a solar cell according to claim 1, wherein the illuminance of the irradiated light is 150,000 lux or more. 3. The method according to claim 2, wherein the irradiation time of the irradiation light is 1500 hours or more. 4. The wavelength range of the irradiating light is 500-9.
The method for producing a solar cell according to claim 2, wherein the thickness is 00 nm. 5. The method for manufacturing a solar cell according to claim 1, wherein a light source of the irradiating light is a sodium lamp. 6. The method for manufacturing a solar cell according to claim 1, wherein said solar cell is a polycrystalline compound semiconductor solar cell.