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JP2007059644A - Photovoltaic element - Google Patents

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JP2007059644A
JP2007059644A JP2005243752A JP2005243752A JP2007059644A JP 2007059644 A JP2007059644 A JP 2007059644A JP 2005243752 A JP2005243752 A JP 2005243752A JP 2005243752 A JP2005243752 A JP 2005243752A JP 2007059644 A JP2007059644 A JP 2007059644A
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semiconductor substrate
layer thickness
photovoltaic device
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Kenichi Okumura
健一 奥村
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Toyota Motor Corp
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Abstract

【課題】 キャリアの収集効率が最大である光起電力素子を得て、その発電効率を向上させる。
【解決手段】 半導体基板の受光面とは反対側の裏面に正および負の電極を配置した裏面電極型の光起電力素子において、半導体基板（１１）の受光面と正電極（１５）間の層厚ａを正孔の拡散定数に基づいて決定し、受光面と負電極（１４）間の層厚ｂを電子の拡散定数に基づいて決定する。これによって、正電極における正孔の収集割合と負電極における電子の収集割合が等しくなり、最大の効率でキャリアを収集することができるので、光起電力素子の発電効率が向上する。
【選択図】 図２
PROBLEM TO BE SOLVED: To obtain a photovoltaic device having the highest carrier collection efficiency and to improve the power generation efficiency.
In a back electrode type photovoltaic device in which positive and negative electrodes are arranged on the back surface opposite to the light receiving surface of a semiconductor substrate, the space between the light receiving surface of the semiconductor substrate (11) and the positive electrode (15) is provided. The layer thickness a is determined based on the hole diffusion constant, and the layer thickness b between the light receiving surface and the negative electrode (14) is determined based on the electron diffusion constant. As a result, the hole collection ratio at the positive electrode is equal to the electron collection ratio at the negative electrode, and carriers can be collected with maximum efficiency, so that the power generation efficiency of the photovoltaic device is improved.
[Selection] Figure 2

Description

本発明は、裏面電極型の光起電力素子に関し、特にその発電効率を改善した光起電力素子に関する。   The present invention relates to a back electrode type photovoltaic device, and more particularly to a photovoltaic device with improved power generation efficiency.

裏面電極型の光起電力素子（光電池、太陽電池等を含む）は、従来から周知である（例えば特許文献１〜４参照）。図１は、従来の光起電力素子の概略断面図である。光起電力素子１００を構成する半導体基板１（ｐ型またはｎ型の単結晶半導体）において光吸収が起こると正負のキャリアとしての電子および正孔が発生する。基板１の裏面側（図の下面側）には、半導体基板１で発生したキャリアを選択的に収集するためのｎ+層（電子収集部）２およびｐ+層（正孔収集部）３が不純物拡散により形成されており、これらの層によって収集されたキャリアは、基板１の下面に形成された負電極４、正電極５によって外部に出力される。なお、負電極４はｎ+層２に接して形成され、正電極５はｐ+層３と接して形成されている。この接続部以外において基板１の下面は表面保護膜（絶縁膜）６ａにより被覆されている。基板１の受光面側（図の上面側）にも同様に表面保護膜６ｂが形成され、更にその上に反射防止膜７が形成されている。 Back electrode type photovoltaic elements (including photovoltaic cells, solar cells, and the like) have been conventionally known (see, for example, Patent Documents 1 to 4). FIG. 1 is a schematic cross-sectional view of a conventional photovoltaic device. When light absorption occurs in the semiconductor substrate 1 (p-type or n-type single crystal semiconductor) constituting the photovoltaic element 100, electrons and holes as positive and negative carriers are generated. An n + layer (electron collecting unit) 2 and a p + layer (hole collecting unit) 3 for selectively collecting carriers generated in the semiconductor substrate 1 are provided on the back surface side (lower surface side in the figure) of the substrate 1. The carriers formed by impurity diffusion and collected by these layers are output to the outside by the negative electrode 4 and the positive electrode 5 formed on the lower surface of the substrate 1. The negative electrode 4 is formed in contact with the n + layer 2, and the positive electrode 5 is formed in contact with the p + layer 3. Except for this connection portion, the lower surface of the substrate 1 is covered with a surface protective film (insulating film) 6a. Similarly, a surface protective film 6b is formed on the light receiving surface side (upper surface side in the figure) of the substrate 1, and an antireflection film 7 is further formed thereon.

上記従来の光起電力素子では、半導体基板１はｎまたはｐのいずれか一方の伝導型を有し、単一のキャリア濃度で形成されているので、光吸収によって発生した電子と正孔はキャリアの収集部即ちｎ+層２とｐ+層３に到達するまでに、共に半導体基板１内を通過する。そのため、基板１内で電子と正孔が再結合して消滅する確率が高く、再結合損失により発電効率が低下するという問題があった。 In the above conventional photovoltaic device, the semiconductor substrate 1 has either n or p conductivity type and is formed with a single carrier concentration, so that electrons and holes generated by light absorption are carriers. Both of them pass through the semiconductor substrate 1 before reaching the collector, that is, the n + layer 2 and the p + layer 3. For this reason, there is a high probability that electrons and holes recombine and disappear in the substrate 1, and power generation efficiency is reduced due to recombination loss.

上記問題を解決するために、特許文献１に記載の発明では、半導体基板に、それぞれ１個の電子収集部あるいは正孔収集部を含んで基板の表面側から裏面側に延在する複数の領域を設け、隣接する領域間で導電型を異ならせ、あるいはキャリア濃度を異ならせることにより、キャリアの再結合を防止する構造をとっている（図１および図５参照）。また、同一領域内において、表面からの距離に応じてキャリア濃度に勾配を設け、さらにキャリアの再結合を防止する構造としている（図３および図７参照）。このような構造によって、光起電力素子の発電効率の向上が確認されている。   In order to solve the above problem, in the invention described in Patent Document 1, the semiconductor substrate includes a plurality of regions each including one electron collecting portion or hole collecting portion and extending from the front surface side to the back surface side of the substrate. And a structure in which recombination of carriers is prevented by changing the conductivity type between adjacent regions or by changing the carrier concentration (see FIGS. 1 and 5). Further, in the same region, a gradient is provided in the carrier concentration according to the distance from the surface, and further, carrier recombination is prevented (see FIGS. 3 and 7). Such a structure has been confirmed to improve the power generation efficiency of the photovoltaic element.

また、特許文献２に記載の光起電力素子では、半導体基板の側面、即ち切断面に基板半導体との間でショットキー障壁を形成する金属膜を設け、キャリアの捕獲中心が高濃度で形成されている半導体基板側面（即ち切断面）へのキャリアの移動を防止する構成をとっている。この構成により、キャリアの再結合損失が低下し、光起電力素子の発電効率が向上する。   In the photovoltaic device described in Patent Document 2, a metal film that forms a Schottky barrier is provided on the side surface of the semiconductor substrate, that is, the cut surface, with the substrate semiconductor, and the carrier trapping center is formed at a high concentration. The carrier is prevented from moving to the side surface (that is, the cut surface) of the semiconductor substrate. With this configuration, the carrier recombination loss is reduced, and the power generation efficiency of the photovoltaic element is improved.

また、特許文献３および４に記載の光起電力素子では、半導体基板の受光面側に不純物拡散層を設け、この拡散層と半導体基板間に形成されるエネルギー障壁によりキャリア追い返し効果を形成して、キャリアの再結合損失を低下させる技術を開示している。拡散層を還元雰囲気または不活性ガス雰囲気下で形成することにより、素子表面近傍の欠陥数が減少し、さらにキャリアの再結合損失が低下する。   Further, in the photovoltaic elements described in Patent Documents 3 and 4, an impurity diffusion layer is provided on the light receiving surface side of the semiconductor substrate, and a carrier repelling effect is formed by an energy barrier formed between the diffusion layer and the semiconductor substrate. Discloses a technique for reducing carrier recombination loss. By forming the diffusion layer in a reducing atmosphere or an inert gas atmosphere, the number of defects in the vicinity of the element surface is reduced, and the recombination loss of carriers is further reduced.

特開２００５−１２１０８号公報JP 2005-12108 A 特開平２００４−３９７５１号公報Japanese Patent Laid-Open No. 2004-39751 特開２００３−１５２２０７号公報JP 2003-152207 A 特開２００４−７１７６３号公報Japanese Patent Application Laid-Open No. 2004-71763

上記従来の光起電力素子においては、キャリアである電子と正孔を受光面とは反対側の裏面で収集するために、半導体基板の厚さは、電子または正孔の拡散長以内で形成される。これは、基板厚さが拡散長以内であれば、半導体基板において生成された電子、正孔が、基板裏面に達するまでに再結合によって消滅してしまう確率が低下するからである。ところが、上記従来の光起電力素子では、受光面から正電極および負電極までの深さ（半導体基板の層厚）は基板全体を通じて一様であり、あるいは異なっている場合でも両者の深さについて特に規定がない。   In the above conventional photovoltaic device, the thickness of the semiconductor substrate is formed within the diffusion length of electrons or holes in order to collect electrons and holes as carriers on the back surface opposite to the light receiving surface. The This is because if the substrate thickness is within the diffusion length, the probability that electrons and holes generated in the semiconductor substrate disappear due to recombination before reaching the back surface of the substrate decreases. However, in the conventional photovoltaic device described above, the depth from the light receiving surface to the positive electrode and the negative electrode (layer thickness of the semiconductor substrate) is uniform throughout the substrate, or even when they are different, There are no specific rules.

一方、電子と正孔では拡散定数が異なっており、一般的に電子の拡散定数の方が正孔の拡散定数よりも大きい。そのため、表面からそれぞれの電極までの距離を電子の拡散長に基づいて設定した場合には、その拡散長が電子に比べて短い正孔の収集割合が電子の収集割合より劣ってしまい、結果的に電子と正孔とを最大限に効率よく収集することが困難であった。   On the other hand, electrons and holes have different diffusion constants, and generally the electron diffusion constant is larger than the hole diffusion constant. Therefore, when the distance from the surface to each electrode is set based on the diffusion length of electrons, the collection rate of holes whose diffusion length is shorter than that of electrons is inferior to the collection rate of electrons. It was difficult to collect electrons and holes with maximum efficiency.

本発明は、従来の光起電力素子における上記のような欠点を解決する目的でなされたものであり、最も効率的にキャリアを収集することが可能な新規な構造の光起電力素子を提供することを課題とする。   The present invention has been made for the purpose of solving the above-described drawbacks of conventional photovoltaic devices, and provides a photovoltaic device having a novel structure capable of collecting carriers most efficiently. This is the issue.

上記課題を解決するために、第１の発明では、半導体基板の受光面とは反対側の裏面に正および負の電極を配置した裏面電極型の光起電力素子において、半導体基板の受光面と正電極間の層厚ａを正孔の拡散定数に基づいて決定し、受光面と負電極間の層厚ｂを電子の拡散定数に基づいて決定する。   In order to solve the above-mentioned problem, in the first invention, in a back electrode type photovoltaic device in which positive and negative electrodes are arranged on the back surface opposite to the light receiving surface of the semiconductor substrate, the light receiving surface of the semiconductor substrate The layer thickness a between the positive electrodes is determined based on the hole diffusion constant, and the layer thickness b between the light receiving surface and the negative electrode is determined based on the electron diffusion constant.

具体的には、層厚ａと層厚ｂが、
ａ：ｂ＝（Ｄh）1/2：（Ｄe）1/2
となるように、ａおよびｂの値を設定する。なお、Ｄhは半導体基板中の正孔の拡散定数、Ｄeは同じく電子の拡散定数を示す。 Specifically, the layer thickness a and the layer thickness b are
a: b = (D h ) 1/2 : (D e ) 1/2
The values of a and b are set so that Here, D h is the diffusion constant of holes in the semiconductor substrate, and De is the diffusion constant of electrons.

光起電力素子の光吸収層を構成する半導体基板をｐ型シリコン基板で構成した場合、上記層厚ａは８７μｍ、上記層厚ｂは１５０μｍが望ましい。また、半導体基板をｐ型ゲルマニウムとした場合、上記層厚ａは１２０μｍ、上記層厚ｂは１５０μｍが望ましい。   When the semiconductor substrate constituting the light absorption layer of the photovoltaic element is a p-type silicon substrate, the layer thickness a is desirably 87 μm and the layer thickness b is desirably 150 μm. When the semiconductor substrate is p-type germanium, the layer thickness a is desirably 120 μm and the layer thickness b is desirably 150 μm.

第１の発明にかかる光起電力素子では、光吸収層を構成する半導体基板の厚さを、基板裏面に設けた正電極部分では正孔の拡散定数に応じて、負電極部分では電子の拡散定数に応じて設定するので、正孔の収集割合と電子の収集割合が等しくなる。その結果、本光起電力素子において、最も効率的にキャリアを収集することができるので、発電効率が向上する。   In the photovoltaic device according to the first invention, the thickness of the semiconductor substrate constituting the light absorption layer is determined according to the hole diffusion constant in the positive electrode portion provided on the back surface of the substrate, and the diffusion of electrons in the negative electrode portion. Since it is set according to the constant, the hole collection ratio and the electron collection ratio are equal. As a result, in the present photovoltaic device, carriers can be collected most efficiently, so that power generation efficiency is improved.

キャリアが半導体基板中で拡散効果のみによって移動できる距離Ｌは、
Ｌ＝（Ｄ×τ）1/2
で示される。ここでＤはキャリアの拡散定数、τはキャリアのライフタイムである。この距離Ｌを半導体基板の厚さとすれば、最も効率的にキャリアを収集することができる。キャリアを正孔とした場合の距離Ｌａを受光面と正電極間の層厚ａとし、キャリアを電子とした場合の距離Ｌｂを受光面と負電極間の層厚ｂとすることによって、正および負のキャリアに対して最大の収集効率が得られる。半導体基板中における正孔と電子のライフタイムはほぼ同じであるため、距離Ｌａと距離Ｌｂの比は、Ｄhを正孔の拡散定数、Ｄeを電子の拡散定数とした場合、
Ｌａ：Ｌｂ＝（Ｄh）1/2：（Ｄe）1/2
となる。したがって、上記の層厚ａおよびｂを、
ａ：ｂ＝（Ｄh）1/2：（Ｄe）1/2
によって決定すれば、正負のキャリアに対して最大の収集効率が得られる。 The distance L that the carrier can move in the semiconductor substrate only by the diffusion effect is
L = (D × τ) 1/2
Indicated by Here, D is a carrier diffusion constant, and τ is a carrier lifetime. If this distance L is the thickness of the semiconductor substrate, carriers can be collected most efficiently. By setting the distance La when the carrier is a hole as the layer thickness a between the light receiving surface and the positive electrode and the distance Lb when the carrier is an electron as the layer thickness b between the light receiving surface and the negative electrode, Maximum collection efficiency is obtained for negative carriers. Since the lifetimes of holes and electrons in the semiconductor substrate are substantially the same, the ratio of distance La to distance Lb is such that D h is the hole diffusion constant and De is the electron diffusion constant.
La: Lb = (D h ) 1/2 : (D e ) 1/2
It becomes. Therefore, the above layer thicknesses a and b are
a: b = (D h ) 1/2 : (D e ) 1/2
The maximum collection efficiency can be obtained for positive and negative carriers.

なお、正孔の拡散定数Ｄh＝１２ｃｍ2／ｓ、電子の拡散定数Ｄe＝３６ｃｍ2／ｓであるシリコン半導体基板の場合、距離ａを８７μｍ、距離ｂを１５０μｍとした場合に効率よくキャリアを収集することができる。 In the case of a silicon semiconductor substrate having a hole diffusion constant D h = 12 cm 2 / s and an electron diffusion constant D e = 36 cm 2 / s, carriers are efficiently obtained when the distance a is 87 μm and the distance b is 150 μm. Can be collected.

また、正孔の拡散定数Ｄh＝６４ｃｍ2／ｓ、電子の拡散定数Ｄe＝１００ｃｍ2／ｓであるゲルマニウム半導体基板の場合、距離ａを１２０μｍ、距離ｂを１５０μｍとした場合に、効率よくキャリアを収集することができる。 Further, in the case of a germanium semiconductor substrate in which the hole diffusion constant D h = 64 cm 2 / s and the electron diffusion constant D e = 100 cm 2 / s, the distance a is 120 μm and the distance b is 150 μm. You can collect careers.

図２に本発明の一実施形態にかかる光起電力素子１０の断面構造を示す。図において、１１はｐ型またはｎ型の半導体基板、１２は電子収集層としてのｎ+層、１３は正孔収集層としてのｐ+層、１４は負電極、１５は正電極を示す。半導体基板１１の裏面側は、各電極とｎ+層またはｐ+層との接触部を残して表面保護膜（絶縁膜）１６ａによって被覆され、半導体基板１１の受光面側も表面保護膜１６ｂによって被覆されている。表面保護膜１６ｂ上には、反射防止膜１７が形成され、入射光が反射されず効率よく半導体基板に入射するようにされている。 FIG. 2 shows a cross-sectional structure of the photovoltaic device 10 according to one embodiment of the present invention. In the figure, 11 is a p-type or n-type semiconductor substrate, 12 is an n + layer as an electron collection layer, 13 is a p + layer as a hole collection layer, 14 is a negative electrode, and 15 is a positive electrode. The back surface side of the semiconductor substrate 11 is covered with a surface protective film (insulating film) 16a leaving a contact portion between each electrode and the n + layer or p + layer, and the light receiving surface side of the semiconductor substrate 11 is also covered with the surface protective film 16b. It is covered. An antireflection film 17 is formed on the surface protective film 16b so that incident light is efficiently reflected and incident on the semiconductor substrate.

半導体基板１１の正電極１５が形成されている部分の層厚ａと、負電極１４が形成されている部分の層厚ｂは、半導体基板１１における電子と正孔の拡散定数ＤeおよびＤhに基づいて決定され、したがって本光起電力素子１０では、基板の厚さが一様ではなく電極の極性毎に異なっている。具体的には、ａ：ｂ＝（Ｄh）1/2：（Ｄe）1/2となるように、層厚ａおよびｂを設定する。その結果、半導体基板の層厚ａおよびｂは、正孔および電子の拡散距離に対応した値をとるようになり、最も効率よくキャリアを収集することができる。 The layer thickness a of the portion of the semiconductor substrate 11 where the positive electrode 15 is formed and the layer thickness b of the portion where the negative electrode 14 is formed are the diffusion constants De and D h of electrons and holes in the semiconductor substrate 11. Therefore, in the present photovoltaic element 10, the thickness of the substrate is not uniform but varies depending on the polarity of the electrode. Specifically, the layer thicknesses a and b are set so that a: b = (D h ) 1/2 : (D e ) 1/2 . As a result, the layer thicknesses a and b of the semiconductor substrate have values corresponding to the diffusion distances of holes and electrons, and carriers can be collected most efficiently.

なお、例えば特許文献１乃至４に示した従来の光起電力素子では、半導体基板の厚さを一様としているため、その厚さを例えば電子の拡散距離に対応して設定すれば、正孔の収集割合が低下する。一方、半導体基板の厚さを正孔の拡散距離に対応して設定すれば、半導体基板の層厚が電子の拡散距離よりも小さくなり、受光層としての充分な厚さを確保することができない。これに対して、本発明の光起電力素子１０では、半導体基板の層厚が正電極部分と負電極部分でそれぞれ最適化されているので、最大のキャリア収集効率を得ることができ、その結果、発電効率も向上する。   For example, in the conventional photovoltaic elements shown in Patent Documents 1 to 4, since the thickness of the semiconductor substrate is uniform, if the thickness is set corresponding to the diffusion distance of electrons, for example, holes The collection rate of will decrease. On the other hand, if the thickness of the semiconductor substrate is set corresponding to the hole diffusion distance, the layer thickness of the semiconductor substrate becomes smaller than the electron diffusion distance, and a sufficient thickness as the light receiving layer cannot be secured. . On the other hand, in the photovoltaic device 10 of the present invention, since the layer thickness of the semiconductor substrate is optimized in each of the positive electrode portion and the negative electrode portion, the maximum carrier collection efficiency can be obtained. The power generation efficiency is also improved.

本実施形態による光起電力素子１０の具体例を下記に示す。なお、光起電力素子１０を構成するバルクは、単結晶Ｓｉによって形成されているものとする。また、Ｃはキャリア濃度を示す。   A specific example of the photovoltaic element 10 according to the present embodiment is shown below. In addition, the bulk which comprises the photovoltaic element 10 shall be formed with single crystal Si. C represents the carrier concentration.

（実施例１）
半導体基板（光吸収部）１１：ｐ型Ｓｉ基板、Ｃ＝１×１０14ｃｍ-3
ａ＝８７μｍ、ｂ＝１５０μｍ（ＳｉのＤe＝３６ｃｍ2／ｓ、Ｄh＝１２ｃｍ2／ｓ）
電子収集部１２：ｎ+型Ｓｉ層、Ｃ＝１×１０19ｃｍ-3、拡散深さ１μｍ
正孔収集部１３：ｐ+型Ｓｉ層、Ｃ＝１×１０19ｃｍ-3、拡散深さ１μｍ
負電極１４：Ａｌ、膜厚２μｍ
正電極１５：Ａｌ、膜厚２μｍ
表面保護膜１６ａ：ＳｉＯ2、膜厚０．１μｍ
表面保護膜１６ｂ：ＳｉＯ2、膜厚１０ｎｍ
反射防止膜１７：ＭｇＦ2／ＺｎＳの２層膜、膜厚１１０ｎｍ／５０ｎｍ Example 1
Semiconductor substrate (light absorption part) 11: p-type Si substrate, C = 1 × 10 14 cm −3
a = 87μm, b = 150μm ( Si of D e = 36cm 2 / s, D h = 12cm 2 / s)
Electron collector 12: n + type Si layer, C = 1 × 10 19 cm −3 , diffusion depth 1 μm
Hole collector 13: p + type Si layer, C = 1 × 10 19 cm −3 , diffusion depth 1 μm
Negative electrode 14: Al, film thickness 2 μm
Positive electrode 15: Al, film thickness 2 μm
Surface protective film 16a: SiO 2 , film thickness 0.1 μm
Surface protective film 16b: SiO 2 , film thickness 10 nm
Antireflection film 17: MgF 2 / ZnS two-layer film, film thickness 110 nm / 50 nm

（実施例２）
半導体基板（光吸収部）１１：ｐ型Ｇｅ基板、Ｃ＝１×１０15ｃｍ-3
ａ＝１２０μｍ、ｂ＝１５０μｍ（ＧｅのＤe＝１００ｃｍ2／ｓ、Ｄh＝６４ｃｍ2／ｓ）
電子収集部１２：ｎ+型Ｇｅ層、Ｃ＝１×１０19ｃｍ-3、拡散深さ１μｍ
正孔収集部１３：ｐ+型Ｇｅ層、Ｃ＝１×１０19ｃｍ-3、拡散深さ１μｍ
負電極１４：Ａｌ、膜厚２μｍ
正電極１５：Ａｌ、膜厚２μｍ
表面保護膜１６ａ：ＳｉＮx、膜厚０．１μｍ
表面保護膜１６ｂ：ＳｉＮx、膜厚１０ｎｍ
反射防止膜１７：ＳｉＯ2／ＴｉＯ2の２層膜、膜厚１００ｎｍ／６０ｎｍ (Example 2)
Semiconductor substrate (light absorption part) 11: p-type Ge substrate, C = 1 × 10 15 cm −3
a = 120μm, b = 150μm ( Ge of D e = 100cm 2 / s, D h = 64cm 2 / s)
Electron collector 12: n + -type Ge layer, C = 1 × 10 19 cm −3 , diffusion depth 1 μm
Hole collector 13: p + type Ge layer, C = 1 × 10 19 cm −3 , diffusion depth 1 μm
Negative electrode 14: Al, film thickness 2 μm
Positive electrode 15: Al, film thickness 2 μm
Surface protective film 16a: SiN x , film thickness 0.1 μm
Surface protective film 16b: SiN x , film thickness 10 nm
Antireflection film 17: SiO 2 / TiO 2 bilayer film, film thickness 100 nm / 60 nm

上記実施例１および２では、半導体基板材料としてＳｉおよびＧｅを挙げているが、ＳｉＧｅ、ＳｉＣ、Ｃ等のＩＶ族半導体材料を用いても同様な効果が得られることは勿論である。また、半導体基板をｐ型半導体によって構成しているが、ｎ型半導体であっても良い。さらにまた、本発明の特徴を、背景技術の項で説明した従来例としての光起電力素子の構成に組み込むことにより、さらに光電変換効率を改善して発電効率の高い光起電力素子を得ることができる。   In Examples 1 and 2 above, Si and Ge are cited as semiconductor substrate materials, but it is needless to say that similar effects can be obtained even when IV group semiconductor materials such as SiGe, SiC, and C are used. Moreover, although the semiconductor substrate is composed of a p-type semiconductor, it may be an n-type semiconductor. Furthermore, by incorporating the features of the present invention into the configuration of the conventional photovoltaic device described in the background section, a photovoltaic device with higher power generation efficiency can be obtained by further improving the photoelectric conversion efficiency. Can do.

従来の光起電力素子の断面構造を示す図。The figure which shows the cross-section of the conventional photovoltaic device. 本発明の一実施形態にかかる光起電力素子の断面構造を示す図。The figure which shows the cross-section of the photovoltaic device concerning one Embodiment of this invention.

符号の説明Explanation of symbols

１１ 半導体基板
１２ 電子収集部
１３ 正孔収集部
１４ 負電極
１５ 正電極
１６ａ、１６ｂ 表面保護膜
１７ 反射防止膜 DESCRIPTION OF SYMBOLS 11 Semiconductor substrate 12 Electron collecting part 13 Hole collecting part 14 Negative electrode 15 Positive electrode 16a, 16b Surface protective film 17 Antireflection film

Claims (4)

半導体基板の受光面とは反対側の裏面に正および負の電極を配置した裏面電極型の光起電力素子において、前記半導体基板の前記受光面と前記正電極間の層厚ａを正孔の拡散定数に基づいて決定し、前記受光面と前記負電極間の層厚ｂを電子の拡散定数に基づいて決定したことを特徴とする、光起電力素子。   In a back electrode type photovoltaic device in which positive and negative electrodes are arranged on the back surface opposite to the light receiving surface of the semiconductor substrate, the layer thickness a between the light receiving surface and the positive electrode of the semiconductor substrate is set to the hole thickness. A photovoltaic element, wherein the photovoltaic element is determined based on a diffusion constant, and a layer thickness b between the light receiving surface and the negative electrode is determined based on an electron diffusion constant. 請求項１に記載の光起電力素子において、Ｄｈを前記半導体基板中の正孔の拡散定数、Ｄｅを同じく電子の拡散定数とした場合、前記層厚ａおよびｂは、以下の式、
ａ：ｂ＝（Ｄｈ）１／２：（Ｄｅ）１／２
に従って決定されることを特徴とする、光起電力素子。 In the photovoltaic device according to claim 1, the diffusion constant of holes in the semiconductor substrate to D h, when the diffusion constant of the same electrons D e, the layer thickness a and b, the following equation,
a: b = (D h ) 1/2 : (D e ) 1/2
A photovoltaic device, characterized in that it is determined according to: 請求項２に記載の光起電力素子において、前記半導体基板をｐ型シリコン基板で構成し、前記層厚ａを８７μｍ、前記層厚ｂを１５０μｍとしたことを特徴とする、光起電力素子。   3. The photovoltaic device according to claim 2, wherein the semiconductor substrate is a p-type silicon substrate, the layer thickness a is 87 [mu] m, and the layer thickness b is 150 [mu] m. 請求項２に記載の光起電力素子において、前記半導体基板をｐ型ゲルマニウムで構成し、前記層厚ａを１２０μｍ、前記層厚ｂを１５０μｍとしたことを特徴とする、光起電力素子。   3. The photovoltaic element according to claim 2, wherein the semiconductor substrate is made of p-type germanium, the layer thickness a is 120 [mu] m, and the layer thickness b is 150 [mu] m.
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