JP3720456B2 - Photovoltaic element - Google Patents

Description

【ミドルセル】

【トップセル】

【００２９】
【発明の効果】
本発明によりアルミニウム特有の８３０ｎｍ近傍の反射率の低下が改善され、また耐マイグレーションに優れた特性を失わない裏面反射層が得られる。その結果高信頼性かつ高変換効率の光起電力素子を得ることができる。また、本発明の裏面反射層の主材料となるアルミニウムは安価であるため、低コストでの量産も可能となる。
【図面の簡単な説明】
【図１】本発明の光起電力素子の構成の一例の略断面図である。
【図２】Ａｇ，Ａｌ，Ｃｕ，Ｎｉ膜の反射率を示す。
【図３】テクスチャー構造の裏面反射層を用いたことによる入射光の吸収の増加の例を示す。
【図４】ＤＣマグネトロンスパッタ装置の構成を示す。
【図５】実験１において得られた反射率の測定結果を示す図である。
【図６】実験１において得られたＸ線回折測定の結果を示す図である。
【図７】実験３において得られた反射率の測定結果を示す図である。
【図８】実験２において得られた反射率の測定結果を示す図である。
【図９】実験４において得られた反射率の測定結果を示す図である。
【図１０】実験６において得られたＲｓｈＤｋの変化の測定結果を示す図である。
【図１１】容量結合型高周波ＣＶＤ装置の構成を示す図である。
【図１２】連続成膜装置の構成を示す図である。
【図１３】ロール・ツー・ロール方式の光起電力素子形成装置の構成を示す図である。
【図１４】本発明のタンデム太陽電池の構成の一例の略断面図である。
【符号の説明】
１０１，１２０１ 基板
１０２，１２０２ 金属層
１０３ 透明層
１０４ 半導体層
１０５，１２０６，１２１０ ｎ型ａ−Ｓｉ層
１０６，１２１１ ｉ型ａ−Ｓｉ層
１０７ ｐ型ａ−Ｓｉ層
１０８，１２１３ 透明電極
１０９，１２１４ 集電電極
１２０３ Ａｌ−Ａｇ合金層
１２０４ ＺｎＯ層
１２０５ ボトムセル
１２０７ ｉ型ａ−ＳｉＧｅ層
１２０８，１２１２ ｐ型μｃ−Ｓｉ層
１２０９ トップセル[0001]
[Industrial application fields]
The present invention relates to a photovoltaic element having a high conversion efficiency and high reliability, using a reflective layer in which a drop in reflectance near 800 nm, which is peculiar to aluminum, is improved.
[0002]
[Prior art]
As an energy source, oil and coal, which are said to cause global warming due to carbon dioxide generated as a result of their use, nuclear power that is not at risk of radiation even in unexpected operation or even during normal operation There are many problems with being totally dependent.
[0003]
By the way, since the solar cell uses sunlight as an energy source and has very little influence on the global environment, further spread is expected. At present, however, there are several problems that prevent full-scale penetration.
Conventionally, monocrystalline or polycrystalline silicon has been often used for photovoltaic power generation. However, these solar cells require a lot of energy and time for crystal growth, and since complicated processes are required thereafter, it is difficult to increase the mass production effect, and it is therefore difficult to provide them at a low price. On the other hand, amorphous silicon (hereinafter referred to as a-Si), CdS · CuInSe ₂ So-called thin film semiconductor solar cells using compound semiconductors such as these have been actively researched and developed. In these solar cells, it is only necessary to form as many semiconductor layers as necessary on an inexpensive substrate such as glass or stainless steel, the manufacturing process is relatively simple, and the cost can be reduced. However, thin-film solar cells are not used in earnest at present because their conversion efficiency is lower than that of crystalline silicon solar cells and there is concern about reliability for long-term use. For these reasons, various attempts have been made to improve the performance of thin film solar cells.
[0004]
One of them is a back reflection layer for increasing the reflectance of light on the surface of the substrate, so that sunlight that has not been absorbed by the thin film semiconductor layer is returned to the thin film semiconductor layer and the incident light is effectively used. . Since the short wavelength component in the sunlight spectrum is already absorbed by the thin film semiconductor, it is sufficient that the reflectance is higher for light having a longer wavelength. The wavelength above which the reflectance should be high depends on the light absorption coefficient and film thickness of the thin film semiconductor to be used. When sunlight is incident from the substrate side of a transparent substrate, an electrode formed on the surface of the thin film semiconductor is preferably formed using a metal having high reflectance such as silver (Ag) or copper (Cu). Here, in order to compare the reflectivity of various metals, the reflectivity of an Ag, Al, Cu, Ni film deposited in 2000 mm is shown in FIG. When sunlight is incident from the surface of the thin film semiconductor layer, a semiconductor layer is preferably formed after a similar metal layer is formed over the substrate. Further, when a transparent layer having appropriate optical properties is interposed between the metal layer and the thin film semiconductor layer, the reflectance can be further increased by the multiple interference effect. The use of such a transparent layer is also effective in increasing the reliability of the thin film solar cell. Japanese Examined Patent Publication No. 60-41878 discloses that the use of a transparent layer can prevent the semiconductor and metal layers from being alloyed. Further, in US Pat. Nos. 4,532,372 and 4,598,306, an electrode is used even if a short circuit occurs in the semiconductor layer by using a transparent layer having an appropriate resistance. There is a description that it is possible to prevent an excessive current from flowing between them.
[0005]
Further, as another device for improving the conversion efficiency of the thin film solar cell, there is a method in which the surface of the solar cell or / and the interface with the back surface reflection layer is made into a fine uneven structure (texture structure). By adopting such a configuration, sunlight is scattered at the front surface of the solar cell or / and the interface with the back surface reflection layer, and further confined inside the semiconductor (light trap effect) so that it can be effectively absorbed in the semiconductor. become. If the substrate is transparent, tin oxide (SnO) on the substrate ₂ The surface of the transparent electrode such as) should have a textured structure. In addition, when sunlight is incident from the surface of the thin film semiconductor, the surface of the metal layer used for the back reflective layer may have a texture structure. M.M. Have reported that a texture structure for the back reflective layer can be obtained by depositing Al by adjusting the substrate temperature and deposition rate (Solar Energy Materials 20 (1990) pp99-110). FIG. 3 shows an example of the increase in absorption of incident light due to the use of the back surface reflection layer having such a texture structure. Here, curve (a) shows the spectral sensitivity of an a-SiGe solar cell using smooth silver as the metal layer, and curve (b) shows the spectral sensitivity when textured silver is used. From FIG. 3, light in the vicinity of the wavelength of 800 nm is not effectively used in the a-SiGe semiconductor layer. Therefore, in order to further increase the conversion efficiency, a back reflection layer having a high reflectance with respect to light in the vicinity of 800 nm is used. It is understood that it is good. Here, looking again at FIG. 2, silver and copper show high reflectivity in the entire wavelength region of 700 to 1000 nm required for a thin film semiconductor, whereas aluminum has a minimum value in the vicinity of a wavelength of 800 nm. Therefore, it can be said that silver and copper exhibiting a high reflectance at 800 nm are metals having a reflectance most suitable for the metal layer.
Furthermore, it is possible to combine the concept of a back surface reflection layer composed of two layers of a metal layer and a transparent layer with the concept of a texture structure. U.S. Pat. No. 4,419,533 discloses the concept of a back reflecting layer in which the surface of a metal layer has a texture structure and a transparent layer is formed thereon. It is also possible to form a transparent layer having a texture structure on a smooth metal layer. Such a combination is expected to significantly improve the conversion efficiency of the solar cell.
[0006]
[Problems to be solved by the invention]
The use of silver or copper having excellent reflectance as the metal for the back reflective layer is extremely advantageous for obtaining a solar cell with high conversion efficiency. However, these metals, particularly silver, are known as metals that cause electrochemical migration.
Electrochemical migration (hereinafter referred to as migration) is a state in which a metal such as foil, plating or paste is in contact with a highly hygroscopic or highly hydrophilic insulator under a condition where a DC voltage is applied, and When used in a high-humidity environment, it is a phenomenon in which the surface or interior of an insulator grows in a dendritic or stain-like manner by electrolysis and creates a conductive path. Depending on the metal, other conditions are required. For example, when migration is experimentally generated, silver (Ag), copper (Cu), lead (Pb), etc. are generated under conditions of distilled water and an electric field (Ag has a particularly fast growth rate of dendritic crystals) Gold (Au), palladium (Pd), indium (In), etc. need to further have halogen ions, and aluminum (Al), nickel (Ni), iron (Fe), etc. must be under special conditions other than these. It is known not to occur.
[0007]
For solar cells that can be used in various environments, short-circuiting between electrodes due to migration becomes a problem during long-term use. For example, consider a case where a solar cell actually used outdoors is exposed to a hot and humid environment. In general, since a single solar cell has a low output voltage, a plurality of submodules (a module obtained by modularizing the above-described thin film semiconductor solar cells) are connected in series. When such a solar cell is partially covered by fallen leaves or the like, the output current of the submodule in the covered portion becomes extremely smaller than other submodules, and the internal impedance is substantially increased. As a result, the output voltage of the other submodule is reversed. That is, the migration occurrence condition of applying high temperature and high humidity and reverse bias is realized, and a short circuit between the electrodes occurs, resulting in destruction of the submodule. This is especially true when Ag or Cu having a high reflectance is used for the back surface reflection layer. On the other hand, Al, which is excellent in migration resistance, has a wavelength region with low reflectivity in the vicinity of 830 nm. Therefore, if it is used as a reflective layer, high conversion efficiency equivalent to Ag or Cu cannot be expected.
[0008]
[Means for Solving the Problems]
The present invention has been made in view of the current situation, and aims to provide a photovoltaic device with high conversion efficiency at a low price by improving the decrease in reflectance of Al with respect to wavelengths near 800 nm. To do.
An object of the present invention is to provide a photovoltaic element in which at least a reflective layer, a transparent layer, a semiconductor layer, and a transparent electrode are formed on a substrate. Al-Ti alloy with Ti concentration of 5 atomic% or less or Al-Mg alloy with Mg concentration of 5 atomic% or less The (111) peak intensity in the X-ray diffraction pattern appears strongly over 2.1 times the (200) peak, 4.4 times the (220), and 4.1 times the (311) peak. Is achieved.
[0009]
[Operation and embodiment examples]
Hereinafter, the contents of the present invention will be described in detail while explaining experiments conducted by the present inventors in the process of completing the present invention.
An example of the configuration of the photovoltaic element of the present invention is shown in FIG. In FIG. 1, reference numeral 101 denotes a substrate, and the substrate 101 is preferably a conductive metal substrate. When a non-conductive substrate is used, a metal layer may be deposited by vacuum evaporation or sputtering. 102 is a metal layer mainly composed of Al, 103 is a transparent layer, and these are collectively referred to as a back reflecting layer. The transparent layer 103 is transparent to sunlight that has passed through the semiconductor layer. It has moderate electrical resistance and its surface has a textured structure. Reference numeral 104 denotes a thin film semiconductor junction. Although FIG. 1 shows an example in which a pin-type a-Si photovoltaic device is used as a thin film semiconductor junction, a tandem cell or triple cell structure in which a plurality of pin-type a-Si-based semiconductor devices are stacked is shown. Also good. Here, 105 is n-type a-Si, 106 is i-type a-Si, and 107 is p-type a-Si. When the thin film semiconductor junction is thin, the entire thin film semiconductor often exhibits a texture structure similar to that of the transparent layer 103 as shown in FIG. A transparent electrode 108 and a current collecting electrode 109 are provided thereon.
[0010]
The metal layer 102 in the photovoltaic device of the present invention is made of a metal containing aluminum as a main component, and the (111) peak intensity of the X-ray diffraction pattern is 2.1 times the (200) peak and 4. (220). It is characterized in that it appears strongly four times and 4.1 times the (311) peak. By using such a metal layer, the following effects are brought about.
(1) By giving the film a (111) plane dominant orientation, the drop in reflectance at a wavelength of 800 nm, which is peculiar to Al, is improved, and the incident sunlight can be used effectively, and the conversion efficiency of the solar cell is improved. To do.
(2) Since the main component is Al which does not cause migration, it is excellent in migration resistance, can prevent a short circuit occurring inside a solar cell used in a harsh environment, and improves reliability.
(3) Since aluminum, which is an inexpensive metal, is the main material, mass production at low cost is possible.
[0011]
Hereinafter, experiments conducted by the present inventors will be described.
In the following experiments, a DC magnetron sputtering apparatus shown in FIG. 4 was used for forming the metal layer. In FIG. 4, 401 is a deposition chamber and can be evacuated by an unillustrated exhaust pump. A predetermined flow rate of an inert gas such as argon (Ar) is introduced into this by a gas introduction pipe 402 connected to a gas cylinder (not shown), the opening degree of the exhaust valve 403 is adjusted, and the inside of the deposition chamber 401 is predetermined. It becomes pressure. The substrate 404 is fixed to the surface of an anode 406 provided with a heater 405 therein. Opposite to the anode 306, a cathode electrode 408 having a target 407 fixed thereon is provided. The target 407 is usually a block of metal to be deposited having a purity of about 99.9 to 99.999%. The cathode electrode 408 is connected to a DC power source 409, and a DC high voltage is applied by the power source 409 to generate a plasma 410 between the anode and the cathode. The metal atoms of the target 407 are deposited on the substrate 404 by the action of the plasma. Further, the deposition rate can be further increased by using a magnetron sputtering apparatus in which a magnet is provided inside the cathode 408 and the intensity of plasma is increased.
[0012]
[Experiment 1]
On a 5cm x 5cm mirror-polished 7059 glass plate made by Corning, an Al-Ti alloy with a Ti concentration of 0.5, 2, 3, 4, 10 atomic% was deposited to a thickness of 7500 mm by DC magnetron sputtering. Samples 1a, 1b, 1c, 1d, and 1e were used. For comparison, a pure Al film was prepared in the same manner as sample 1f. Since these samples were deposited on a smooth substrate at 40 Å / sec at room temperature, the surface was smooth. The sample 1f was produced using a 99.999% Al target. Alloy samples 1a to 1e were prepared by arranging 99.999% Ti chips having a size of 5 mm × 5 mm × 1 mm on an Al target so as to obtain a desired composition. All other samples except Sample 1f were analyzed with an X-ray energy dispersive analyzer (XMA) to confirm the composition.
The reflectance with respect to light with a wavelength of 400 to 1200 nm was measured for these six types of samples. Since the reflectance of Al has a minimum value at 830 nm, the value at 830 nm is shown in FIG. 5 as a representative value of the reflectance obtained in each composition. It can be seen that the reflectance of Al at 830 nm is improved by adding a small amount of Ti, and has a maximum value at a Ti concentration of 2 atomic%. This is considered to be because the crystal structure or crystal orientation was changed due to the presence of a small amount of additive, and X-ray diffraction measurement was performed on the pure Al sample 1f and the sample 1b film having a Ti concentration of 2 atomic% with the most improved reflectance. Here, an X-ray diffraction diagram of the powder Al sample is shown in FIG. When all crystal planes exist uniformly in an aluminum film having a face-centered cubic crystal structure, the intensity ratio shown in the figure, that is, the (111) peak intensity is (200) at the angle 2θ in the figure. A diffractogram which is about 2.1 times the peak, about 4.4 times (220) and about 4.1 times the (311) peak is obtained. That is, when the peak of a certain surface appears stronger than the above-mentioned intensity ratio, it can be said that the orientation of the surface is dominant. In the case of the diffraction pattern of the sample 1f, when (111) is observed with an intensity of about 0.9 times (200) and about 0.86 times (220), the (111) plane is predominantly arranged. I can't say that. On the other hand, in the sample 1b, the (111) peak appeared as strong as about 4 times the (200) peak, and the (220) and (311) peaks were not observed. Moreover, since the peak position appearing in the diffraction diagram of the sample 1b coincided with FIG. 6, it can be determined that there is no change in the crystal structure. That is, the sample 1b is considered to have a predominantly (111) plane orientation.
[0013]
[Experiment 2]
Except for using Mg instead of Ti, the same procedure as in Experiment 1 was carried out, and an Al—Mg alloy with an Mg concentration of 0.5, 1, 5, 8, and 10 atomic% was deposited to a thickness of 7500 mm, and each was sampled. 2a, 2b, 2c, 2d, 2e. With respect to these samples, the reflectance with respect to light having a wavelength of 400 to 1200 nm was measured, and a value at 830 nm is shown in FIG. 8 as a representative value of the reflectance obtained in each composition. As in the case of adding Ti to Al, it is understood that the reflectance in the vicinity of 800 nm is improved by adding Mg in the range of 5 atomic% or less. Further, when X-ray diffraction was measured for the sample 2b, no change was observed in the crystal structure, and the (111) peak appeared at an intensity about 3.6 times the (200) peak, and the (220) and (311) peaks. Hardly appeared, and a dominant orientation of the (111) plane was observed.
[0014]
[Experiment 3]
Except that Ag was used in place of Ti, an Al—Ag alloy with an Ag concentration of 0, 3, 8, 12, 20, and 28 atomic% was deposited to a thickness of 7500 mm in the same manner as in Experiment 1, and each sample was It was set as 3a, 3b, 3c, 3d, 3e. For comparison, a pure Ag film was prepared in the same manner as sample 3f. With respect to these six types of samples, the reflectance with respect to light having a wavelength of 400 to 1200 nm was measured, and values at 830 nm are shown in FIG. 7 as representative values of the reflectance obtained in the respective compositions. Similar to the Al-Ti film, the reflectance at 830 nm is improved by adding a trace amount of Ag, and the Al-Ag film has a maximum value near the Ag concentration of 10 atomic%. The appropriate amount of Al added is 25 atomic% or less. X-ray diffraction patterns were also measured for the sample 3d film having an Ag concentration of 12 atomic%. It can be seen that only one similar strong (111) peak appears at the same 2θ position as the (111) peak of sample 1b, and the (111) plane is predominantly oriented.
[0015]
[Experiment 4]
In the same manner as in Experiment 1 except that Au was used instead of Ti, an Al—Au alloy with an Au concentration of 1, 2, 4, and 7 atomic% was deposited to a thickness of 7500 mm, and each of the samples 4a, 4b, 4c and 4d. The reflectivities of these four types of samples with respect to light having a wavelength of 400 to 1200 nm are measured, and the values at 830 nm are shown in FIG. 9 as representative values of the reflectivities obtained in the respective compositions. In the case of an Al—Au film, the reflectance at 830 nm was not improved much even when Au was added. Further, when an X-ray diffraction pattern was measured for the sample 4c film having an Au concentration of 4 atomic%, the (111) peak appeared at twice the intensity of the (220) peak, and the orientation of the (111) plane could not be confirmed.
From the above experiment, it is considered that the reflectance near 800 nm is improved when the metal containing Al as a main component is predominately oriented in the (111) plane. It is considered that an Al (111) -oriented film can be easily realized by adding an appropriate amount of an appropriate material such as Ti, Ag, Mg, etc., compared to the case of Al alone.
[0016]
[Experiment 5]
As in Experiment 1, after depositing a metal layer of Al-Ti 2 atomic%, Al-Ag 12 atomic%, and Al-Mg 1 atomic% on a 5 cm x 5 cm size stainless steel plate, ZnO was formed as a transparent layer with a film thickness of 10,000 mm. Formed. Furthermore, by glow discharge decomposition method, SiH _Four , PH _Three As a source gas, an n-type a-Si layer is 200 liters, SiH _Four I-type a-Si layer is 4000Å, SiH _Four , BF _Three , H ₂ A p-type microcrystalline (μc) Si layer was deposited as a raw material gas to form a thin film semiconductor junction. A 650 mm indium tin oxide film (ITO film) was deposited thereon as a transparent electrode by resistance heating vapor deposition, and a current collecting electrode having a width of 300 microns was formed with Ag paste to form a solar battery cell. The samples thus obtained were designated as samples 5a, 5b and 5c. Similarly, samples 5d and 5e using pure Al and pure Ag as metal layers were obtained for comparison. For these samples, the photocurrent Jsc was measured under an AM-1.5 solar simulator. Sample 5d is 16.7 mA / cm ² Sample 5e was 17.8 mA / cm ² Sample 5a was 17.2 mA / cm ² Sample 5b is 17.4 mA / cm ² Sample 5c is 17.1 mA / cm ² As a result, a high current value approaching that of a solar battery cell made of an Ag metal layer was obtained.
[0017]
[Experiment 6]
For the reliability test, the five samples obtained in Experiment 5 were applied with a reverse voltage of 0.85 V (high humidity reverse bias test) at 85% humidity and an ambient temperature of 85 ° C. in the absence of light. A change in RshDk (Rsh in a state where no light was applied) was measured for comparative evaluation. The results are shown in FIG. RshDk is 10 Ωcm ² If it falls below, an open circuit voltage will not come out under low illumination light, and the characteristic and reliability as a solar cell will appear. Therefore, in the high humidity reverse bias test, RshDk ≧ 10 kΩcm. ² Was a criterion for passing the high humidity reverse bias test. As for the sample 5e, RshDk sharply decreased at the same time as the measurement was started, and 10 kΩcm ² Has broken. Sample 5d is 31 kΩcm ² There was no further decline. Similarly, no decrease in RshDk was observed in Samples 5a, 5b, and 5c.
[0018]
Below, the back surface reflection layer used in the thin film semiconductor solar cell of this invention is demonstrated in detail.
[0019]
[Substrate and metal layer]
Various metals can be used as the substrate. Of these, stainless steel plates, galvanized steel plates, aluminum plates, copper plates and the like are suitable because of their relatively low prices. These metal plates may be used after being cut into a fixed shape, or may be used in the form of a long sheet depending on the plate thickness. In the latter case, since it can be wound in a coil shape, it is suitable for continuous production and can be easily stored and transported. Depending on the application, a crystal substrate such as silicon, a plate of glass or ceramics may be used. The surface of the substrate may be polished, but may be used as it is when the finish is good, for example, a bright annealed stainless steel substrate.
As described above, a sputtering method, which is an example of a film forming method, can be used for depositing the metal layer of the present invention. In addition, the metal layer can be deposited by resistance heating, vacuum evaporation using an electron beam, sputtering, ion plating, CVD, or the like.
[0020]
[Transparent layer and its texture structure]
Transparent layers include ZnO and In ₂ O _Three , SnO ₂ , CdO, CdSnO _Four , TiO and other oxides are often used (however, the composition ratios of the compounds shown here do not necessarily match the actual conditions). In general, the higher the light transmittance of the transparent layer, the better. However, the light does not need to be transparent to light in the wavelength region absorbed by the thin film semiconductor. The transparent layer should preferably have resistance in order to suppress the current due to pinholes and the like. On the other hand, the influence of the series resistance loss due to this resistance on the conversion efficiency of the solar cell must be within a negligible range. From this point of view, the unit area (1 cm ² ) Resistance range is preferably 10 ^-6 -10Ω, more preferably 10 ^-Five ~ 3Ω, most preferably 10 ^-Four ~ 1Ω. The transparent layer is preferably as thin as possible from the viewpoint of transparency, but an average film thickness of 1000 angstroms or more is necessary to obtain a surface texture structure. In addition, a film thickness larger than this may be necessary from the viewpoint of reliability.
For the deposition of the transparent layer, resistance heating, electron beam vacuum deposition, sputtering, ion plating, CVD, spray coating, or the like can be used. Also in this case, the sputtering apparatus shown in FIG. 4 can be used. However, in the oxide, there are a case where the oxide itself is used as a target and a case where a metal (Zn, Sn, etc.) target is used. In the latter case, oxygen needs to flow simultaneously with Ar in the deposition chamber (referred to as a reactive sputtering method).
[0021]
The reason why the light confinement occurs is that the metal layer has a texture structure, and thus the light is scattered by the metal layer. In addition, when the surface of the thin film semiconductor has a texture structure similar to that of the transparent layer, light is easily scattered due to the phase difference of light, and the light trapping effect is high.
In order to control the specific resistance of the transparent layer, an appropriate impurity may be added. As the transparent layer of the present invention, the resistivity as described above tends to be too low. Therefore, as the impurities, those that moderately increase the resistance by addition thereof are preferable. For example, an acceptor-type impurity (for example, Cu, SnO in ZnO) is added to a transparent layer that is an n-type semiconductor. ₂ In addition, an appropriate amount of Al, etc.) can be added to make it intrinsic and increase the resistance. Moreover, the addition of impurities often increases chemical resistance. In order to add impurities to the transparent film, desired impurities may be added to the evaporation source or the target. In particular, in the sputtering method, a small piece of material containing impurities may be placed on the target.
[0022]
【Example】
EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated in more detail, this invention is not limited to these Examples.
[0023]
[Example 1]
A pin-type a-Si photovoltaic device having the configuration shown in the schematic cross-sectional view of FIG. 1 was produced. In the same manner as in Experiment 1 except that an Al—Ti alloy was used as a target, a metal layer of 1 atomic% of Al—Ti was formed on a stainless steel plate at 700 mm. A ZnO layer 103 having a thickness of 10,000 mm was deposited on the substrate at a substrate temperature of 350 ° C. using a ZnO target. The surface of the ZnO layer has a texture structure. Then, the board | substrate 1001 in which the back surface reflection layer was formed was set to the commercially available capacitive coupling type | mold high frequency CVD apparatus (CHJ-3030 by ULVAC, Inc.) shown in FIG. The exhaust pump 1009 was used for roughing through the exhaust pipe of the reaction vessel 1004, and then a high vacuuming operation was performed. At this time, it was controlled by a temperature control mechanism so that the surface temperature of the substrate was 350 ° C. When exhaust is sufficiently performed, SiH is introduced from the gas introduction pipe. _Four 300 sccm, SiF _Four 4sccm, PH _Three / H ₂ (1% H ₂ Dilution) 55sccm, H ₂ 40 sccm was introduced, the opening degree of the throttle valve was adjusted, the internal pressure of the reaction vessel was maintained at 1 Torr, and 200 W of power was immediately supplied from the high frequency power source when the pressure was stabilized. The plasma was sustained for 5 minutes. Thereby, the n-type a-Si layer 107 was formed on the transparent layer 104. After exhausting again, this time SiH from the gas introduction pipe _Four 300 sccm, SiF _Four 4 sccm, H ₂ 40 sccm was introduced, the opening of the throttle valve was adjusted, the internal pressure of the reaction vessel was maintained at 1 Torr, and when the pressure stabilized, 150 W of electric power was immediately applied from the high frequency power source, and the plasma was maintained for 60 minutes. Thereby, the i-type a-Si layer was formed on the n-type a-Si layer 106.
[0024]
After exhausting again, this time SiH from the gas introduction pipe _Four 50sccm, BF _Three / H ₂ (1% H ₂ Dilution) 50sccm, H ₂ 500 sccm was introduced, the opening degree of the throttle valve was adjusted, the internal pressure of the reaction vessel was maintained at 1 Torr, and when the pressure was stabilized, 300 W of electric power was immediately supplied from the high frequency power source. The plasma was sustained for 2 minutes. Thereby, the p-type μc-Si layer 108 was formed on the i-type a-Si layer 107. Next, the obtained product was taken out from a high-frequency CVD apparatus, ITO was deposited by a resistance heating vacuum deposition apparatus, and then a paste containing an aqueous iron chloride solution was printed to form a desired pattern of the transparent electrode 109. Furthermore, Ag paste was screen-printed to form a collecting electrode 110 to complete a thin film semiconductor solar cell. Ten samples were prepared by this method, and Jsc measurement was performed under AM-1.5 light. As a result, a current value 6.1% higher than that of a pure Al metal layer solar cell was obtained on average. .
Further, when these 10 solar cells were subjected to the high humidity reverse bias test conducted in Experiment 5, no decrease in RshDk was observed.
[0025]
[Example 2]
The back surface reflection layer was continuously formed using the apparatus shown in FIG. Here, a stainless sheet roll 1101 having a width of 350 mm, a thickness of 0.2 mm, and a length of 500 m is set in the substrate delivery chamber 1103. From here, the stainless steel sheet 1102 is sent to the substrate winding chamber 1113 through the metal layer deposition chambers 1104 and 1107 and the transparent layer deposition chamber 1111. The sheet 1102 can be heated to a desired temperature by the substrate heaters 1105, 1108, and 1110 in the respective deposition chambers. The stainless steel sheet 1102 deposits a textured Al layer by magnetron sputtering at a substrate temperature of 400 ° C. in a deposition chamber 1004 in which an Al target 1006 having a purity of 99.99% is installed. Thereafter, an Al—Ag 15 atomic% alloy layer is deposited in an amount of 1000 μm by DC magnetron sputtering without raising the substrate temperature using an Al—Ag alloy target 1109 having a purity of 99.99% in the deposition chamber 1007. The target 1112 in the deposition chamber 1111 is ZnO with a purity of 99.99%, and a ZnO layer is continuously deposited by 10000 soot by DC magnetron sputtering.
[0026]
An a-Si / a-SiGe tandem solar cell having the structure shown in FIG. 14 was formed on the one produced by the above method. Here, 1201 is a substrate, 1202 is an Al metal layer, 1203 is an Al—Ag alloy layer, 1204 is a ZnO layer, 1205 is a bottom cell, and 1209 is a top cell. Further, 1206 and 1210 are n-type a-Si layers, 1208 and 1212 are p-type μc-Si layers, 1207 is an i-type a-SiGe layer, and 1211 is an i-type a-Si layer. These thin film semiconductor layers were continuously formed using a roll-to-roll type film forming apparatus as described in US Pat. No. 4,492,181. Reference numeral 1213 denotes a transparent electrode, which was deposited by a sputtering apparatus similar to the apparatus of FIG. Reference numeral 1214 denotes a current collecting electrode. After patterning the transparent electrode and forming the collecting electrode, the sheet 1102 was cut. In this way, all the processes were processed continuously, and the mass production effect was improved.
When 100 samples were prepared as described above and Jsc was measured under the light of AM-1.5, a current value 6% higher than that of a pure Al metal layer solar cell was obtained on average. Also in the high humidity reverse bias test, RshDk did not decrease.
[0027]
[Example 3]
A stainless steel in the same form as in Example 2 was used except that the surface was textured, and an Al—Mg 0.5 atomic% alloy metal layer and a transparent layer were deposited using the apparatus of FIG. The layers were deposited in the same manner as in Example 2 except that the deposition chamber 1104 was not used for deposition of the metal layer, and an Al—Mg alloy was used for the target 1109 installed in the 1107 deposition chamber. Then, the photovoltaic element was formed on the photovoltaic element formation conditions shown in Table 1 using the roll-to-roll photovoltaic element forming apparatus shown in FIG.
A sheet-like substrate (sheet width 35 cm) was set in a load chamber 5010 for introducing a sheet-like substrate. The sheet-like substrate was connected to the sheet take-up jig in the unload chamber 5050 through the entire deposition chamber and all the gas gates. Each deposition chamber is set to 10 with an exhaust device (not shown). ^-3 Exhaust below Torr. Hydrogen gas was supplied to each deposition chamber from the mixing devices 5024, 5034, 5044, 5054, 5064, 5074, 5084, 5094, 5104, 5114, 5124, 5134 and 5144 for forming each deposited film. Hydrogen gas was supplied to each gas gate from each gate gas supply device to each gas gate 5201, 5202, 5203, 5204, 5205, 5206, 5207, 5208, 5209, 5210, 5211, 5212, 5213, 5214. In this embodiment, the interval through which the gas gate passes through the sheet-like substrate is 1 mm, so that hydrogen gas (H ₂ ) Was flowed at 1000 sccm. The substrate was heated to the substrate temperature shown in Table 1 by the substrate heating heater of each deposition apparatus. When the substrate temperature was stabilized, the hydrogen gas supplied to each deposition chamber was switched to the source gas shown in Table 1 deposited in each deposition chamber. When the switching of the source gas was completed, the degree of vacuum of the deposition chambers shown in Table 1 was adjusted by adjusting the degree of opening and closing of the exhaust valve of each exhaust device. The conveyance of the sheet substrate was started. When the degree of vacuum was stabilized, RF power and MW power shown in Table 1 for plasma generation were supplied to each deposition chamber. As described above, a photovoltaic element in which three pin structures were stacked on the sheet-like substrate 100m was formed.
In this way, 100 samples were prepared, and Jsc was measured with an AM-1.5 solar simulator. An average value 5.8% higher than the current value obtained with a solar cell using a pure Al metal layer was obtained, and there was no problem in the high humidity reverse bias test.
[0028]
[Table 1]
Support: Stainless steel SUS430 (JIS standard) thickness 0.125mm
Substrate: SUS430 / Ag4500Å / ZnO 1 μm (texture structure)
[Bottom cell]

[Middle cell]

[Top cell]

[0029]
【The invention's effect】
According to the present invention, the lowering of the reflectance near 830 nm, which is peculiar to aluminum, is improved, and a back reflective layer that does not lose its excellent resistance to migration can be obtained. As a result, a photovoltaic device with high reliability and high conversion efficiency can be obtained. Moreover, since aluminum which is the main material of the back reflective layer of the present invention is inexpensive, mass production at low cost is possible.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an example of the configuration of a photovoltaic device of the present invention.
FIG. 2 shows reflectivity of Ag, Al, Cu, and Ni films.
FIG. 3 shows an example of an increase in absorption of incident light by using a back surface reflective layer having a texture structure.
FIG. 4 shows a configuration of a DC magnetron sputtering apparatus.
FIG. 5 is a diagram showing a measurement result of reflectance obtained in Experiment 1. FIG.
6 is a diagram showing the results of X-ray diffraction measurement obtained in Experiment 1. FIG.
7 is a diagram showing the measurement results of reflectance obtained in Experiment 3. FIG.
FIG. 8 is a diagram showing the measurement results of reflectance obtained in Experiment 2.
9 is a diagram showing the measurement results of reflectance obtained in Experiment 4. FIG.
FIG. 10 is a diagram showing measurement results of changes in RshDk obtained in Experiment 6.
FIG. 11 is a diagram showing a configuration of a capacitively coupled high-frequency CVD apparatus.
FIG. 12 is a diagram showing a configuration of a continuous film forming apparatus.
FIG. 13 is a diagram showing a configuration of a roll-to-roll photovoltaic device forming apparatus.
FIG. 14 is a schematic cross-sectional view of an example of the configuration of the tandem solar cell of the present invention.
[Explanation of symbols]
101,1201 substrate
102,1202 Metal layer
103 transparent layer
104 Semiconductor layer
105, 1206, 1210 n-type a-Si layer
106,1211 i-type a-Si layer
107 p-type a-Si layer
108,1213 Transparent electrode
109,1214 Current collecting electrode
1203 Al-Ag alloy layer
1204 ZnO layer
1205 bottom cell
1207 i-type a-SiGe layer
1208,1212 p-type μc-Si layer
1209 Top cell

Claims (1)

In a photovoltaic device in which at least a reflective layer, a transparent layer, a semiconductor layer, and a transparent electrode are formed on a substrate, the reflective layer is an Al—Ti alloy having a Ti concentration of 5 atomic% or less or an Mg concentration of 5 atomic% or less. It consists of an Al-Mg alloy , and its (111) peak intensity in the X-ray diffraction pattern exceeds 2.1 times the (200) peak, 4.4 times the (220), and 4.1 times the (311) peak. A photovoltaic device characterized by being strongly manifested.

Images