JP2010140992A - Thin-film solar battery - Google Patents
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Abstract
Description
本発明は、光電変換効率の高効率化を可能とする薄膜太陽電池に関する。 The present invention relates to a thin-film solar cell that enables high photoelectric conversion efficiency.
半導体薄膜を利用した薄膜太陽電池として、基板上に、金属電極、導電性透明膜、半導体層、導電性透明電極を順次積層した構造を有するものがある（特許文献１、２、３）。
ここで、金属電極は、裏面電極として使用されるが、薄膜太陽電池に入射した光のうち、半導体層で吸収されなかった光を反射して半導体層に戻し、入射した光を有効に光電変換する裏面反射効果を奏する働きもする。このため、銀（Aｇ）、アルミニウム（Aｌ）などの光反射率の高い金属の薄膜が、金属電極として用いられる。
Some thin-film solar cells using a semiconductor thin film have a structure in which a metal electrode, a conductive transparent film, a semiconductor layer, and a conductive transparent electrode are sequentially laminated on a substrate (Patent Documents 1, 2, and 3).
Here, the metal electrode is used as the back electrode, but among the light incident on the thin film solar cell, the light that has not been absorbed by the semiconductor layer is reflected back to the semiconductor layer, and the incident light is effectively photoelectrically converted. It also has the function of producing a back surface reflection effect. For this reason, a metal thin film having a high light reflectance such as silver (Ag) or aluminum (Al) is used as the metal electrode.
半導体層は、アモルファスシリコン（ａ−Ｓｉ）、多結晶シリコンまたは微結晶シリコンなどの半導体材料を用いて形成される。
金属電極と半導体層の間に形成された導電性透明膜について、特許文献２には、導電性透明膜は、金属電極と半導体層の熱膨張係数の相違による熱歪みを緩和して付着性を高め、かつ金属原子が半導体層へ拡散するのを防止すると述べられている。また、特許文献１には、導電性透明膜は金属電極の表面で反射した光に多重干渉効果を生じさせるため、反射する光の反射率が向上すると述べられている。
The semiconductor layer is formed using a semiconductor material such as amorphous silicon (a-Si), polycrystalline silicon, or microcrystalline silicon.
Regarding the conductive transparent film formed between the metal electrode and the semiconductor layer, Patent Document 2 discloses that the conductive transparent film has reduced adhesion due to the difference in thermal expansion coefficient between the metal electrode and the semiconductor layer. It is said to increase and prevent metal atoms from diffusing into the semiconductor layer. Further, Patent Document 1 states that since the conductive transparent film produces a multiple interference effect on the light reflected on the surface of the metal electrode, the reflectance of the reflected light is improved.
裏面反射効果を奏する金属電極について、特許文献１には、金属電極の表面に微細な凹凸を形成して、テクスチャー構造を形成することが述べられている。テクスチャー構造を形成することにより、金属電極の表面で反射する入射光が拡散反射されて、半導体層内部に閉じこめられるため、入射光を有効に光電変換することができる利点がある。
このように、金属電極の表面をテクスチャー構造とした場合、入射光を有効に光電変換することができるが、他方、つぎのような問題点を生じる。基板上に積層した金属電極と導電性透明膜の上に形成した半導体層の膜質が低下することがある。半導体層として、微結晶シリコンの薄膜を用いる場合、金属電極表面のテクスチャー構造の影響を受けて、微結晶シリコンの成長方向がランダムとなるときは、欠陥を生じて、その膜質が低下するため、変換効率が低下する。
Regarding a metal electrode having a back surface reflection effect, Patent Document 1 describes that fine irregularities are formed on the surface of the metal electrode to form a texture structure. By forming the texture structure, the incident light reflected on the surface of the metal electrode is diffusely reflected and confined in the semiconductor layer, so that there is an advantage that the incident light can be effectively photoelectrically converted.
As described above, when the surface of the metal electrode has a texture structure, incident light can be effectively photoelectrically converted, but the following problems occur. The film quality of the semiconductor layer formed on the metal electrode laminated on the substrate and the conductive transparent film may deteriorate. When a microcrystalline silicon thin film is used as the semiconductor layer, when the growth direction of the microcrystalline silicon is random due to the influence of the texture structure on the surface of the metal electrode, defects are generated and the film quality is lowered. Conversion efficiency decreases.
そこで、本発明は、金属電極表面のテクスチャー構造の影響を受けて、半導体層の膜質が低下し、変換効率が低下することを抑止する手段を提供することを課題とする。
上記課題は、基板上に少なくとも金属電極、導電性透明膜、半導体層、導電性透明電極がこの順で積層されてなる薄膜太陽電池において、前記導電性透明膜の膜厚を０．５μｍ以上に形成することにより解決される。
請求項１に記載の発明は、基板上に、少なくとも金属電極、導電性透明膜、半導体層、導電性透明電極がこの順で積層されてなる薄膜太陽電池において、前記導電性透明膜の膜厚が０．５μｍ以上であることを特徴とする薄膜太陽電池に係るものである。
In the thin film solar cell in which at least a metal electrode, a conductive transparent film, a semiconductor layer, and a conductive transparent electrode are laminated in this order on a substrate, the thickness of the conductive transparent film is 0.5 μm or more. It is solved by forming.
The invention according to claim 1 is a thin film solar cell in which at least a metal electrode, a conductive transparent film, a semiconductor layer, and a conductive transparent electrode are laminated in this order on a substrate, and the film thickness of the conductive transparent film Is a thin film solar cell characterized by being 0.5 μm or more.
請求項２に記載の発明は、前記半導体層が、微結晶シリコン、アモルファスシリコン、多結晶シリコンからなる群から選ばれてなることを特徴とする請求項１に記載の薄膜太陽電池に係るものである。
請求項１に記載の発明によれば、金属電極の上に形成する導電性透明膜の膜厚を０．５μｍ以上とすることにより、金属電極表面のテクスチャー構造の影響が減少するため、導電性透明膜の上に形成する半導体層の膜質の低下を抑止することができる。請求項２に記載の発明では、半導体層が微結晶シリコンからなる薄膜太陽電池において、導電性透明膜の膜厚を０．５μｍ以上とすることにより、金属電極表面のテクスチャー構造の影響が減少するため、導電性透明膜の上に形成する半導体層の膜質の低下を抑止することができる。また、導電性透明膜の膜厚を増すことにより、拡散反射率が向上する。
The invention according to claim 2 relates to the thin-film solar cell according to claim 1, wherein the semiconductor layer is selected from the group consisting of microcrystalline silicon, amorphous silicon, and polycrystalline silicon. is there.
According to the first aspect of the present invention, since the influence of the texture structure on the surface of the metal electrode is reduced by setting the film thickness of the conductive transparent film formed on the metal electrode to 0.5 μm or more, the conductivity is reduced. Degradation of the film quality of the semiconductor layer formed on the transparent film can be suppressed. In the invention according to claim 2, in the thin film solar cell in which the semiconductor layer is made of microcrystalline silicon, the influence of the texture structure on the surface of the metal electrode is reduced by setting the thickness of the conductive transparent film to 0.5 μm or more. Therefore, it is possible to suppress the deterioration of the film quality of the semiconductor layer formed on the conductive transparent film. Moreover, the diffuse reflectance is improved by increasing the film thickness of the conductive transparent film.
以上の請求項１ないし請求項２に記載の発明によれば、基板上に少なくとも金属電極、導電性透明膜、半導体層、導電性透明電極がこの順で積層されてなる薄膜太陽電池において、導電性透明膜の膜厚を０．５μｍ以上に形成することにより、金属電極表面のテクスチャー構造の影響が減少し、導電性透明膜の上に形成する半導体層の膜質の低下が抑止されるとともに、拡散反射率も向上するため、薄膜太陽電池の変換効率を向上することができる。 According to the invention described in claims 1 and 2, in the thin film solar cell in which at least a metal electrode, a conductive transparent film, a semiconductor layer, and a conductive transparent electrode are laminated in this order on a substrate, By forming the film thickness of the conductive transparent film to 0.5 μm or more, the influence of the texture structure of the metal electrode surface is reduced, and the deterioration of the film quality of the semiconductor layer formed on the conductive transparent film is suppressed, Since the diffuse reflectance is also improved, the conversion efficiency of the thin film solar cell can be improved.
本発明の実施例について、以下の実施例１にて説明する。 Examples of the present invention will be described in Example 1 below.
図１は、実施例１に係る薄膜太陽電池の構造を示す断面図である。基板１として、ガラス板（コーニング＃１７３７）を使用し、基板１上に、金属電極２として、０．３原子％（ａｔ％）のＡｌを含むＡｇ合金膜（膜厚２００ｎｍ）を形成した。基板１としては、ガラス基板の他に、ポリイミドのような高分子フィルムからなる可撓性基板が使用するのに適切である。さらに、導電性透明膜３として、酸化亜鉛膜（ＺｎＯ膜）を形成した。Ａｇ合金膜、ＺｎＯ膜は、いずれもマグネトロン・スパッタリング法により同一真空槽内で、製膜温度３５０℃にて連続的に形成した。Ａｇ合金膜はアルゴン雰囲気０．６７Ｐａにて、０．５６ｎｍ／秒の製膜速度で、ＺｎＯ膜はアルゴン−酸素混合ガス（ガス流量比でアルゴン９８に対し酸素２）雰囲気０．６７Ｐａにて、０．１１ｎｍ／秒の製膜速度で製膜した。 FIG. 1 is a cross-sectional view illustrating the structure of the thin-film solar cell according to the first embodiment. A glass plate (Corning # 1737) was used as the substrate 1, and an Ag alloy film (thickness: 200 nm) containing 0.3 atomic% (at%) Al was formed as the metal electrode 2 on the substrate 1. As the substrate 1, in addition to the glass substrate, a flexible substrate made of a polymer film such as polyimide is suitable. Further, a zinc oxide film (ZnO film) was formed as the conductive transparent film 3. Each of the Ag alloy film and the ZnO film was continuously formed at a film forming temperature of 350 ° C. in the same vacuum chamber by a magnetron sputtering method. The Ag alloy film has an argon atmosphere of 0.67 Pa, a film forming speed of 0.56 nm / second, and the ZnO film has an argon-oxygen mixed gas (oxygen 2 with respect to argon 98 by gas flow ratio) atmosphere of 0.67 Pa. The film was formed at a film forming speed of 0.11 nm / second.
ＺｎＯ膜については、膜厚の異なる５種類（膜厚５０ｎｍ、０．５μｍ、１μｍ、１．５μｍ、２μｍ）を作製した。膜厚５０ｎｍのＺｎＯ膜を試料ａ１とし、以下、膜厚の増す順に、試料ａ２、ａ３、ａ４、ａ５とする。また、比較試料として、製膜温度２５０℃にて作製したＺｎＯ膜（膜厚５０ｎｍ）を試料ｂとする。
ＺｎＯ膜の上に、半導体層４として、微結晶シリコン層（ｉ層の膜厚２μｍ）を形成し、さらに微結晶シリコン層の上に、導電性透明電極５としてＩＴＯ膜を形成したのち、金属櫛型電極６を形成した。
Regarding the ZnO film, five types having different film thicknesses (film thicknesses 50 nm, 0.5 μm, 1 μm, 1.5 μm, and 2 μm) were produced. A ZnO film having a thickness of 50 nm is referred to as a sample a1, and hereinafter referred to as samples a2, a3, a4, and a5 in order of increasing film thickness. Further, as a comparative sample, a ZnO film (film thickness 50 nm) manufactured at a film forming temperature of 250 ° C. is set as a sample b.
A microcrystalline silicon layer (i layer thickness 2 μm) is formed as a semiconductor layer 4 on the ZnO film, and an ITO film is formed as a conductive transparent electrode 5 on the microcrystalline silicon layer. Comb electrodes 6 were formed.
以上のように作製したＺｎＯ膜の膜厚が異なる薄膜太陽電池について、その変換効率を測定した。その結果は後述する。以上の薄膜太陽電池の試料のほかに、基板１上にＡｇ合金膜（膜厚２００ｎｍ）、ＺｎＯ膜を積層した試料を作製し、拡散反射率の測定、走査型電子顕微鏡（ＳＥＭ）による表面観察を行った。ＺｎＯ膜の製膜温度２５０℃、膜厚５０ｎｍの試料を試料ｂ、製膜温度３５０℃、膜厚５０ｎｍを試料ａ１、製膜温度３５０℃、膜厚２μｍを試料ａ５とする。 The conversion efficiency was measured about the thin film solar cell from which the film thickness of the ZnO film | membrane produced as mentioned above differs. The result will be described later. In addition to the above thin film solar cell sample, a sample in which an Ag alloy film (thickness: 200 nm) and a ZnO film is laminated on the substrate 1 is manufactured, and the diffuse reflectance is measured, and the surface is observed with a scanning electron microscope (SEM). Went. A sample having a ZnO film deposition temperature of 250 ° C. and a film thickness of 50 nm is designated as sample b, a film deposition temperature of 350 ° C. and a film thickness of 50 nm as sample a1, a film deposition temperature of 350 ° C., and a film thickness of 2 μm as sample a5.
図２は、試料ｂ、ａ１、ａ５について、波長の変化に対する拡散反射率の変化を測定した結果である。拡散反射率は正反射光だけを選択的に除去する光学測定系を用いて測定した。試料ａ５の拡散反射率は、試料ｂと比べ、４３７ｎｍ以上の波長範囲で約１５〜４０％向上している。また、試料ａ５は、試料ａ１と比べ、４２４ｎｍ未満の波長範囲では低下している。 FIG. 2 shows the results of measuring the change in diffuse reflectance with respect to the change in wavelength for samples b, a1, and a5. The diffuse reflectance was measured using an optical measurement system that selectively removes only regular reflection light. The diffuse reflectance of the sample a5 is improved by about 15 to 40% in the wavelength range of 437 nm or more compared to the sample b. In addition, the sample a5 is lower than the sample a1 in the wavelength range of less than 424 nm.
ＳＥＭによる表面構造を図３（試料ｂ）、図４（試料ａ１）、図５（試料ａ５）に示す。ＺｎＯ膜の膜厚が厚い図５の試料ａ５は、図３の試料ｂおよび図４の試料ａ１と比べ、Ａｇ合金膜に由来する凹凸構造から表面形態が変化している。
薄膜太陽電池の試料について、その量子効率を測定した結果を図６に示す。図６において、試料ａ５は、試料ｂと比べ、波長５００ｎｍ以上の長波長範囲で量子効率が向上している。また、４２４ｎｍ以下の短波長範囲では両者に違いがない。
The surface structure by SEM is shown in FIG. 3 (sample b), FIG. 4 (sample a1), and FIG. 5 (sample a5). The sample a5 of FIG. 5 having a thick ZnO film has a surface shape changed from the concavo-convex structure derived from the Ag alloy film as compared to the sample b of FIG. 3 and the sample a1 of FIG.
The result of measuring the quantum efficiency of the sample of the thin film solar cell is shown in FIG. In FIG. 6, the quantum efficiency of the sample a5 is improved in the long wavelength range of 500 nm or more compared to the sample b. Further, there is no difference between them in the short wavelength range of 424 nm or less.
薄膜太陽電池の試料について、その変換効率を測定した結果を図７に示す。ＺｎＯ膜の製膜温度３５０℃、膜厚が５０ｎｍである試料ａ１の変換効率を１として、ＺｎＯ膜の膜厚の変化に対する変換効率の変化を表している。変換効率は、ＺｎＯ膜の膜厚が０．５μｍ以上では増大し、向上している。これは、ＺｎＯ膜の膜厚が増すことによって、ＺｎＯ膜の下に形成した金属電極２のＡｇ合金膜表面のテクスチャー構造の影響が減少し、半導体層４の微結晶シリコンの膜質の低下が抑止されたことを示している。また、この変換効率の向上には、図２の拡散反射率の結果が示すように、拡散反射率の向上も寄与している。 FIG. 7 shows the results of measuring the conversion efficiency of the thin film solar cell sample. The change in conversion efficiency with respect to the change in film thickness of the ZnO film is represented by assuming that the conversion efficiency of the sample a1 having a ZnO film formation temperature of 350 ° C. and a film thickness of 50 nm is 1. The conversion efficiency is increased and improved when the thickness of the ZnO film is 0.5 μm or more. This is because the influence of the texture structure on the surface of the Ag alloy film of the metal electrode 2 formed under the ZnO film is reduced by increasing the film thickness of the ZnO film, and the deterioration of the film quality of the microcrystalline silicon of the semiconductor layer 4 is suppressed. It has been shown. Further, the improvement of the diffusion efficiency also contributes to the improvement of the conversion efficiency, as the result of the diffuse reflectance of FIG.
以上の実施例１において、半導体層４として微結晶シリコン層を用いたが、アモルファスシリコン（ａ−Ｓｉ）、または多結晶シリコンを使用した薄膜太陽電池においても、導電性透明膜３の膜厚を０．５μｍ以上に形成することにより、金属電極２表面のテクスチャー構造の影響が減少し、導電性透明膜３の上に形成する半導体層４の膜質の低下が抑止される。 In Example 1 described above, a microcrystalline silicon layer is used as the semiconductor layer 4, but the thickness of the conductive transparent film 3 is also reduced in a thin film solar cell using amorphous silicon (a-Si) or polycrystalline silicon. By forming to 0.5 μm or more, the influence of the texture structure on the surface of the metal electrode 2 is reduced, and the deterioration of the film quality of the semiconductor layer 4 formed on the conductive transparent film 3 is suppressed.
１ 基板
２ 金属電極
３ 導電性透明膜
４ 半導体層
５ 導電性透明電極
６ 金属櫛型電極
DESCRIPTION OF SYMBOLS 1 Substrate 2 Metal electrode 3 Conductive transparent film 4 Semiconductor layer 5 Conductive transparent electrode 6 Metal comb electrode
Claims (2)
The thin film solar cell according to claim 1, wherein the semiconductor layer is selected from the group consisting of microcrystalline silicon, amorphous silicon, and polycrystalline silicon.
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| JP2002222975A (en) * | 2001-01-29 | 2002-08-09 | Kyocera Corp | THIN FILM CRYSTALLINE Si SOLAR BATTERY AND ITS MANUFACTURING METHOD |
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