JP5784358B2 - Photoelectric conversion element and solar cell - Google Patents
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Description
本発明の実施形態は、光電変換素子および太陽電池に関する。 Embodiments described herein relate generally to a photoelectric conversion element and a solar cell.
例えば、太陽電池において、半導体薄膜を光吸収層として用いる化合物薄膜光電変換素子の開発が進んできており、Iｂ族、ＩＩＩｂ族とＶＩｂ族から構成されカルコパイライト構造をもつ化合物半導体の中で、Ｃｕ、Ｉｎ、Ｇａ及びＳｅから成るＣｕ（Ｉｎ，Ｇａ）Ｓｅ２、いわゆるＣＩＧＳを光吸収層とした薄膜太陽電池等の光電変換素子が注目されている。その変換効率を向上させるために、結晶成長の促進や欠陥低減による膜質向上など様々な試みがなされており、その一つにバンドギャップ分布形成技術がある。バンドギャップ分布は、ＣＩＧＳ光吸収層の膜厚方向でＧａとＩｎの組成比を変化させることで形成される。ＣＩＧＳでＧａとＩｎの組成比を変化させると、Ｇａ組成比が多い組成でバンドギャップが広くなり、Ｉｎ組成比が多い組成でバンドギャップが狭くなる。ＧａとＩｎの組成比の変調によるバンドギャップの調整では、主に伝導体レベルが変化するため、ＣＩＧＳ光吸収層の裏面電極側のＧａ組成比を高く、ＣＩＧＳ光吸収層表面のＧａ組成比を低くすることで、内部電界が生じ、光励起されたキャリアは裏面電極側からｐｎ接合界面方向へと移動し、キャリア吸収効率が向上する。光電変換素子の光吸収層では、ｐｎ接合界面側で短波長の光を吸収し、裏面電極側で長波長の光を吸収する。しかしながら、ＧａとＩｎの組成比の変化によるバンドギャップ分布の形成では、主に伝導体レベルが変化し、価電子帯レベルはほとんど変化しないため、ｐｎ接合界面側でバンドギャップが狭く、裏面電極側でバンドギャップが広くなるなり、取り込める光の波長がｐｎ接合界面側のバンドギャップで制限され、効率的に光吸収できない。 For example, in a solar cell, a compound thin film photoelectric conversion element using a semiconductor thin film as a light absorption layer has been developed. Among compound semiconductors having a chalcopyrite structure composed of Ib group, IIIb group and VIb group, Cu Attention has been focused on photoelectric conversion elements such as thin-film solar cells using Cu (In, Ga) Se 2 , which is made of In, Ga and Se, so-called CIGS as a light absorption layer. In order to improve the conversion efficiency, various attempts have been made such as promoting crystal growth and improving film quality by reducing defects, one of which is a band gap distribution forming technique. The band gap distribution is formed by changing the composition ratio of Ga and In in the film thickness direction of the CIGS light absorption layer. When the composition ratio of Ga and In is changed by CIGS, the band gap is widened with a composition having a large Ga composition ratio, and the band gap is narrowed with a composition having a large In composition ratio. In adjustment of the band gap by modulation of the composition ratio of Ga and In, since the conductor level mainly changes, the Ga composition ratio on the back electrode side of the CIGS light absorption layer is high, and the Ga composition ratio on the CIGS light absorption layer surface is set to be high. By making it low, an internal electric field is generated, and the photoexcited carriers move from the back electrode side toward the pn junction interface, improving the carrier absorption efficiency. The light absorption layer of the photoelectric conversion element absorbs short wavelength light on the pn junction interface side and absorbs long wavelength light on the back electrode side. However, in forming a band gap distribution by changing the composition ratio of Ga and In, the conductor level mainly changes and the valence band level hardly changes. Therefore, the band gap is narrow on the pn junction interface side, and the back electrode side As a result, the band gap becomes wider, and the wavelength of light that can be taken in is limited by the band gap on the pn junction interface side, so that light cannot be absorbed efficiently.
また、バンドギャップは同じ構成元素で、Iｂ族、ＩＩＩｂ族とＶＩｂ族の構成比を変えることでも変化させることができる。カルコパイライト構造中のIｂ族元素をＩＩＩｂ族元素に置き換え、さらにI族元素を取り除いた空孔配列型カルコパイライト（ＯＶＣ）構造とすることで、カルコパイライト構造をもつ化合物半導体に比べて、ＩＩＩｂ族／Iｂ族モル比及びバンドギャップは共に大きくなる。さらに、ＯＶＣ構造とすることで、伝導体レベル及び価電子帯レベルが共に真空準位から深くなる。ＶＩｂ族元素がＳから成るカルコパイライト薄膜光電変換素子で、ｐ型光吸収層とｎ層間にＩＩＩｂ族／Ｃｕモル比が、ｐ型光吸収層よりも大きな中間層を形成し、光吸収層と中間層界面で生ずる電界によるドリフトで光照射により生成した少数キャリアを高速に移動させ、キャリアの再結合を抑制している。しかしながら、中間層内での伝導体レベル及び価電子帯レベルが平坦であり、生成したキャリアが再結合しやすく、さらに、ｐ型光吸収層内部で長波長の光により生成したキャリアを効果的に移動させることが困難である。 The band gap is the same constituent element, and can be changed by changing the constituent ratio of the Ib group, IIIb group and VIb group. By replacing the group Ib element in the chalcopyrite structure with a group IIIb element and removing the group I element to form a hole-arranged chalcopyrite (OVC) structure, the group IIIb group compared to a compound semiconductor having a chalcopyrite structure The / Ib group molar ratio and the band gap both increase. Furthermore, with the OVC structure, both the conductor level and the valence band level become deeper from the vacuum level. In the chalcopyrite thin film photoelectric conversion element in which the VIb group element is S, an intermediate layer having a IIIb group / Cu molar ratio larger than that of the p-type light absorption layer is formed between the p-type light absorption layer and the n layer, Minority carriers generated by light irradiation are moved at high speed by drift due to an electric field generated at the interface of the intermediate layer, thereby suppressing carrier recombination. However, the conductor level and valence band level in the intermediate layer are flat, the generated carriers are likely to recombine, and the carriers generated by the long wavelength light inside the p-type light absorption layer are effectively It is difficult to move.
実施形態は、高い変換効率の光電変換素子および太陽電池を提供することを目的とする。 An object of the embodiment is to provide a photoelectric conversion element and a solar cell with high conversion efficiency.
実施形態の光電変換素子は、Ｃｕと、Ａｌ、Ｉｎ及びＧａからなる群より選ばれる少なくとも一つのＩＩＩｂ族元素と、Ｏ、Ｓ、Ｓｅ及びＴｅからなる群より選ばれる少なくとも一つのＩＶｂ族元素を含みカルコパイライト型構造を有するｐ型光吸収層を、ｎ型化合物半導体層と裏面電極との間に具備し、前記ＩＩＩｂ族元素と前記Ｃｕとのモル比であるＩＩＩｂ族/Ｃｕモル比が、前記ｎ型化合物半導体層との界面側から前記裏面電極側の界面に向かって減少する傾斜組成部を前記ｐ型光吸収層の少なくとも前記ｎ型化合物半導体層との界面から有することを特徴とする。
また、他の実施形態の太陽電池は、前記実施形態の光電変換素子を用いてなることを特徴とする。
The photoelectric conversion element of the embodiment includes at least one group IIIb element selected from the group consisting of Cu, Al, In, and Ga, and at least one group IVb element selected from the group consisting of O, S, Se, and Te. A p-type absorber layer having a chalcopyrite structure is provided between the n-type compound semiconductor layer and the back electrode, and the IIIb group / Cu molar ratio, which is the molar ratio of the group IIIb element to the Cu, and having a gradient composition portion which decreases from the interface side between the n-type compound semiconductor layer at the interface of the back surface electrode side from the interface between at least the n-type compound semiconductor layer of the p-type light absorbing layer .
Moreover, the solar cell of other embodiment uses the photoelectric conversion element of the said embodiment, It is characterized by the above-mentioned.
以下、本発明を実施するための形態について図面を参照して詳細に説明する。
図１の概念図に示す光電変換素子１０は、基板１１と、前記基板上に設けられた裏面電極１２と、前記裏面電極１２上に設けられた第１の取り出し電極１３と、前記裏面電極１２上に設けられた光吸収層１４と、前記光吸収層１４上に設けられたバッファー層１５（１５ａ、１５ｂ）と、前記バッファー層１５上に設けられた透明電極層１６と、前記透明電極層１６上に設けられた第２の取り出し電極１７と、前記透明電極層１６上に設けられた反射防止膜１８とを少なくとも備えている。
Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
The photoelectric conversion element 10 shown in the conceptual diagram of FIG. 1 includes a substrate 11, a back electrode 12 provided on the substrate, a first extraction electrode 13 provided on the back electrode 12, and the back electrode 12. A light absorption layer 14 provided thereon, a buffer layer 15 (15a, 15b) provided on the light absorption layer 14, a transparent electrode layer 16 provided on the buffer layer 15, and the transparent electrode layer 16 is provided with at least a second extraction electrode 17 provided on 16 and an antireflection film 18 provided on the transparent electrode layer 16.
実施形態の光吸収層（ｐ型）１４は、Ｃｕと、Ａｌ、Ｉｎ及びＧａからなる群より選ばれる少なくとも一つのＩＩＩｂ族元素と、Ｏ、Ｓ、Ｓｅ及びＴｅからなる群より選ばれる少なくとも一つのＶＩｂ族元素からなり、その構成元素の種類は光吸収層１４全領域で同じであることが好ましく、結晶構造はカルコパイライト構造若しくは空孔配列型カルコパイライト構造を有することが望まれる。光吸収層１４の少なくとも一部に傾斜組成部が含まれることが好ましい。
なお、実施形態において、カルコパイライト構造と空孔配列型カルコパイライト構造は、それぞれを別に説明している場合を除き、両者をカルコパイライト構造として記載する。
The light absorption layer (p-type) 14 of the embodiment is at least one selected from the group consisting of Cu, at least one group IIIb element selected from the group consisting of Al, In and Ga, and O, S, Se and Te. It consists of two VIb group elements, and the kind of the constituent elements is preferably the same in the entire region of the light absorption layer 14, and the crystal structure is desired to have a chalcopyrite structure or a pore arrangement type chalcopyrite structure. It is preferable that a gradient composition part is included in at least a part of the light absorption layer 14.
In the embodiment, the chalcopyrite structure and the hole-arranged chalcopyrite structure are both described as a chalcopyrite structure unless otherwise described.
ここで、傾斜組成部とは、断面膜厚方向の直線上で、ｎ型化合物半導体層との界面と裏面電極との界面を１０等配分した１１点で測定したＩＩＩｂ族／Ｃｕモル比が変化する領域である。実施形態において、１１点のＩＩＩｂ族／Ｃｕモル比変化によって、傾斜の形態を判断する。ｎ型化合物半導体層とのｐｎ界面側から裏面電極との界面に向かって、ＩＩＩｂ族／Ｃｕモル比が減少すると価電子帯上端（ＶＢＭ）に傾斜ができ、キャリアが移動しやすくなり、キャリアの再結合を抑制しやすくなることが好ましい。傾斜が逆方向であると、ｐｎ界面でのキャリアの移動度は上がらないため、好ましくない。ＩＩＩｂ族／Ｃｕモル比が常に減少（連続的変化）する形態であると、キャリアが停滞することなく移動できるという理由により望ましく、一部変化しない（断続的変化）平坦領域があることは許容される。なお、逆にｐｎ界面から裏面電極に向かってＩＩＩｂ族／Ｃｕモル比が増える領域が含まれると、その領域内でキャリアの移動が阻害されてしまうため好ましくない。この逆の領域は、不可避的な場合を除いて含まれないことが好ましい。 Here, the graded composition part is a change in the IIIb group / Cu molar ratio measured at 11 points on the straight line in the cross-sectional film thickness direction, with 10 equal distributions of the interface between the n-type compound semiconductor layer and the back electrode. It is an area to do. In the embodiment, the shape of the slope is determined by the 11 point group IIIb / Cu molar ratio change. When the IIIb group / Cu molar ratio decreases from the pn interface side with the n-type compound semiconductor layer toward the interface with the back electrode, the valence band top (VBM) can be inclined, and carriers can move easily. It is preferable that recombination is easily suppressed. If the inclination is in the reverse direction, the carrier mobility at the pn interface does not increase, which is not preferable. It is desirable that the group IIIb / Cu molar ratio is constantly decreasing (continuous change) because carriers can move without stagnation, and it is allowed to have a flat region that does not change partially (intermittent change). The On the contrary, if a region where the IIIb group / Cu molar ratio increases from the pn interface toward the back electrode is included, it is not preferable because the movement of carriers is inhibited in the region. It is preferable that the opposite area is not included unless it is inevitable.
キャリアの再結合を抑制する観点から、傾斜組成部が断面膜厚方向の直線上に、２部以上少なくともあることが好ましい。また、同じ観点から、対数関数又は反比例関数型又はその類似型の曲線又は略曲線を描くように、光吸収層１４のｐｎ界面側から、裏面電極１２側に向かって減少する傾斜組成部が１部以上含まれることが好ましい。 From the viewpoint of suppressing carrier recombination, it is preferable that the gradient composition part is at least 2 parts on a straight line in the cross-sectional film thickness direction. Further, from the same point of view, the gradient composition portion that decreases from the pn interface side of the light absorption layer 14 toward the back electrode 12 side so as to draw a logarithmic function, an inverse proportional function type curve, or a similar type curve or a substantially curved line, is 1 It is preferable that more than part is contained.
ＩＩＩｂ族／Ｃｕモル比の組成分析は断面ＳＥＭ／ＥＤＸ測定測定の点分析（ＳＥＭ：走査型電子顕微鏡（ｓｃａｎｎｉｎｇ ｅｌｅｃｔｒｏｎ ｍｉｃｒｏｓｃｏｐｅ）、ＥＤＸ：エネルギー分散型Ｘ線分光法（Ｅｎｅｒｇｙ Ｄｉｓｐｅｒｓｉｖｅ Ｘ−ｒａｙ Ｓｐｅｃｔｒｏｓｃｏｐｙ））で行う。測定は、光電変換素子１０の中心で行う。ＩＩＩｂ族／Ｃｕモル比は、光電変換素子１０の中心部分をへき開し、断面膜厚方向の同一深度の５点平均値である。５点の定め方は、２万倍の断面ＳＥＭ像を観察し、その断面ＳＥＭ像を膜厚方向と直交する方向に５等分割し、分割された領域の中心点とする。この中心点を膜厚方向に上記の１１点測定をし、ＩＩＩ族ｂ／Ｃｕモル比の変化量を測定する。ｎ型化合物半導体層との界面及び裏面電極との界面は、断面ＳＥＭ／ＥＤＸ測定でｎ型化合物半導体層及び裏面電極の構成成分が含まれないｐ型化合物半導体の測定位置として定義する。 Composition analysis of IIIb group / Cu molar ratio is cross-sectional SEM / EDX measurement measurement point analysis (SEM: scanning electron microscope, EDX: energy dispersive X-ray spectroscopy) To do. The measurement is performed at the center of the photoelectric conversion element 10. The IIIb group / Cu molar ratio is a five-point average value at the same depth in the cross-sectional film thickness direction by cleaving the central portion of the photoelectric conversion element 10. The method of determining the five points is to observe a cross-sectional SEM image of 20,000 times, divide the cross-sectional SEM image into five equal parts in a direction orthogonal to the film thickness direction, and use it as the center point of the divided region. The eleven points are measured at the center point in the film thickness direction, and the amount of change in the group III b / Cu molar ratio is measured. The interface with the n-type compound semiconductor layer and the interface with the back electrode are defined as measurement positions of the p-type compound semiconductor that do not include the components of the n-type compound semiconductor layer and the back electrode in the cross-sectional SEM / EDX measurement.
さらに、図２のグラフに示すように、ｎ型化合物半導体層との界面でのＩＩＩｂ族/Ｃｕモル比をｘ１、ｐ型光吸収層の層厚方向の中心点でのＩＩＩｂ族/Ｃｕモル比をｘ２（ｔ／２）、裏面電極との界面でのＩＩＩｂ族/Ｃｕモル比をｘ３（ｔ）とすると、キャリア再結合抑制の観点から、少なくともｘ１≧ｘ２≧ｘ３を満たすことが好ましく、ｘ１＞ｘ２＞ｘ３を満たすことがより好ましい。ＩＩＩｂ族/Ｃｕモル比が大きい（例えば１より大きい）と、フェルミ準位がＶＢＭから離れる。また、ＩＩＩｂ族/Ｃｕモル比が比較的小さい（例えば１）と、前者よりもフェルミ準位がＶＢＭに近づく。従って、Ｃｕに対してＩＩＩｂ族過剰領域では、キャリアの再結合の確率が高いため、このｐｎ界面近傍の領域においてキャリアの移動度を上げることが好ましい。そこで、ｘ１，ｘ２とｘ３は、（ｘ１−ｘ２）＞（ｘ２−ｘ３）であることがより好ましい。 Furthermore, as shown in the graph of FIG. 2, the group IIIb / Cu molar ratio at the interface with the n-type compound semiconductor layer is x1, and the group IIIb / Cu molar ratio at the center point in the layer thickness direction of the p-type light absorption layer. X2 (t / 2) and the group IIIb / Cu molar ratio at the interface with the back electrode is x3 (t), it is preferable to satisfy at least x1 ≧ x2 ≧ x3 from the viewpoint of suppressing carrier recombination, It is more preferable to satisfy> x2> x3. When the group IIIb / Cu molar ratio is large (for example, larger than 1), the Fermi level is separated from the VBM. Further, when the group IIIb / Cu molar ratio is relatively small (for example, 1), the Fermi level is closer to VBM than the former. Therefore, since the probability of carrier recombination is high in the group IIIb excess region with respect to Cu, it is preferable to increase the carrier mobility in the region near the pn interface. Therefore, x1, x2, and x3 are more preferably (x1-x2)> (x2-x3).
また、図３に示すようにＩＩＩｂ族/Ｃｕモル比が大きいと、ＶＢＭが小さくなりバンドギャップが大きく、ＩＩＩｂ族/Ｃｕモル比が小さいと、ＶＢＭが大きくバンドギャップが小さくなる。ｎ型化合物半導体層との界面での光吸収層のバンドギャップをＥｇ１、ｐ型光吸収層の層厚の中心点でのバンドギャップをＥｇ２、裏面電極との界面での光吸収層のバンドギャップをＥｇ３とした時、（Ｅｇ１−Ｅｇ２）＞（Ｅｇ２−Ｅｇ３）であることがより好ましい。これにより、短波長の光はｐｎ接合界面側で吸収し、長波長の光は裏面電極側で吸収することになり、効率的なバンドギャップ分布を形成していると言える。 Further, as shown in FIG. 3, when the IIIb group / Cu molar ratio is large, the VBM is small and the band gap is large, and when the IIIb group / Cu molar ratio is small, the VBM is large and the band gap is small. The band gap of the light absorption layer at the interface with the n-type compound semiconductor layer is Eg1, the band gap at the center point of the layer thickness of the p-type light absorption layer is Eg2, and the band gap of the light absorption layer at the interface with the back electrode Is more preferably (Eg1-Eg2)> (Eg2-Eg3). Accordingly, short wavelength light is absorbed on the pn junction interface side, and long wavelength light is absorbed on the back electrode side, and it can be said that an efficient band gap distribution is formed.
以下、ＣｕとＩｎとＴｅから成る光吸収層を例に特徴を述べる。
図４にＣｕとＩｎとＴｅを構成元素とする半導体薄膜のフェルミ準位ＥＦと伝導体下端（ＣＢＭ）と価電子帯上端（ＶＢＭ）を示す。Ｉｎ／Ｃｕモル比を大きくすると、ＣＢＭ及びＶＢＭ共に真空準位から離れる方向に変化するため、Ｉｎ／Ｃｕモル比をｎ型化合物半導体層との界面側から裏面電極側の界面に向かって減少する傾斜組成部を少なくともその一部に形成する。それにより、光励起により生成した電子はｐｎ接合界面方向へ移動し、ホールは裏面電極方向へ移動することになる。一方で、Ｉｎ／Ｃｕモル比が大きい薄膜では、フェルミ準位が、ＶＢＭから離れるため、ｐｎ接合界面を形成すると、Ｉｎ／Ｃｕモル比が小さい薄膜に比べて、界面でのキャリアの再結合が起こりやすくなる。また、図５と図６の表面ＳＥＭ像を比較すると、Ｉｎ／Ｃｕモル比が小さい薄膜では、結晶粒径が小さくなっており、それに伴って、結晶粒界が増え、キャリア再結合中心になりやすくなる。このｐｎ接合界面近傍でのキャリア再結合は、Ｉｎ／Ｃｕモル比の変化により、光励起で生成したホールをｐｎ接合界面から早く移動させることにより低減できる。
Hereinafter, the characteristics will be described by taking a light absorption layer made of Cu, In and Te as an example.
Figure 4 shows the Fermi level E F and conductor lower end of the semiconductor thin film as constituent elements Cu and In and Te (CBM) and valence band maximum (VBM). When the In / Cu molar ratio is increased, both the CBM and VBM change in a direction away from the vacuum level, so the In / Cu molar ratio decreases from the interface side with the n-type compound semiconductor layer toward the interface on the back electrode side. The gradient composition part is formed on at least a part thereof. Thereby, electrons generated by photoexcitation move toward the pn junction interface, and holes move toward the back electrode. On the other hand, in a thin film having a large In / Cu molar ratio, the Fermi level is separated from the VBM. Therefore, when a pn junction interface is formed, carrier recombination at the interface is reduced compared to a thin film having a small In / Cu molar ratio. It tends to happen. Further, comparing the surface SEM images of FIG. 5 and FIG. 6, in the thin film having a small In / Cu molar ratio, the crystal grain size becomes small, and accordingly, the crystal grain boundary increases and becomes a carrier recombination center. It becomes easy. This carrier recombination in the vicinity of the pn junction interface can be reduced by moving holes generated by photoexcitation early from the pn junction interface due to a change in the In / Cu molar ratio.
また、図４からわかるように、ｐｎ界面から裏面電極方向に光吸収層のＩｎ／Ｃｕ比を大きくすることで、（Ｅｇ１−Ｅｇ２）＞（Ｅｇ２−Ｅｇ３）を満たすことも上述の理由により好ましい。 Further, as can be seen from FIG. 4, it is also preferable for the above reason to satisfy (Eg1-Eg2)> (Eg2-Eg3) by increasing the In / Cu ratio of the light absorption layer from the pn interface toward the back electrode. .
以下、光電変換素子に用いる光吸収層１４以外の構成について説明する。
基板１１としては、青板ガラスを用いることが望ましく、ステンレス、Ｔｉ又はＣｒ等の金属板あるいはポリイミド等の樹脂を用いることもできる。
Hereinafter, configurations other than the light absorption layer 14 used in the photoelectric conversion element will be described.
As the substrate 11, it is desirable to use blue plate glass, and it is also possible to use a metal plate such as stainless steel, Ti or Cr, or a resin such as polyimide.
裏面電極１２としては、ＭｏやＷ等の導電性の金属膜を用いることができる。その中でも、Ｍｏ膜を用いることが望ましい。 As the back electrode 12, a conductive metal film such as Mo or W can be used. Among these, it is desirable to use a Mo film.
取り出し電極１３，１７としては、例えば、Ａｌ、Ａｇ或いはＡｕ等の導電性の金属膜を用いることができる。さらに、透明電極１５との密着性を向上させるために、Ｎｉ或いはＣｒを堆積させた後、Ａｌ、Ａｇ或いはＡｕを堆積させてもよい。 As the extraction electrodes 13 and 17, for example, a conductive metal film such as Al, Ag, or Au can be used. Furthermore, in order to improve the adhesion with the transparent electrode 15, after depositing Ni or Cr, Al, Ag or Au may be deposited.
バッファー層１５としては、ＣｄＳ、Ｚｎ（Ｏ，Ｓ，ＯＨ）或いはＭｇを添加したＺｎＯを用いることができる。光吸収層１４であるカルコパイライト型化合物半導体はｐ型半導体として、ＣｄＳあるいはＺｎＯ：Ｍｇに代表されるバッファー層１５ａはｎ型半導体として、ＺｎＯに代表されるバッファー層１５ｂはｎ＋型層として機能すると考えられる。ｐｎ接合界面で伝導帯不連続量（ＣＢＯ）ΔＥｃを誘起するようにバッファー層１５ａの材料を選定することによりキャリアの再結合を低減できる。 As the buffer layer 15, CdS, Zn (O, S, OH), or ZnO added with Mg can be used. The chalcopyrite compound semiconductor that is the light absorption layer 14 functions as a p-type semiconductor, the buffer layer 15a typified by CdS or ZnO: Mg functions as an n-type semiconductor, and the buffer layer 15b typified by ZnO functions as an n + -type layer. I think that. By selecting the material of the buffer layer 15a so as to induce a conduction band discontinuity (CBO) ΔEc at the pn junction interface, carrier recombination can be reduced.
透明電極層１６は太陽光などの光を透過し、尚且つ導電性を有することが必要であり、例えば、アルミナ（Ａｌ２Ｏ３）を２ｗｔ％含有したＺｎＯ：Ａｌ或いはジボランからのＢをドーパントとしたＺｎＯ：Ｂを用いることができる。
反射防止膜１８としては、例えば、ＭｇＦ２を用いることが望ましい。
The transparent electrode layer 16 is required to transmit light such as sunlight and to have conductivity, for example, ZnO: Al containing 2 wt% of alumina (Al 2 O 3 ) or B from diborane as a dopant. ZnO: B can be used.
For example, MgF 2 is desirably used as the antireflection film 18.
図１の光電変換素子１０の製造方法としては、以下の方法を例として挙げる。
なお、下記の製造方法の一例であり、適宜変更しても構わない。従って、工程の順序を変更してもよいし、複数の工程を併合してもよい。
As a manufacturing method of the photoelectric conversion element 10 of FIG.
In addition, it is an example of the following manufacturing method, You may change suitably. Therefore, the order of the steps may be changed, or a plurality of steps may be combined.
［基板に裏面電極を成膜する工程］
基板１１上に、裏面電極１２を成膜する。成膜方法としては、例えば、導電性金属よりなるスパッタターゲットを用いたスパッタ法等の薄膜形成方法が挙げられる。
[Step of depositing back electrode on substrate]
A back electrode 12 is formed on the substrate 11. Examples of the film forming method include a thin film forming method such as a sputtering method using a sputtering target made of a conductive metal.
[裏面電極上に光吸収層を成膜する工程］
裏面電極１２を堆積後、光吸収層１４となる化合物半導体薄膜を堆積する。なお、裏面電極１２には光吸収層１４と第１の取り出し電極１３を堆積するため、第１の取り出し電極１３を堆積する部位を少なくとも除く裏面電極１２上の一部に光吸収層１４を堆積する。成膜方法として、Ｃｕと、ＩＩＩｂ族元素及びＶＩｂ族元素をスパッタ法で、独立に原料供給する。ＩＩＩｂ族／Ｃｕモル比が裏面電極側から大きくなるように出力を調整することで、傾斜組成を形成することができる。ＩＩＩｂ族／Ｃｕモル比が調整可能であれば、３元ではなく、２元同時スパッタでもよい。キャリアの移動度を早くし、キャリアの再結合を抑制するためには、出力の調整回数が少なくとも２回以上であることが好ましく、その回数が多いことは好ましい。出力変化を連続的に行い、ＩＩＩｂ族／Ｃｕモル比が直線的又は曲線的に変化するように出力調整することも好ましい。その際、ＶＩｂ族元素は欠損と成らないように供給過多にしてもよい。スパッタするためのエネルギー出力を大きく変化させて、組成変調範囲を広げるため、Ｃｕ及びＩＩＩｂ族元素は、高エネルギーでスパッタすることができるＤＣスパッタが好ましい。ＶＩｂ族元素の供給方法はスパッタ法に限らず、蒸着法により供給することもできる。
[Step of depositing light absorption layer on back electrode]
After the back electrode 12 is deposited, a compound semiconductor thin film that becomes the light absorption layer 14 is deposited. Since the light absorption layer 14 and the first extraction electrode 13 are deposited on the back electrode 12, the light absorption layer 14 is deposited on a part of the back electrode 12 excluding at least the portion where the first extraction electrode 13 is deposited. To do. As a film forming method, Cu, a group IIIb element and a group VIb element are independently supplied by sputtering. A gradient composition can be formed by adjusting the output so that the IIIb group / Cu molar ratio increases from the back electrode side. If the IIIb group / Cu molar ratio can be adjusted, two-way simultaneous sputtering may be used instead of three-way. In order to increase carrier mobility and suppress carrier recombination, the number of output adjustments is preferably at least two, and it is preferable that the number of adjustments is large. It is also preferable to continuously adjust the output and adjust the output so that the IIIb group / Cu molar ratio changes linearly or curvedly. At that time, the VIb group element may be excessively supplied so as not to be deficient. In order to greatly change the energy output for sputtering and widen the composition modulation range, the Cu and IIIb group elements are preferably DC sputtering that can be sputtered with high energy. The supply method of the VIb group element is not limited to the sputtering method, and can be supplied by a vapor deposition method.
［光吸収層上にバッファー層を成膜する工程］
得られた光吸収層１４の上にバッファー層１５ａ，ｂを堆積する。
バッファー層１５ａの成膜方法としては、真空プロセスのスパッタ法、真空蒸着法或いは有機金属気相成長（ＭＯＣＶＤ）、液相プロセスの化学析出（ＣＢＤ）法などが挙げられる。
バッファー層１５ｂの成膜方法としては、真空プロセスのスパッタ法、真空蒸着法或いは有機金属気相成長（ＭＯＣＶＤ）などが挙げられる。
[Step of depositing buffer layer on light absorption layer]
Buffer layers 15 a and 15 b are deposited on the obtained light absorption layer 14.
Examples of the method for forming the buffer layer 15a include a vacuum process sputtering method, a vacuum deposition method or metal organic chemical vapor deposition (MOCVD), and a liquid phase chemical deposition (CBD) method.
Examples of the method for forming the buffer layer 15b include sputtering in a vacuum process, vacuum deposition, or metal organic chemical vapor deposition (MOCVD).
［バッファー層上に透明電極を成膜する工程］
続いて、バッファー層１５ｂ上に、透明電極１６を堆積する。
成膜方法としては真空プロセスのスパッタ法、真空蒸着法或いは有機金属気相成長（ＭＯＣＶＤ）などが挙げられる。
[Step of depositing transparent electrode on buffer layer]
Subsequently, the transparent electrode 16 is deposited on the buffer layer 15b.
Examples of the film forming method include sputtering in a vacuum process, vacuum vapor deposition, or metal organic chemical vapor deposition (MOCVD).
［裏面電極上と透明電極上に取り出し電極を成膜する工程］
第１の取り出し電極１３を裏面電極１２上の光吸収層が成膜された部位を少なくとも除く部位に堆積する。
第２の取り出し電極１７を透明電極１６上の反射防止膜が成膜される部位を少なくとも除く部位に堆積する。
成膜方法としてはスパッタ法、真空蒸着法などが挙げられる。
第１と第２の取り出し電極の成膜は、１工程で行ってもよいし、それぞれ、別の工程として、任意の工程の後に行ってもよい。
[Step of taking out electrode film on back electrode and transparent electrode]
The first extraction electrode 13 is deposited on a portion excluding at least the portion where the light absorption layer is formed on the back electrode 12.
The second extraction electrode 17 is deposited on a portion excluding at least a portion where the antireflection film is formed on the transparent electrode 16.
Examples of the film forming method include a sputtering method and a vacuum deposition method.
The film formation of the first and second extraction electrodes may be performed in one step, or may be performed after any step as a separate step.
［透明電極上に反射防止膜を成膜する工程］
最後に透明電極１６上の第２の取り出し電極１７が成膜された部位を少なくとも除く部位に反射防止膜１８を堆積する。
成膜方法としてはスパッタ法、真空蒸着法などが挙げられる。
上記の工程を経て、図１の概念図に示した光電変換素子を作製する。
光電変換素子のモジュールを作製する場合、基板に裏面電極を成膜する工程の後、レーザーにより裏面電極を分断する工程、さらには光吸収層上にバッファー層を成膜する工程及びバッファー層上に透明電極を成膜する工程の後、それぞれメカニカルスクライブにより試料を分割する工程を挟むことにより集積化が可能となる。
以下、実施例により、本発明を詳細に説明する。
[Step of depositing antireflection film on transparent electrode]
Finally, an antireflection film 18 is deposited on the transparent electrode 16 at least on the part excluding the part where the second extraction electrode 17 is formed.
Examples of the film forming method include a sputtering method and a vacuum deposition method.
Through the above steps, the photoelectric conversion element shown in the conceptual diagram of FIG. 1 is manufactured.
When producing a module of a photoelectric conversion element, after the step of forming the back electrode on the substrate, the step of dividing the back electrode with a laser, the step of forming a buffer layer on the light absorption layer, and the buffer layer After the step of forming the transparent electrode, integration can be performed by sandwiching a step of dividing the sample by mechanical scribing.
Hereinafter, the present invention will be described in detail by way of examples.
（実施例１）
基板１１として青板ガラス基板を用い、スパッタ法により裏面電極１２となるＭｏ薄膜を７００ｎｍ程度堆積した。スパッタは、Ｍｏをターゲットとし、Ａｒガス雰囲気中でＲＦで２００Ｗ印加することにより行った。
裏面電極１２となるＭｏ薄膜堆積後、光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜を２μｍ程度堆積した。成膜中の基板温度は５５０℃とした。Ｃｕ、Ｉｎ及びＴｅのターゲットを用い、三元同時スパッタで成膜を行った。Ａｒガス雰囲気中でＣｕターゲット用のＲＦ出力を２００Ｗから１００Ｗに単調に変化させ、その他の二つのターゲットの出力は２００Ｗに固定した。
得られた光吸収層１４の上にバッファー層１５ａとしてＭｇを添加したＺｎＯ薄膜を５０ｎｍ程度堆積した。成膜はＲＦスパッタを用いたが、界面でのプラズマダメージを考慮して、５０Ｗの出力で行った。このバッファー層１５ａ上にバッファー層１５ｂとして、ＺｎＯ薄膜を堆積し、続いて、透明電極１６となるアルミナ（Ａｌ２Ｏ３）を２ｗｔ％含有するＺｎＯ：Ａｌを１μｍ程度堆積した。取り出し電極１３、１７として、Ａｌを蒸着法にて堆積した。膜厚はそれぞれ１００ｎｍ及び３００ｎｍとした。最後に反射防止膜１８としてＭｇＦ２をスパッタ法により堆積することにより、光吸収層のＩｎ／Ｃｕ比が裏面電極側から単調に増加した光電変換素子を得た。
Example 1
A blue glass substrate was used as the substrate 11, and a Mo thin film serving as the back electrode 12 was deposited by about 700 nm by sputtering. Sputtering was performed by applying 200 W by RF in an Ar gas atmosphere using Mo as a target.
After the Mo thin film to be the back electrode 12 was deposited, a Cu—In—Te thin film to be the light absorption layer 14 was deposited to about 2 μm. The substrate temperature during film formation was 550 ° C. Film formation was performed by ternary simultaneous sputtering using Cu, In, and Te targets. The RF output for the Cu target was monotonously changed from 200 W to 100 W in an Ar gas atmosphere, and the outputs of the other two targets were fixed at 200 W.
A ZnO thin film to which Mg was added as a buffer layer 15a was deposited on the obtained light absorption layer 14 to a thickness of about 50 nm. The film formation was performed by RF sputtering, but was performed at an output of 50 W in consideration of plasma damage at the interface. A ZnO thin film was deposited as a buffer layer 15b on the buffer layer 15a, and then ZnO: Al containing 2 wt% of alumina (Al 2 O 3 ) to be the transparent electrode 16 was deposited to a thickness of about 1 μm. As the extraction electrodes 13 and 17, Al was deposited by an evaporation method. The film thickness was 100 nm and 300 nm, respectively. Finally, MgF 2 was deposited as the antireflection film 18 by sputtering to obtain a photoelectric conversion element in which the In / Cu ratio of the light absorption layer increased monotonously from the back electrode side.
ソーラーシミュレータによりＡＭ１．５の擬似太陽光照射下で、電圧源とマルチメータを用い、電圧を印加しない時の電流を測定して短絡電流密度（Ｊｓｃ）を得た。 A short-circuit current density (Jsc) was obtained by measuring a current when no voltage was applied using a voltage source and a multimeter under irradiation of AM1.5 simulated sunlight by a solar simulator.
（実施例２）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、ＲＦ出力を下げる過程を１０回行うこと以外は実施例１と同じ方法で光電変換素子を製造した。
(Example 2)
In the process of changing the RF output for the Cu target from 200 W to 100 W in the formation of the Cu—In—Te thin film to be the light absorption layer 14, the same as Example 1 except that the process of decreasing the RF output is performed 10 times. The photoelectric conversion element was manufactured by the method.
（参考例１）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、ＲＦ出力を下げる過程を５回行うこと以外は実施例１と同じ方法で光電変換素子を製造した。
(Reference Example 1)
In the process of changing the RF output for the Cu target from 200 W to 100 W in the formation of the Cu—In—Te thin film to be the light absorption layer 14, the same as Example 1 except that the process of decreasing the RF output is performed five times. The photoelectric conversion element was manufactured by the method.
（参考例２）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、ＲＦ出力を下げる過程を３回行うこと以外は実施例１と同じ方法で光電変換素子を製造した。
(Reference Example 2)
In the process of changing the RF output for the Cu target from 200 W to 100 W in the formation of the Cu—In—Te thin film to be the light absorption layer 14, the process is the same as in Example 1 except that the process of decreasing the RF output is performed three times. The photoelectric conversion element was manufactured by the method.
（参考例３）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、ＲＦ出力を下げる過程を２回行うこと以外は実施例１と同じ方法で光電変換素子を製造した。
(Reference Example 3)
In the process of changing the RF output for the Cu target from 200 W to 100 W in the formation of the Cu—In—Te thin film to be the light absorption layer 14, the same as Example 1 except that the process of decreasing the RF output is performed twice. The photoelectric conversion element was manufactured by the method.
（比較例１）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、ＲＦ出力を下げる過程を１回だけ行うこと以外は実施例１と同じ方法で光電変換素子を製造した。
(Comparative Example 1)
In the process of changing the RF output for the Cu target from 200 W to 100 W in the formation of the Cu—In—Te thin film to be the light absorption layer 14, except that the process of decreasing the RF output is performed only once. The photoelectric conversion element was manufactured by the same method.
（比較例２）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗに固定すること以外は実施例１と同じ方法で光電変換素子を製造した。
(Comparative Example 2)
A photoelectric conversion element was manufactured in the same manner as in Example 1 except that the Cu-In-Te thin film serving as the light absorption layer 14 was formed and the RF output for the Cu target was fixed to 200 W.
（比較例３）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を１００Ｗに固定すること以外は実施例１と同じ方法で光電変換素子を製造した。
(Comparative Example 3)
A photoelectric conversion element was manufactured in the same manner as in Example 1 except that the Cu-In-Te thin film serving as the light absorption layer 14 was formed and the RF output for the Cu target was fixed to 100 W.
（比較例４）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を１００Ｗから２００Ｗまで単調に変化させること以外は実施例１と同じ方法で光電変換素子を製造した。
(Comparative Example 4)
A photoelectric conversion element was manufactured by the same method as in Example 1 except that the Cu output of the Cu target was monotonously changed from 100 W to 200 W in forming a Cu—In—Te thin film to be the light absorption layer 14.
（実施例３）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、成膜後半のＲＦ出力の変化速度を成膜前半のＲＦ出力の変化速度の２倍とすること以外は実施例１と同じ方法で光電変換素子を製造した。ｐ型光吸収層とｎ型化合物半導体層との界面でのｐ型光吸収層のＩＩＩｂ族/Ｃｕモル比をｘ１、ｐ型光吸収層の層厚の１／２でのＩＩＩｂ族/Ｃｕモル比をｘ２、裏面電極との界面でのＩＩＩｂ族/Ｃｕモル比をｘ３とした時、ｘ１＝２．８、ｘ２＝１．７、ｘ３＝１．１であった。
(Example 3)
In the process of changing the RF output for the Cu target from 200 W to 100 W in the formation of the Cu—In—Te thin film to be the light absorption layer 14, the change rate of the RF output in the latter half of the film formation is changed to the RF output in the first half of the film formation. A photoelectric conversion element was produced by the same method as in Example 1 except that the change rate was doubled. The group IIIb / Cu molar ratio of the p-type light absorbing layer at the interface between the p-type light absorbing layer and the n-type compound semiconductor layer is x1, and the group IIIb / Cu mole is 1/2 of the layer thickness of the p-type light absorbing layer. When the ratio was x2 and the group IIIb / Cu molar ratio at the interface with the back electrode was x3, x1 = 2.8, x2 = 1.7, and x3 = 1.1.
（実施例４）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、成膜後半のＲＦ出力の変化速度を成膜前半のＲＦ出力の変化速度の３倍とすること以外は実施例１と同じ方法で光電変換素子を製造した。ｐ型光吸収層とｎ型化合物半導体層との界面でのｐ型光吸収層のＩＩＩｂ族/Ｃｕモル比をｘ１、ｐ型光吸収層の層厚の１／２でのＩＩＩｂ族/Ｃｕモル比をｘ２、裏面電極との界面でのＩＩＩｂ族/Ｃｕモル比をｘ３とした時、ｘ１＝２．８、ｘ２＝１．６、ｘ３＝１．２であった。
Example 4
In the process of changing the RF output for the Cu target from 200 W to 100 W in the formation of the Cu—In—Te thin film to be the light absorption layer 14, the change rate of the RF output in the latter half of the film formation is changed to the RF output in the first half of the film formation. A photoelectric conversion element was produced by the same method as in Example 1 except that the rate of change was 3 times. The group IIIb / Cu molar ratio of the p-type light absorbing layer at the interface between the p-type light absorbing layer and the n-type compound semiconductor layer is x1, and the group IIIb / Cu mole is 1/2 of the layer thickness of the p-type light absorbing layer. When the ratio was x2 and the group IIIb / Cu molar ratio at the interface with the back electrode was x3, x1 = 2.8, x2 = 1.6, and x3 = 1.2.
（実施例５）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、成膜後半のＲＦ出力の変化速度を成膜前半のＲＦ出力の変化速度の５倍とすること以外は実施例１と同じ方法で光電変換素子を製造した。ｐ型光吸収層とｎ型化合物半導体層との界面でのｐ型光吸収層のＩＩＩｂ族/Ｃｕモル比をｘ１、ｐ型光吸収層の層厚の１／２でのＩＩＩｂ族/Ｃｕモル比をｘ２、裏面電極との界面でのＩＩＩｂ族/Ｃｕモル比をｘ３とした時、ｘ１＝２．９、ｘ２＝１．４、ｘ３＝１．１であった。
(Example 5)
In the process of changing the RF output for the Cu target from 200 W to 100 W in the formation of the Cu—In—Te thin film to be the light absorption layer 14, the change rate of the RF output in the latter half of the film formation is changed to the RF output in the first half of the film formation. A photoelectric conversion element was produced in the same manner as in Example 1 except that the rate of change was 5 times. The group IIIb / Cu molar ratio of the p-type light absorbing layer at the interface between the p-type light absorbing layer and the n-type compound semiconductor layer is x1, and the group IIIb / Cu mole is 1/2 of the layer thickness of the p-type light absorbing layer. When the ratio was x2 and the group IIIb / Cu molar ratio at the interface with the back electrode was x3, x1 = 2.9, x2 = 1.4, and x3 = 1.1.
（比較例５）
光吸収層１４となるＣｕ−Ｉｎ−Ｔｅ薄膜の成膜で、Ｃｕターゲット用のＲＦ出力を２００Ｗから１００Ｗまで変化させる過程で、成膜前半のＲＦ出力の変化速度を成膜後半のＲＦ出力の変化速度の２倍とすること以外は実施例１と同じ方法で光電変換素子を製造した。
(Comparative Example 5)
In the process of changing the RF output for the Cu target from 200 W to 100 W in the film formation of the Cu—In—Te thin film to be the light absorption layer 14, the change rate of the RF output in the first half of the film formation is changed to the RF output in the second half of the film formation. A photoelectric conversion element was produced by the same method as in Example 1 except that the change rate was doubled.
図７に実施例１から５、参考例１から３及び比較例１から５でＣｕ−Ｉｎ−Ｔｅ薄膜を成膜したときの膜厚方向のＶＢＭの形状を示す。図中の◎、○、△、×は、短絡電流密度の良し悪しを示す。◎から×に向けて、短絡電流密度が低下する。 FIG. 7 shows the shape of the VBM in the film thickness direction when Cu—In—Te thin films were formed in Examples 1 to 5, Reference Examples 1 to 3 and Comparative Examples 1 to 5. In the figure, ◎, ○, Δ, × indicate whether the short-circuit current density is good or bad. From ◎ to ×, the short circuit current density decreases.
実施例１、２参考例１〜３では、ＶＢＭの傾斜部が２箇所以上あり、キャリア（ホール）の移動度を早くし、キャリアの再結合を抑制する効果があるが、比較例１では、ＶＢＭの傾斜部が１箇所しかなく、キャリア（ホール）移動が不十分である。
光励起により生成されたキャリア（ホール）は、ｐｎ接合界面側から裏面電極側へ移動する。その時、ＶＢＭは右肩上がりに変化することが望ましい。実施例１では、ＶＢＭが右肩上がりに変化しているのに対し、比較例４では、ＶＢＭは逆向きに変化しており、キャリア（ホール）の移動を妨げるため好ましくない。比較例２及び３では、ＶＢＭは変化せず、キャリア（ホール）の移動度が低いため、再結合確率が増大するため好ましくない。
実施例３〜５では、界面再結合が起こりやすいｐｎ接合界面近傍からキャリア（ホール）を早く遠ざけることができるＶＢＭの形状でより好ましい。一方、比較例５では、逆にｐｎ接合界面近傍でのキャリア（ホール）移動が遅いＶＢＭの形状となり、再結合確率が増大するため好ましくない。
本発明の光電変換素子を太陽電池に用いることにより、変換効率の高い太陽電池を得ることができる。
In Example 1 and 2 Reference Examples 1 to 3 , there are two or more inclined parts of the VBM, which has the effect of increasing the mobility of carriers (holes) and suppressing carrier recombination. In Comparative Example 1, There is only one inclined part of the VBM, and carrier (hole) movement is insufficient.
Carriers (holes) generated by photoexcitation move from the pn junction interface side to the back electrode side. At that time, it is desirable that the VBM changes to the right shoulder. In the first embodiment, the VBM changes in a way that rises to the right, whereas in the comparative example 4, the VBM changes in the opposite direction, which is not preferable because the movement of the carrier (hole) is hindered. In Comparative Examples 2 and 3, the VBM does not change, and the mobility of carriers (holes) is low, which is not preferable because the recombination probability increases.
In Examples 3 to 5 , it is more preferable to use a VBM shape that can quickly move carriers (holes) from the vicinity of the pn junction interface where interface recombination easily occurs. On the other hand, Comparative Example 5 is not preferable because the carrier (hole) movement in the vicinity of the pn junction interface is slow and the recombination probability increases.
By using the photoelectric conversion element of the present invention for a solar cell, a solar cell with high conversion efficiency can be obtained.
以上、本発明の実施形態を説明したが、本発明は上記実施形態そのままに限定解釈されるものではなく、実施段階ではその要旨を逸脱しない範囲で構成要素を変形して具体化できる。また、上記実施形態に開示されている複数の構成要素の適宜な組み合わせにより種々の発明を形成することができる。例えば、変形例の様に異なる実施形態にわたる構成要素を適宜組み合わせても良い The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, as in the modification, the constituent elements over different embodiments may be appropriately combined.
１０…光電変換素子、１１…基板、１２…裏面電極、１３…第１の取り出し電極、１４…光吸収層、１５ａ…バッファー層、１５b…バッファー層、１６…透明電極層、１７…第２の取り出し電極、１８…反射防止膜 DESCRIPTION OF SYMBOLS 10 ... Photoelectric conversion element, 11 ... Board | substrate, 12 ... Back electrode, 13 ... 1st extraction electrode, 14 ... Light absorption layer, 15a ... Buffer layer, 15b ... Buffer layer, 16 ... Transparent electrode layer, 17 ... 2nd Extraction electrode, 18 ... antireflection film
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