JP2020053668A - Solar cell, multi-junction type solar cell, solar cell module and photovoltaic power generation system - Google Patents
Solar cell, multi-junction type solar cell, solar cell module and photovoltaic power generation system Download PDFInfo
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- 238000010248 power generation Methods 0.000 title claims abstract description 18
- 238000006243 chemical reaction Methods 0.000 claims abstract description 109
- 238000000103 photoluminescence spectrum Methods 0.000 claims abstract description 13
- BERDEBHAJNAUOM-UHFFFAOYSA-N copper(I) oxide Inorganic materials [Cu]O[Cu] BERDEBHAJNAUOM-UHFFFAOYSA-N 0.000 claims description 46
- 229940112669 cuprous oxide Drugs 0.000 claims description 46
- KRFJLUBVMFXRPN-UHFFFAOYSA-N cuprous oxide Chemical compound [O-2].[Cu+].[Cu+] KRFJLUBVMFXRPN-UHFFFAOYSA-N 0.000 claims description 38
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 claims description 18
- 239000010408 film Substances 0.000 description 40
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- 238000000034 method Methods 0.000 description 22
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 17
- 239000001301 oxygen Substances 0.000 description 17
- 229910052760 oxygen Inorganic materials 0.000 description 17
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 16
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 15
- 229910052751 metal Inorganic materials 0.000 description 15
- 239000002184 metal Substances 0.000 description 15
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 13
- 230000000052 comparative effect Effects 0.000 description 13
- 239000010949 copper Substances 0.000 description 13
- 239000005751 Copper oxide Substances 0.000 description 12
- 230000015572 biosynthetic process Effects 0.000 description 12
- 229910052802 copper Inorganic materials 0.000 description 12
- 229910000431 copper oxide Inorganic materials 0.000 description 12
- 229960004643 cupric oxide Drugs 0.000 description 12
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 12
- 229910001887 tin oxide Inorganic materials 0.000 description 12
- 238000004544 sputter deposition Methods 0.000 description 11
- -1 cuprous oxide compound Chemical class 0.000 description 8
- 230000006798 recombination Effects 0.000 description 8
- 239000011787 zinc oxide Substances 0.000 description 8
- 239000000969 carrier Substances 0.000 description 7
- 150000001875 compounds Chemical class 0.000 description 7
- 238000000151 deposition Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 238000005215 recombination Methods 0.000 description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
- 229910006404 SnO 2 Inorganic materials 0.000 description 6
- 238000003860 storage Methods 0.000 description 6
- 239000010409 thin film Substances 0.000 description 6
- 239000007789 gas Substances 0.000 description 5
- 239000004065 semiconductor Substances 0.000 description 5
- 229910052715 tantalum Inorganic materials 0.000 description 5
- 229910052721 tungsten Inorganic materials 0.000 description 5
- 238000012935 Averaging Methods 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 230000010354 integration Effects 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- 238000002834 transmittance Methods 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 3
- 230000005284 excitation Effects 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 229910003437 indium oxide Inorganic materials 0.000 description 3
- PJXISJQVUVHSOJ-UHFFFAOYSA-N indium(iii) oxide Chemical compound [O-2].[O-2].[O-2].[In+3].[In+3] PJXISJQVUVHSOJ-UHFFFAOYSA-N 0.000 description 3
- 238000005424 photoluminescence Methods 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 238000000992 sputter etching Methods 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- 239000011701 zinc Substances 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 2
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 2
- 229910005793 GeO 2 Inorganic materials 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 239000012298 atmosphere Substances 0.000 description 2
- 238000000231 atomic layer deposition Methods 0.000 description 2
- 238000000224 chemical solution deposition Methods 0.000 description 2
- 238000005229 chemical vapour deposition Methods 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 239000011889 copper foil Substances 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 229910001882 dioxygen Inorganic materials 0.000 description 2
- 238000005530 etching Methods 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 229910052733 gallium Inorganic materials 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- 230000031700 light absorption Effects 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 238000001420 photoelectron spectroscopy Methods 0.000 description 2
- 229910052709 silver Inorganic materials 0.000 description 2
- 230000003746 surface roughness Effects 0.000 description 2
- YVTHLONGBIQYBO-UHFFFAOYSA-N zinc indium(3+) oxygen(2-) Chemical compound [O--].[Zn++].[In+3] YVTHLONGBIQYBO-UHFFFAOYSA-N 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 229910004613 CdTe Inorganic materials 0.000 description 1
- 206010010957 Copper deficiency Diseases 0.000 description 1
- 206010021143 Hypoxia Diseases 0.000 description 1
- 239000004642 Polyimide Substances 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
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- 230000004888 barrier function Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- DVRDHUBQLOKMHZ-UHFFFAOYSA-N chalcopyrite Chemical group [S-2].[S-2].[Fe+2].[Cu+2] DVRDHUBQLOKMHZ-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 239000005345 chemically strengthened glass Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
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- 238000011109 contamination Methods 0.000 description 1
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- 239000002019 doping agent Substances 0.000 description 1
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- 238000004070 electrodeposition Methods 0.000 description 1
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- 230000002349 favourable effect Effects 0.000 description 1
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- 229910052731 fluorine Inorganic materials 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 125000005842 heteroatom Chemical group 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- AMGQUBHHOARCQH-UHFFFAOYSA-N indium;oxotin Chemical compound [In].[Sn]=O AMGQUBHHOARCQH-UHFFFAOYSA-N 0.000 description 1
- 238000002361 inverse photoelectron spectroscopy Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
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- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000007800 oxidant agent Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
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- 239000010453 quartz Substances 0.000 description 1
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- 229920005989 resin Polymers 0.000 description 1
- 238000001004 secondary ion mass spectrometry Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 239000005361 soda-lime glass Substances 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000005477 sputtering target Methods 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
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- 230000009466 transformation Effects 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
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- Photovoltaic Devices (AREA)
Abstract
Description
実施形態は太陽電池、多接合型太陽電池、太陽電池モジュール及び太陽光発電システムに関する。 Embodiments relate to a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system.
高効率な太陽電池として多接合型(タンデム)太陽電池がある。タンデム太陽電池は、波長帯毎に分光感度が高いセルを用いることができるため、単接合よりも高効率化できる。またタンデム太陽電池のトップセルとして、安価な材料でかつバンドギャップが広い亜酸化銅化合物が期待されている。しかし、これまでに銅箔を酸化させて作製した亜酸化銅太陽電池で８％程度の効率が報告されているが理論限界効率に比べると低い。これは銅箔を酸化させたのち最表面の酸化銅などの異相をエッチングして取り除いているが完全に除去できないこと及びエッチング溶液の構成元素が残るなどの理由で良好なｐｎ接合ができていないためと考えられる。また、この方法では0.1mm程度の厚さの箔を酸化させたのち20μｍ程度まで研磨する必要があり、大面積化が困難である。 As a high-efficiency solar cell, there is a multi-junction (tandem) solar cell. Since a tandem solar cell can use a cell having high spectral sensitivity for each wavelength band, higher efficiency can be achieved than a single junction. In addition, as a top cell of a tandem solar cell, a cuprous oxide compound which is an inexpensive material and has a wide band gap is expected. However, an efficiency of about 8% has been reported so far in a cuprous oxide solar cell manufactured by oxidizing a copper foil, but it is lower than the theoretical limit efficiency. This is because a foreign phase such as copper oxide on the outermost surface is removed by etching after oxidizing the copper foil, but a good pn junction has not been formed because it cannot be completely removed and a constituent element of the etching solution remains. It is thought to be. Further, in this method, it is necessary to oxidize a foil having a thickness of about 0.1 mm and then polish the foil to about 20 μm, and it is difficult to increase the area.
一方、薄膜では液相中での反応を用いるなどの方法で作製した例があるが効率は最高でも４％程度である。その主たる原因は膜中に異相だけでなく溶液中に含まれる不純物が取り込まれ、それらが光励起キャリアの再結合中心になっているためと思われる。そのような薄膜では本来吸収しない600nm以上の波長の光も吸収してしまうためタンデム太陽電池のトップセルには使用できない。一般に不純物の混入が少ない薄膜を作製する方法としてスパッタリング法が良く知られておりこの方法で作製した報告例もあるが変換効率は１％以下であった。その原因は不純物の混入がなくても銅や酸化銅の異相が生じやすく純粋な亜酸化銅が容易に得られないためと考えられる。 On the other hand, there is an example in which a thin film is manufactured by a method using a reaction in a liquid phase, but the efficiency is at most about 4%. It is considered that the main reason is that not only the heterophase but also impurities contained in the solution are taken into the film, and these become the recombination centers of the photoexcited carriers. Such a thin film also absorbs light having a wavelength of 600 nm or more, which is not originally absorbed, and therefore cannot be used for a tandem solar cell top cell. In general, a sputtering method is well known as a method for producing a thin film with a small amount of impurities mixed therein, and there is a report example produced by this method, but the conversion efficiency was 1% or less. It is considered that the reason is that even if there is no contamination of impurities, a different phase of copper or copper oxide is likely to be generated, and pure cuprous oxide cannot be easily obtained.
実施形態は、変換効率を向上させた太陽電池、多接合型太陽電池、太陽電池モジュール及び太陽光発電システムを提供する。 Embodiments provide a solar cell, a multi-junction solar cell, a solar cell module, and a solar power generation system with improved conversion efficiency.
実施形態の太陽電池は、第１電極と、第２電極と、前記第１電極と前記第２電極の間に設けられる光電変換層とを備え、光電変換層を100K以下の温度でフォトルミネッセンススペクトルを測定した場合650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値である第１の最高値（A）が600nm以上650nm以下での発光強度の最高値である第２の最高値（B）の100倍以下（A≦100B）である。 The solar cell according to the embodiment includes a first electrode, a second electrode, and a photoelectric conversion layer provided between the first electrode and the second electrode. The photoluminescence layer has a photoluminescence spectrum at a temperature of 100 K or less. Is measured, the first maximum value (A) which is the highest value of the light emission intensity in the wavelength range of 650 nm to 1000 nm is the second highest value (the highest value of the light emission intensity at 600 nm to 650 nm). B) 100 times or less (A ≦ 100B).
（第１実施形態）
第１実施形態は、太陽電池に関する。図１に、第１実施形態の太陽電池１００の概念図を示す。図１に示すように、本実施形態に係る太陽電池１００は、基板１と、基板１上に第１電極２と、第１電極２上に光電変換層３と、光電変換層３上にｎ型層４と、ｎ型層４上に第２電極５と、を備える。第１電極２と光電変換層３との間やｎ型層４と第２電極５との間には、図示しない中間層が含まれていてもよい。
(1st Embodiment)
The first embodiment relates to a solar cell. FIG. 1 shows a conceptual diagram of the solar cell 100 of the first embodiment. As shown in FIG. 1, the solar cell 100 according to the present embodiment includes a substrate 1, a first electrode 2 on the substrate 1, a photoelectric conversion layer 3 on the first electrode 2, and n on the photoelectric conversion layer 3. A mold layer; and a second electrode on the n-type layer. An intermediate layer (not shown) may be included between the first electrode 2 and the photoelectric conversion layer 3 or between the n-type layer 4 and the second electrode 5.
（基板）
実施形態の基板１としては、白板ガラスを用いることが望ましく、石英、ソーダライムガラス、化学強化ガラスなどガラス全般、ステンレス（ＳＵＳ）、Ｗ、Ｔａ、Ａｌ、Ｔｉ又はＣｒ等の金属板あるいはポリイミド、アクリル等の樹脂を用いることもできる。
(substrate)
As the substrate 1 of the embodiment, it is desirable to use white plate glass, and it is preferable to use glass such as quartz, soda lime glass, and chemically strengthened glass in general, stainless steel (SUS), a metal plate such as W, Ta, Al, Ti, or Cr, or polyimide; A resin such as acrylic can also be used.
（第１電極）
実施形態の第１電極２は、基板１と光電変換層３の間に存在する層である。図１では、第１電極２は、基板１と光電変換層３と直接接している。第１電極２としては、透明導電膜、金属膜と透明導電膜と金属膜を積層したものが好ましい。透明導電膜としては、酸化インジウムスズ（Indium Tin Oxide: ＩＴＯ）、アルミニウムドープ酸化亜鉛(Al-doped Zinc Oxide: AZO)、ボロンドープ酸化亜鉛（Boron-doped Zinc Oxide: BZO）、ガリウムドープ酸化亜鉛(Gallium-doped Zinc Oxide: GZO)、フッ素ドープ酸化スズ（Fluorine-doped Tin Oxide: FTO）、アンチモンドープ酸化スズ（Antimony-doped Tin Oxide: ATO）、チタンドープ酸化インジウム（Titanium-doped Indium Oxide: ITiO）、酸化インジウム酸化亜鉛(Indium Zinc Oxide: IZO)や酸化インジウムガリウム亜鉛（Indium Gallium Zinc Oxide: IGZO）、タンタルドープ酸化スズ（Ta-doped Tin Oxide: ＳｎＯ２：Ｔａ）、ニオブドープ酸化スズ（Nb-doped Tin Oxide: SnO2：Ｎｂ）、タングステンドープ酸化スズ（W-doped Tin Oxide: ＳｎＯ２：Ｗ）、モリブデンドープ酸化スズ（Mo-doped Tin Oxide: SnO2：Ｍｏ）、フッ素ドープ酸化スズ（F-doped Tin Oxide：SnO2:F）、水素ドープ酸化インジウム（Hydrogen-doped Indium Oxide：IOH）など特に限定されない。透明導電膜は、複数の膜を持つ積層膜であってもよく、上記酸化物の他に酸化スズなどの膜が積層膜に含まれていてもよい。酸化スズなどの膜へのドーパントとしては、Ｉｎ，Ｓｉ，Ｇｅ，Ｔｉ，銅，Ｓｂ，Ｎｂ，Ｆ，Ｔａ，Ｗ，Ｍｏ，Ｆ，Ｃｌなど特に限定されない。金属膜としては、Ｍｏ、Ａｕ、Ｃｕ、Ａｇ、Ａｌ、ＴａやＷの膜など特に限定されない。また、第１電極２は、透明導電膜上にドット状、ライン状もしくはメッシュ状の金属を設けた電極でもよい。このとき、ドット状、ライン状もしくはメッシュ状の金属は、透明導電膜と光電変換層３の間や透明導電膜の光電変換層３とは反対側に配置される。ドット状、ライン状もしくはメッシュ状の金属は、透明導電膜に対して開口率が５０％以上であることが好ましい。ドット状、ライン状もしくはメッシュ状の金属は、Ｍｏ、Ａｕ、Ｃｕ、Ａｇ、Ａｌ、ＴａやＷなど特に限定されない。
(First electrode)
The first electrode 2 of the embodiment is a layer existing between the substrate 1 and the photoelectric conversion layer 3. In FIG. 1, the first electrode 2 is in direct contact with the substrate 1 and the photoelectric conversion layer 3. The first electrode 2 is preferably a transparent conductive film, or a laminate of a metal film, a transparent conductive film and a metal film. The transparent conductive film includes indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), and gallium-doped zinc oxide (Gallium). -doped Zinc Oxide: GZO), Fluorine-doped Tin Oxide (FTO), Antimony-doped Tin Oxide (ATO), Titanium-doped Indium Oxide (ITiO), Indium zinc oxide (Indium Zinc Oxide: IZO), indium gallium zinc oxide (IGO), tantalum-doped tin oxide (Ta-doped Tin Oxide: SnO 2 : Ta), niobium-doped tin oxide (Nb-doped Tin) Oxide: SnO 2 : Nb), tungsten-doped tin oxide (SnO 2 : W), molybdenum-doped tin oxide (Mo-doped Tin Oxide: SnO 2 : Mo), fluorine-doped There is no particular limitation on tin oxide (F-doped Tin Oxide: SnO 2 : F) and hydrogen-doped indium oxide (Hydrogen-doped Indium Oxide: IOH). The transparent conductive film may be a stacked film having a plurality of films, and a film such as tin oxide may be included in the stacked film in addition to the oxide. The dopant for the film such as tin oxide is not particularly limited, such as In, Si, Ge, Ti, copper, Sb, Nb, F, Ta, W, Mo, F, and Cl. The metal film is not particularly limited, such as a film of Mo, Au, Cu, Ag, Al, Ta, or W. Further, the first electrode 2 may be an electrode in which a dot-shaped, line-shaped, or mesh-shaped metal is provided on a transparent conductive film. At this time, the dot-shaped, line-shaped, or mesh-shaped metal is disposed between the transparent conductive film and the photoelectric conversion layer 3 or on the side of the transparent conductive film opposite to the photoelectric conversion layer 3. The dot, line or mesh metal preferably has an aperture ratio of 50% or more with respect to the transparent conductive film. The dot-shaped, line-shaped or mesh-shaped metal is not particularly limited, such as Mo, Au, Cu, Ag, Al, Ta or W.
また、第1電極には透明導電膜に代えて、金属基板を用いてもよい。金属基板には例えばW、Cr、Ti、Ta、Al、SUS（例えばSUS430）などを用いることができる。この金属基板の上に、後述する光電変換層を直接成膜しても良い。 Further, a metal substrate may be used for the first electrode instead of the transparent conductive film. For the metal substrate, for example, W, Cr, Ti, Ta, Al, SUS (for example, SUS430) can be used. A photoelectric conversion layer described later may be directly formed on the metal substrate.
（光電変換層）
実施形態の光電変換層３は、p型の化合物半導体層である。光電変換層は第１電極２とｎ型の化合物半導体層４の間に存在する層である。なお以降はｎ型の化合物半導体層をn型層と称する。図１では、光電変換層３は、第１電極１とｎ型層４と直接接している。光電変換層３は、亜酸化銅を含む層である。光電変換層３には亜酸化銅は、ノンドープあるいはドープされた亜酸化銅である。亜酸化銅の厚さは、一般的には、５００ｎｍ以上０．３ｍｍ以下であるがこれに限定されない。亜酸化銅は、カルコパイライト構造を有する化合物と比べて安価であるため太陽電池１００の低コスト化が可能である。また、亜酸化銅は、バンドギャップが約２．１ｅＶでありワイドバンドギャップである。本実施形態に係る太陽電池１００の光電変換層３のバンドギャップが広いと、Ｓｉなどのナローバンドギャップな光電変換層３を有する太陽電池をボトムセルとして用いて多接合化したときに、第1の実施形態に係る太陽電池１００はボトムセル側での発電に寄与する波長の透過性が高いため、ボトムセル側での発電量が高いという点で、第1の実施形態に係る太陽電池１００は好ましい。第1の実施形態に係る太陽電池１００を多接合型の太陽電池として用いる場合、第1の実施形態に係る太陽電池１００は、光入射側に設けられることが好ましい。
(Photoelectric conversion layer)
The photoelectric conversion layer 3 of the embodiment is a p-type compound semiconductor layer. The photoelectric conversion layer is a layer existing between the first electrode 2 and the n-type compound semiconductor layer 4. Hereinafter, the n-type compound semiconductor layer is referred to as an n-type layer. In FIG. 1, the photoelectric conversion layer 3 is in direct contact with the first electrode 1 and the n-type layer 4. The photoelectric conversion layer 3 is a layer containing cuprous oxide. The cuprous oxide in the photoelectric conversion layer 3 is non-doped or doped cuprous oxide. The thickness of the cuprous oxide is generally 500 nm or more and 0.3 mm or less, but is not limited thereto. Cuprous oxide is less expensive than a compound having a chalcopyrite structure, so that the cost of the solar cell 100 can be reduced. Cuprous oxide has a band gap of about 2.1 eV, which is a wide band gap. When the band gap of the photoelectric conversion layer 3 of the solar cell 100 according to the present embodiment is wide, the first embodiment is performed when the solar cell having the narrow band gap photoelectric conversion layer 3 of Si or the like is used as a bottom cell to form a multi-junction. The solar cell 100 according to the first embodiment is preferable in that the solar cell 100 according to the embodiment has high transmittance of wavelengths that contribute to power generation on the bottom cell side, and thus has a high power generation amount on the bottom cell side. When the solar cell 100 according to the first embodiment is used as a multi-junction solar cell, the solar cell 100 according to the first embodiment is preferably provided on the light incident side.
ここで、本実施形態にかかる太陽電池の備える光電変換層３の作製方法について説明する。 Here, a method for manufacturing the photoelectric conversion layer 3 included in the solar cell according to the present embodiment will be described.
光電変換層３はスパッタリングを用い作製する。まず、Ａｒと酸素の混合ガス中で純度が４Ｎ以上の無酸素銅のターゲットに高周波電源から例えば、ＲＦ電力を供給することで亜酸化銅の薄膜が得ることができる。ＲＦ電源の代わりにＤＣ電源など他の電力を供給しても構わない。このとき、電極、例えばスパッタする際の基板の上の少なくとも一部に酸化物が存在することで、亜酸化銅形成時の酸素と電極（成膜時の基板に相当）の反応を適度に抑制することができ、良好な結晶が得られやすい。例えば、透明導電性酸化物を用いると、電極として用いることができるため、構成が安易になる点で望ましい。そのため、電極の少なくとも一部には酸化物が存在するが好ましい。スパッタリングの際用いる電力は直流でも良い。尚、この際に基板を４００℃以上７００℃以下、好ましくは４５０℃以上５５０℃以下に加熱する。このようにして亜酸化銅薄膜を作製することができる。Ａｒと酸素の流量比によっては銅や酸化銅などの異相が形成されることがあり、銅、酸化銅の形成を抑えるために例えば、Ａｒ流量と酸素流量の比を調整する必要がある。なお、酸化銅とはCuOのことである。 The photoelectric conversion layer 3 is formed using sputtering. First, a thin film of cuprous oxide can be obtained by supplying, for example, RF power from a high-frequency power source to a target of oxygen-free copper having a purity of 4N or more in a mixed gas of Ar and oxygen. Other electric power such as a DC power supply may be supplied instead of the RF power supply. At this time, the reaction between oxygen and the electrode (corresponding to the substrate during film formation) during formation of cuprous oxide is appropriately suppressed due to the presence of an oxide on at least a part of the electrode, for example, the substrate during sputtering. And good crystals are easily obtained. For example, when a transparent conductive oxide is used, it can be used as an electrode, which is preferable in that the structure is simplified. Therefore, an oxide is preferably present in at least a part of the electrode. The power used for sputtering may be DC. At this time, the substrate is heated to 400 ° C to 700 ° C, preferably 450 ° C to 550 ° C. Thus, a cuprous oxide thin film can be manufactured. A different phase such as copper or copper oxide may be formed depending on the flow ratio of Ar and oxygen. For example, it is necessary to adjust the ratio of the Ar flow rate to the oxygen flow rate in order to suppress the formation of copper and copper oxide. Note that copper oxide is CuO.
なお、スパッタリングは減圧下での成膜なので、周りには酸素はほとんどなく、光電変換層３の成膜温度が高いと、金属は還元されやすくなる。そのため、亜酸化銅を作製するためには適度に酸化させる必要があるので、還元されやすい環境、つまり高温ほど酸化剤、つまり酸素を多くする必要がある。言い換えると温度が高い場合はより還元されやすい雰囲気下となるため酸素流量を多めにする必要がある。そのため、高い温度で光電変換層３を製膜する際には、酸素流量も上げることで、質の高い光電変換層３を得ることができる。 Note that since sputtering is performed under reduced pressure, there is almost no oxygen around, and when the film formation temperature of the photoelectric conversion layer 3 is high, the metal is easily reduced. Therefore, in order to prepare cuprous oxide, it is necessary to appropriately oxidize, and therefore, it is necessary to increase the amount of the oxidizing agent, that is, oxygen, in an environment where reduction is easy, that is, in a higher temperature. In other words, when the temperature is high, the atmosphere is more easily reduced, so that it is necessary to increase the oxygen flow rate. Therefore, when the photoelectric conversion layer 3 is formed at a high temperature, a high-quality photoelectric conversion layer 3 can be obtained by increasing the oxygen flow rate.
亜酸化銅を製膜する基板には、透過性を有するものを用いることが好ましい。透明性を有するものを用いることで、ワイドギャップであることを活かして亜酸化銅が吸収できない波長領域を光入射方向とは反対側で有効に使うことができるからである。 It is preferable to use a substrate having transparency for a substrate on which cuprous oxide is formed. This is because, by using a material having transparency, a wavelength region in which cuprous oxide cannot be absorbed can be effectively used on the side opposite to the light incident direction by utilizing the wide gap.
銅や酸化銅は本実施形態に係る太陽電池の備える光電変換層３では異相となるため、これら異相を低減した太陽電池を作製することで、太陽電池の効率を向上させることができる。 Copper and copper oxide have different phases in the photoelectric conversion layer 3 included in the solar cell according to the present embodiment. Therefore, by manufacturing a solar cell in which these different phases are reduced, the efficiency of the solar cell can be improved.
光電変換層３に含まれる異相は太陽電池の光電変換効率（変換効率とも称する）に大きく影響する。先述したように異相が存在することで、光励起キャリアの再結合中心となり変換効率を低下させることや、光電変換層３そのものの質を低下させることが挙げられる。これは銅由来のリーク等が生じ、フィルファクター（ＦＦ：形状因子）が悪くなるためである。酸化銅が含まれる場合は再結合を促進することなどによりセル特性全体に悪影響を及ぼすためである。また、意図しない波長域の光を吸収してしまうことにより、後述する多接合型太陽電池にした場合、ボトムセルの変換効率を低下させることにもつながる。 The hetero-phase included in the photoelectric conversion layer 3 greatly affects the photoelectric conversion efficiency (also referred to as conversion efficiency) of the solar cell. As described above, the presence of the hetero-phase serves as a recombination center for photoexcited carriers to lower the conversion efficiency and to lower the quality of the photoelectric conversion layer 3 itself. This is because copper-derived leaks and the like occur, and the fill factor (FF: shape factor) deteriorates. This is because, when copper oxide is contained, the overall cell characteristics are adversely affected by promoting recombination and the like. In addition, by absorbing light in an unintended wavelength range, in the case of a multi-junction solar cell to be described later, the conversion efficiency of the bottom cell is reduced.
太陽電池の光電変換層３に存在する異相を測定するため、Ｘ線回折法で分析し、光電変換層３に異相が検出されない場合でも、高い変換効率が得られるとは限らない。これは、Ｘ線回折法では測定できない異相が存在するためである。そのため、フォトルミネッセンス法（Photo Luminescence；ＰＬ法）を用いて作製した太陽電池のフォトルミネッセンススペクトルを測定する。 In order to measure a different phase existing in the photoelectric conversion layer 3 of the solar cell, analysis is performed by an X-ray diffraction method, and even when a different phase is not detected in the photoelectric conversion layer 3, high conversion efficiency is not always obtained. This is because there is a different phase that cannot be measured by the X-ray diffraction method. Therefore, a photoluminescence spectrum of a solar cell manufactured using a photoluminescence method (Photo Luminescence; PL method) is measured.
ＰＬ法とは、薄膜にバンドギャップ以上のエネルギーをもつ光を当て、２次発光を調べる分析方法である。そのため、ＰＬ法を用いることで、太陽電池の光電変換層３の膜質を調べることができる。光電変換層３の膜質が良好なほどピーク強度が高く測定される。フォトルミネッセンススペクトルを測定することで、太陽電池の光電変換層３の質、例えば異相、欠陥などを測定することができる。 The PL method is an analysis method in which light having energy equal to or greater than the band gap is applied to a thin film and secondary light emission is examined. Therefore, by using the PL method, the film quality of the photoelectric conversion layer 3 of the solar cell can be examined. The better the film quality of the photoelectric conversion layer 3 is, the higher the peak intensity is measured. By measuring the photoluminescence spectrum, the quality of the photoelectric conversion layer 3 of the solar cell, for example, a different phase, a defect, or the like can be measured.
PL強度比の測定には、まず、太陽電池の縦横それぞれ４等分にする。次にスクライブ部分を除き、光電変換層３が存在する部分のうち５カ所を測定点として選択し、それぞれのPL強度比を測定する。これら５カ所の測定点でのPL強度比を平均することで、平均PL強度比を求めることができる。この測定点の選択には、太陽電池を縦横それぞれ４等分した線の交点から、測定対象の太陽電池の縦、横の長さに対して５％以内の範囲から選択する。なお、測定範囲はスクライブの間隔よりも狭い範囲で行う。 In measuring the PL intensity ratio, first, the solar cell is divided into four equal parts vertically and horizontally. Next, excluding the scribe part, five points are selected as measurement points from among the parts where the photoelectric conversion layer 3 exists, and the respective PL intensity ratios are measured. By averaging the PL intensity ratios at these five measurement points, an average PL intensity ratio can be obtained. The measurement point is selected from a crossing point of a line obtained by dividing the solar cell vertically and horizontally into four equal portions within a range of 5% or less with respect to the length and width of the solar cell to be measured. The measurement is performed in a range narrower than the scribe interval.
PL強度比は亜酸化銅では、例えば５３２ｎｍの波長のレーザー光を用いることができる。過度に短波長のレーザー光を用いると光電変換層３以外からのシグナルを検出する可能性があるため光電変換層３のバンドギャップを多少上回る程度のエネルギーを持つ光源を用いることが望ましい。 With respect to the PL intensity ratio, for cuprous oxide, for example, a laser beam having a wavelength of 532 nm can be used. If a laser beam having an excessively short wavelength is used, a signal from a portion other than the photoelectric conversion layer 3 may be detected. Therefore, it is preferable to use a light source having an energy slightly larger than the band gap of the photoelectric conversion layer 3.
太陽電池は極低温でのフォトルミネッセンススペクトルにおいて650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値（A）が600nm以上650nm以下での発光強度の最高値（B）の100倍以下（A≦100B）であることが好ましい。650ｎｍ以降は亜酸化銅中の酸素欠損や銅欠損に起因するものであり、600nm以上650nm以下範囲は亜酸化銅のバンド端発光に起因するものである。そのため、650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値が600nm以上650nm以下での発光強度の最高値の100倍以下であることで、高い変換効率を達成できる。また、より好ましくは３０倍以下（A≦30B）である。650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値が600nm以上650nm以下での発光強度の最高値の３0倍以下であることで、より光励起キャリアの再結合を防ぐことができるため、より高い変換効率を達成することができるためである。さらにより好ましくは1.5倍以下（A≦1.5B）である。さらに異相が少ないため、さらに高い変換効率を達成することができ、光励起キャリアの再結合を防ぐことができるためである。650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値が600nm以上650nm以下での発光強度の最高値の100倍より大きいと、変換効率が減少するため好ましくない（A＞100B）。 In a solar cell, the maximum value (A) of the light emission intensity in the wavelength range of 650 nm to 1000 nm in the photoluminescence spectrum at a very low temperature is 100 times or less the maximum value (B) of the light emission intensity in the wavelength range of 600 nm to 650 nm ( A ≦ 100B) is preferable. The wavelengths of 650 nm and below are caused by oxygen deficiency and copper deficiency in the cuprous oxide, and the range of 600 nm to 650 nm is caused by band edge emission of the cuprous oxide. Therefore, high conversion efficiency can be achieved when the maximum value of the light emission intensity in the wavelength range from 650 nm to 1000 nm is 100 times or less the maximum value of the light emission intensity in the wavelength range of 600 nm to 650 nm. Further, it is more preferably 30 times or less (A ≦ 30B). Since the maximum value of the emission intensity in the wavelength range of greater than 650 nm and 1000 nm or less is 30 times or less the maximum value of the emission intensity at 600 nm or more and 650 nm or less, recombination of photoexcited carriers can be further prevented. This is because higher conversion efficiency can be achieved. It is even more preferably 1.5 times or less (A ≦ 1.5B). This is because, since there is less heterogeneous phase, higher conversion efficiency can be achieved, and recombination of photoexcited carriers can be prevented. If the maximum value of the light emission intensity in the wavelength range from 650 nm to 1000 nm is more than 100 times the maximum value of the light emission intensity in the range from 600 nm to 650 nm, the conversion efficiency decreases, which is not preferable (A> 100B).
太陽電池のフォトルミネッセンススペクトルの測定方法は次のとおりである。
PL強度比の測定には、まず、太陽電池の縦横それぞれ４等分にする。次にスクライブ部分を除き、光電変換層３が存在する部分のうち５カ所を測定点として選択し、それぞれのPL強度比を測定する。これら５カ所の測定点でのPL強度比を平均することで、平均PL強度比を求めることができる。この測定点の選択には、太陽電池を縦横それぞれ４等分した線の交点から、測定対象の太陽電池の縦、横の長さに対して５％以内の範囲から選択する。なお、測定範囲はスクライブの間隔よりも狭い範囲で行う。
The method for measuring the photoluminescence spectrum of the solar cell is as follows.
In measuring the PL intensity ratio, first, the solar cell is divided into four equal parts vertically and horizontally. Next, excluding the scribe part, five points are selected as measurement points from among the parts where the photoelectric conversion layer 3 exists, and the respective PL intensity ratios are measured. By averaging the PL intensity ratios at these five measurement points, an average PL intensity ratio can be obtained. The measurement point is selected from a crossing point of a line obtained by dividing the solar cell vertically and horizontally into four equal portions within a range of 5% or less with respect to the length and width of the solar cell to be measured. The measurement is performed in a range narrower than the scribe interval.
PL強度比は亜酸化銅では、５３２ｎｍの波長のレーザー光を用いることができる。過度に短波長のレーザー光を用いると光電変換層３以外からのシグナルを検出する可能性があるため光電変換層３のバンドギャップを多少上回る程度のエネルギーを持つ光源を用いることが望ましい。例えば、測定点を中心に、太陽電池を１ｃｍ２角程度に切断し、クライオスタットを用いて約１０Ｋまで冷却する。顕微フォトルミネッセンス測定装置、例えば堀場製作所製 型式：LabRAM-HR PL装置を用い、532nmのＹＡＧレーザー（励起光強度：0.2mW）を用いて光電変換層３に照射する。積算時間を５秒、積算回数を３回として測定を行う。ホール径は１00μｍ、対物レンズは１５倍のものを用いる。検出器にはＣＣＤを用いている。これで図２のようなフォトルミネッセンススペクトルを得ることができる。これら５カ所の測定点でのPL強度比を平均することで、平均PL強度比を求めることができる。 As for the PL intensity ratio, laser light having a wavelength of 532 nm can be used for cuprous oxide. If a laser beam having an excessively short wavelength is used, a signal from a portion other than the photoelectric conversion layer 3 may be detected. Therefore, it is preferable to use a light source having an energy slightly larger than the band gap of the photoelectric conversion layer 3. For example, the solar cell is cut into a square of about 1 cm 2 around the measurement point, and cooled to about 10 K using a cryostat. The photoelectric conversion layer 3 is irradiated with a 532 nm YAG laser (excitation light intensity: 0.2 mW) using a microphotoluminescence measuring device, for example, a model: LabRAM-HR PL device manufactured by Horiba, Ltd. The measurement is performed with the integration time set to 5 seconds and the integration count set to 3 times. The hole diameter is 100 μm, and the objective lens has a magnification of 15 times. A CCD is used as a detector. Thus, a photoluminescence spectrum as shown in FIG. 2 can be obtained. By averaging the PL intensity ratios at these five measurement points, an average PL intensity ratio can be obtained.
第１の実施形態に係る太陽電池の備える光電変換層３の構成元素をＸ線光電子分光分析法（X-ray Photoelectron Spectroscopy；ＸＰＳ）により測定すると、結合エネルギー値が930eV以上934eV以下の範囲に亜酸化銅のピークが存在する。XPSで光電変換層３を測定することにより得られる結合エネルギー値が930eV以上934eV以下の範囲に見られる亜酸化銅のピークは、金属銅を構成する０価の銅に由来すると考えられるＣｕ（０）ピークと、亜酸化銅（酸化第一銅）を構成する１価の銅に由来すると考えられるＣｕ（Ｉ）ピークと、酸化銅（酸化第二銅）を構成する２価の銅に由来するＣｕ（ＩＩ）ピークからなると考えられる。従って、異相が少ない光電変換層３をXPSで測定した場合、他のピークが現れず、亜酸化銅（酸化第一銅）に由来した（Ｉ）ピークが単一のピークとなった場合、ピークトップを中心にほぼ左右対称な形になる。 When the constituent elements of the photoelectric conversion layer 3 included in the solar cell according to the first embodiment are measured by X-ray Photoelectron Spectroscopy (XPS), the binding energy value is in the range of 930 eV to 934 eV. There is a peak for copper oxide. The peak of cuprous oxide whose binding energy value obtained by measuring the photoelectric conversion layer 3 by XPS is in the range of 930 eV to 934 eV is considered to be derived from zero-valent copper constituting metallic copper. ) Peak, Cu (I) peak considered to be derived from monovalent copper forming cuprous oxide (cuprous oxide), and divalent copper forming copper oxide (cupric oxide) It is thought to consist of a Cu (II) peak. Therefore, when the photoelectric conversion layer 3 having a small number of different phases is measured by XPS, no other peak appears and the peak (I) derived from cuprous oxide (cuprous oxide) becomes a single peak. It is almost symmetrical about the top.
図３はＸ線光電子分光分析法を用いた光電変換層３の測定方法概略図である。図３を用いて説明すると、まず、第1の実施形態に係る太陽電池の備える光電変換層３をＸＰＳで分析した際に、結合エネルギー値が930eV以上934eV以下の範囲に見られる亜酸化銅のピークにおいて、最も大きい値をとる点、つまり亜酸化銅のピークトップ６の値の２／３の値を通る水平直線７と亜酸化銅のピークとが交わる第１の交点８及び第２の交点９があり、ピークトップ６から前記水平直線７へおろした垂線１０と前記水平直線７とが交わる第３の交点１１があり、第１の交点８及び第３の交点１１の成す第1の長さ１２と第２の交点９及び第３の交点１１の成す第2の長さ１３の差を調べる。第1の長さ１２を便宜上L1とし、第2の長さ１３を便宜上L2とする。この測定を、透過率を測定するのと同様に設定した測定点で行う。具体的に述べると、太陽電池の縦横それぞれ４等分にする。次にスクライブ部分を除き、光電変換層３が存在する部分のうち５カ所を測定点として選択し、それぞれをXPSで測定する。これら５カ所それぞれの測定点で第1の長さ（L1）と第2の長さ（L2）の差の割合（L1−L2の差の絶対値／L1とL2のいずれか長いほう）を求める。L1とL2のいずれか長いほう、とは、例えばL1とL2を比較し、L1の方が長い場合、L1を分母に用いることである。この求めた差の割合を平均することで、差の割合の平均を求めることができる。この測定点の選択には、太陽電池を縦横それぞれ４等分した線の交点から、測定対象の太陽電池の縦、横の長さに対して５％以内の範囲から選択する。なお、測定範囲はスクライブの間隔よりも狭い範囲で行う。異相が少ないほど第1の長さと第2の長さの差が小さくなる。 FIG. 3 is a schematic diagram illustrating a method for measuring the photoelectric conversion layer 3 using X-ray photoelectron spectroscopy. Explaining with reference to FIG. 3, first, when the photoelectric conversion layer 3 included in the solar cell according to the first embodiment is analyzed by XPS, a cuprous oxide having a binding energy value in a range of 930 eV or more and 934 eV or less is used. The first point 8 and the second point of intersection of the point where the peak takes the largest value, that is, the horizontal straight line 7 passing through 2/3 of the value of the peak top 6 of cuprous oxide and the peak of cuprous oxide 9, there is a third intersection 11 at which a perpendicular 10 extending from the peak top 6 to the horizontal straight line 7 intersects with the horizontal straight line 7, and a first length formed by the first intersection 8 and the third intersection 11. The difference between the length 12 and the second length 13 formed by the second intersection 9 and the third intersection 11 is examined. The first length 12 is L1 for convenience and the second length 13 is L2 for convenience. This measurement is performed at measurement points set in the same manner as the measurement of the transmittance. More specifically, the length and width of the solar cell are divided into four equal parts. Next, excluding the scribe part, five points are selected as measurement points from among the parts where the photoelectric conversion layer 3 exists, and each is measured by XPS. At each of these five measurement points, the ratio of the difference between the first length (L1) and the second length (L2) (the absolute value of the difference L1-L2 / L1 or L2, whichever is longer) is determined. . The longer one of L1 and L2 means that, for example, L1 and L2 are compared, and if L1 is longer, L1 is used as a denominator. By averaging the obtained difference ratios, an average of the difference ratios can be obtained. The measurement point is selected from a crossing point of a line obtained by dividing the solar cell vertically and horizontally into four equal portions within a range of 5% or less with respect to the length and width of the solar cell to be measured. The measurement is performed in a range narrower than the scribe interval. The smaller the number of different phases, the smaller the difference between the first length and the second length.
そのため、第１の交点８及び第３の交点１１の成す第1の長さ１２と第２の交点９及び第３の交点１１の成す第2の長さ１３の差の割合の平均が１５％以下であれば、光電変換層３に含まれる異相が十分少ないことを意味することができる。そのため、光励起キャリアの再結合の中心となり変換効率を低下させることや、光電変換層３そのものの質の低下を防ぐことができ、太陽電池の効率を向上させることができる。さらに、第１の交点８及び第３の交点１１の成す第1の長さ１２と第２の交点９及び第３の交点１１の成す第2の長さ１３の差の割合の平均が１０％以下の場合は、より光電変換層３に含まれる異相を少なくすることを示しているため、より太陽電池の効率を向上させることができる。 Therefore, the average of the ratio of the difference between the first length 12 formed by the first intersection 8 and the third intersection 11 and the second length 13 formed by the second intersection 9 and the third intersection 11 is 15%. If it is below, it can mean that the hetero phase included in the photoelectric conversion layer 3 is sufficiently small. Therefore, it becomes the center of the recombination of the photoexcited carriers, and the conversion efficiency can be reduced. Further, the quality of the photoelectric conversion layer 3 itself can be prevented from being lowered, and the efficiency of the solar cell can be improved. Furthermore, the average of the ratio of the difference between the first length 12 formed by the first intersection 8 and the third intersection 11 and the second length 13 formed by the second intersection 9 and the third intersection 11 is 10%. The following cases indicate that the number of different phases contained in the photoelectric conversion layer 3 is further reduced, so that the efficiency of the solar cell can be further improved.
なお、上述のように光電変換層３についてＸＰＳにより測定する際には、光電変換層３内部の状態を分析できるように、光電変換層３上のｎ型層や、その上にある後述する第２電極５を、Ａｒイオンエッチング等により除去してから測定することが好ましい。 When measuring the photoelectric conversion layer 3 by the XPS as described above, the n-type layer on the photoelectric conversion layer 3 and the n-type layer on the n It is preferable to measure after removing the two electrodes 5 by Ar ion etching or the like.
（ｎ型層）
ｎ型層４は、光電変換層３と第２電極５との間に存在する層である。図１では、ｎ型層４は、光電変換層３と第２電極５と直接接している。
(N-type layer)
The n-type layer 4 is a layer existing between the photoelectric conversion layer 3 and the second electrode 5. In FIG. 1, the n-type layer 4 is in direct contact with the photoelectric conversion layer 3 and the second electrode 5.
光電変換層３上に作製するｎ型層４は、作製の際に過剰な酸素が存在しないことが望ましい。これは、ｎ型層４に酸素が存在することで、亜酸化銅とｎ型層４の界面においてｎ型層４が含む酸素と亜酸化銅が反応し、酸化銅などの異相を生じることがある。この異相はｎ型層４に酸素が多く含まれているほど生じやすくなる。そのため、ｎ型層４には作製の際に過剰な酸素が存在しないことが望ましい。ｎ層はバッファー層などを含む複数の層から構成されていても良い。ｎ型層４の作製では、例えば、ｎ型層４はZnOとGeO2のスパッタリングターゲットをＡｒ気流中でco-sputterすることで作製できる。 The n-type layer 4 formed on the photoelectric conversion layer 3 desirably does not contain excessive oxygen during the preparation. This is because the presence of oxygen in the n-type layer 4 may cause the oxygen contained in the n-type layer 4 to react with the cuprous oxide at the interface between the cuprous oxide and the n-type layer 4 to generate a different phase such as copper oxide. is there. This different phase is more likely to occur as the n-type layer 4 contains more oxygen. Therefore, it is desirable that excess oxygen does not exist in the n-type layer 4 during fabrication. The n-layer may be composed of a plurality of layers including a buffer layer and the like. In the production of the n-type layer 4, for example, the n-type layer 4 can be produced by co-sputtering a sputtering target of ZnO and GeO 2 in an Ar gas flow.
ｎ型層４の厚さは、５ｎｍ以上１００ｎｍ以下であることが好ましい。ｎ型層４の厚さが５ｎｍ以下であるとｎ型層４のカバレッジが悪い場合にリーク電流が発生し、特性を低下させてしまう場合がある。ｎ型層４の厚さが１００ｎｍを超えるとｎ型層４の過度の高抵抗化による特性低下や、透過率低下による短絡電流低下が起こる場合がある。従って、ｎ型層４の厚さは１０ｎｍ以上５０ｎｍ以下がより好ましい。また、カバレッジの良い膜を実現するためにｎ型層４の表面粗さは５ｎｍ以下が好ましい。ｎ型層の質が高い場合は２００ｎｍ程度の膜厚でも動作する太陽電池が構成できる。 The thickness of the n-type layer 4 is preferably 5 nm or more and 100 nm or less. If the thickness of the n-type layer 4 is 5 nm or less, a leak current may be generated when the coverage of the n-type layer 4 is poor, and the characteristics may be degraded. If the thickness of the n-type layer 4 exceeds 100 nm, the characteristics may be deteriorated due to the excessive increase in the resistance of the n-type layer 4, or the short-circuit current may be reduced due to the decrease in the transmittance. Therefore, the thickness of the n-type layer 4 is more preferably 10 nm or more and 50 nm or less. Further, in order to realize a film having good coverage, the surface roughness of the n-type layer 4 is preferably 5 nm or less. When the quality of the n-type layer is high, a solar cell that operates even with a thickness of about 200 nm can be configured.
光電変換層３の伝導帯下端（Conduction Band Minimum: CBM）の位置（Ｅｃｐ（ｅＶ））とｎ型層４の伝導帯下の位置（Ｅｃｎ（ｅＶ））の差である伝導帯オフセット（ΔＥ＝Ｅｃｐ−Ｅｃｎ）は、−０．２ｅＶ以上０．６ｅＶ以下（−０．２ｅＶ≦ΔＥ≦＋０．６ｅＶ）であることが好ましい。伝導帯オフセットが０より大きいとｐｎ接合界面の伝導帯が不連続となりスパイクが生じる。伝導帯オフセットが０より小さいとｐｎ接合界面の伝導帯が不連続となりクリフが生じる。スパイク及びクリフはどちらも光生成電子の障壁となるため小さい方が好ましい。従って、伝導帯オフセットは、０．０ｅＶ以上０．４ｅＶ以下（０．０ｅＶ≦ΔＥ≦＋０．４ｅＶ）であることがより好ましい。ただし、ギャップ内準位を利用して伝導する場合はこの限りではない。ＣＢＭの位置は、以下の手法を用いて見積もることができる。電子占有準位の評価法である光電子分光により価電子帯上端（Valence Band Maximum: VBM）を実測し、続いて測定対象の材料のバンドギャップを仮定してＣＢＭを算出する。しかしながら、実際のｐｎ接合界面では、相互拡散や陽イオンの空孔発生など理想的な界面を維持していないため、バンドギャップが変化する可能性が高い。このため、ＣＢＭも直接的に光電子放出の逆過程を利用する逆光電子分光により評価することが好ましい。具体的には、太陽電池表面を低エネルギーイオンエッチングと正・逆光電子分光測定の繰り返しにより、ｐｎ接合界面の電子状態を評価できる。 The conduction band offset (E cn (eV)), which is the difference between the position (E cp (eV)) of the conduction band lower end (Conduction Band Minimum: CBM) of the photoelectric conversion layer 3 and the position (E cn (eV)) below the conduction band of the n-type layer 4. ΔE = E cp −E cn ) is preferably −0.2 eV or more and 0.6 eV or less (−0.2 eV ≦ ΔE ≦ + 0.6 eV). If the conduction band offset is larger than 0, the conduction band at the pn junction interface becomes discontinuous and spikes occur. If the conduction band offset is smaller than 0, the conduction band at the pn junction interface becomes discontinuous, and a cliff occurs. Since both the spike and the cliff are barriers for photogenerated electrons, it is preferable that the spike and the cliff are small. Therefore, the conduction band offset is more preferably not less than 0.0 eV and not more than 0.4 eV (0.0 eV ≦ ΔE ≦ + 0.4 eV). However, this is not the case when conduction is performed using the level in the gap. The position of the CBM can be estimated using the following method. The valence band maximum (Valence Band Maximum: VBM) is actually measured by photoelectron spectroscopy, which is a method for evaluating the electron occupied level, and then the CBM is calculated assuming the band gap of the material to be measured. However, at an actual pn junction interface, an ideal interface such as interdiffusion and generation of cation vacancies is not maintained, so that the band gap is likely to change. For this reason, it is preferable that the CBM is also evaluated by inverse photoelectron spectroscopy using the reverse process of photoelectron emission directly. Specifically, the electronic state of the pn junction interface can be evaluated by repeating low energy ion etching and forward / reverse photoelectron spectroscopy on the surface of the solar cell.
（第２電極）
図１では、第２電極５は、ｎ型層４と直接接している。第２電極５としては、透明導電膜が好ましい。透明導電膜は、第１電極２と同様の材料を用いることが好ましい。
太陽電池１００の組成などは、Ｘ線光電子分光（X-ray Photoelectron Spectroscopy: XPS）及び二次イオン質量分析（Secondary Ion Mass Spectrometry; SIMS）によって求められる。また、各層の厚さや粒径は、太陽電池１００の断面を１０万倍で透過型電子顕微鏡（Transmission Electron Microscope: TEM）による観察を行えばよい。表面粗さは原子間力顕微鏡（Atomic Force Microscope; AFM）で観察を行えばよい。
(Second electrode)
In FIG. 1, the second electrode 5 is in direct contact with the n-type layer 4. As the second electrode 5, a transparent conductive film is preferable. It is preferable to use the same material as the first electrode 2 for the transparent conductive film.
The composition of the solar cell 100 and the like are determined by X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS). The thickness and the particle size of each layer may be obtained by observing the cross section of the solar cell 100 with a transmission electron microscope (TEM) at a magnification of 100,000. The surface roughness may be observed with an atomic force microscope (AFM).
（第３電極）
実施形態の第３電極は、光電変換素子１００の電極であって、第２電極５の上の光吸収層３側とは反対側に形成された金属膜である。第３電極としては、ＮｉやＡｌ等の導電性の金属膜を用いることができる。第３電極の膜厚は、例えば、２００ｎｍ以上２０００ｎｍ以下である。また、第２電極５の抵抗値が低く、直列抵抗成分が無視できるほどの場合等には、第３電極を省いても構わない。
(Third electrode)
The third electrode of the embodiment is an electrode of the photoelectric conversion element 100, and is a metal film formed on the second electrode 5 on the side opposite to the light absorbing layer 3 side. As the third electrode, a conductive metal film such as Ni or Al can be used. The thickness of the third electrode is, for example, not less than 200 nm and not more than 2000 nm. When the resistance value of the second electrode 5 is low and the series resistance component is negligible, the third electrode may be omitted.
（反射防止膜）
実施形態の反射防止膜は、光吸収層３へ光を導入しやすくするための膜であって、第２電極５６上又は第３電極上の光吸収層３側とは反対側に形成されている。反射防止膜としては、例えば、ＭｇＦ２やＳｉＯ２を用いることが望ましい。なお、実施形態において、反射防止膜を省くことができる。各層の屈折率に応じて膜厚を調整する必要があるが、７０〜１３０ｎｍ（好ましくは、８０〜１２０ｎｍ）程度蒸着することが好ましい。
(Anti-reflective coating)
The antireflection film of the embodiment is a film for facilitating the introduction of light into the light absorption layer 3 and is formed on the second electrode 56 or on the third electrode on the side opposite to the light absorption layer 3 side. I have. It is desirable to use, for example, MgF 2 or SiO 2 as the antireflection film. In the embodiment, the anti-reflection film can be omitted. Although it is necessary to adjust the film thickness in accordance with the refractive index of each layer, it is preferable to deposit about 70 to 130 nm (preferably 80 to 120 nm).
ここで、本実施形態にかかる太陽電池の作製方法について説明する。 Here, a method for manufacturing the solar cell according to the present embodiment will be described.
（作製方法）
図４に、本実施形態に係る太陽電池の製造方法のフローチャートを示す。
基板１の上に第１電極２２２となる材料をスパッタなどで製膜する。（Ｓ１）。次に真空装置へ導入し、真空引きを行う（Ｓ２）。真空条件下で光電変換層３３となる材料をスパッタなどで製膜する（Ｓ３）。光電変換層３を製膜後、ｎ型層を製膜する（Ｓ４）。その後、第２電極５となる材料をスパッタなどで製膜する（Ｓ５）。作製する際はスーパーストレート型でもサブストレート型でもよい。
(Production method)
FIG. 4 shows a flowchart of the method for manufacturing a solar cell according to the present embodiment.
A material for the first electrode 222 is formed on the substrate 1 by sputtering or the like. (S1). Next, it is introduced into a vacuum device and evacuated (S2). A material for the photoelectric conversion layer 33 is formed under vacuum conditions by sputtering or the like (S3). After forming the photoelectric conversion layer 3, an n-type layer is formed (S4). Thereafter, a material for forming the second electrode 5 is formed by sputtering or the like (S5). When manufacturing, a superstrate type or a substrate type may be used.
ｎ型層４の製造方法は、上記のみに限られない。例えば、ＣＢＤ（Chemical Bath Deposition）、ＣＶＤ（Chemical Vapor Deposition）、ＡＬＤ（Atomic Layer Deposition）、塗布法、電析法などが挙げられる。 The method for manufacturing the n-type layer 4 is not limited to the above. For example, there are CBD (Chemical Bath Deposition), CVD (Chemical Vapor Deposition), ALD (Atomic Layer Deposition), a coating method, an electrodeposition method, and the like.
本実施形態に係る太陽電池は、第１電極と、第２電極と、第１電極と第２電極の間に設けられる光電変換層とを備え、光電変換層を100K以下の温度でフォトルミネッセンススペクトルを測定した場合650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値である第１の最高値（A）が600nm以上650nm以下での発光強度の最高値である第２の最高値（B）の100倍以下（A≦100B）である。そのため、光励起キャリアの再結合中心となり変換効率を低下させることや、光電変換層そのものの質を低下させることを防ぎ、高効率な太陽電池とすることができる。 The solar cell according to the present embodiment includes a first electrode, a second electrode, and a photoelectric conversion layer provided between the first electrode and the second electrode, and a photoluminescence spectrum of the photoelectric conversion layer at a temperature of 100 K or less. Is measured, the first maximum value (A) which is the highest value of the light emission intensity in the wavelength range of 650 nm to 1000 nm is the second highest value (the highest value of the light emission intensity at 600 nm to 650 nm). B) 100 times or less (A ≦ 100B). Therefore, it is possible to prevent a reduction in conversion efficiency as a center of recombination of photoexcited carriers and a reduction in quality of the photoelectric conversion layer itself, and to provide a highly efficient solar cell.
（第２実施形態）
第２実施形態は、多接合型太陽電池に関する。図５に第２実施形態の多接合型太陽電池２００の断面概念図を示す。図５の多接合型太陽電池２００は、光入射側に第１実施形態の太陽電池（第１太陽電池）１００と、第２太陽電池２０１を有する。第２太陽電池２０１の光電変換層のバンドギャップは、第１実施形態の太陽電池１００の光電変換層３よりも小さいバンドギャップを有する。なお、実施形態の多接合型太陽電池は、３以上の太陽電池を接合させた太陽電池も含まれる。
(2nd Embodiment)
The second embodiment relates to a multi-junction solar cell. FIG. 5 is a conceptual cross-sectional view of the multi-junction solar cell 200 according to the second embodiment. The multi-junction solar cell 200 of FIG. 5 has the solar cell (first solar cell) 100 of the first embodiment and the second solar cell 201 on the light incident side. The band gap of the photoelectric conversion layer of the second solar cell 201 has a smaller band gap than that of the photoelectric conversion layer 3 of the solar cell 100 of the first embodiment. The multi-junction solar cell of the embodiment includes a solar cell in which three or more solar cells are joined.
第１実施形態の太陽電池１００の光電変換層３のバンドギャップが約２．０ｅＶであるため、第２太陽電池２０１の光電変換層のバンドギャップは、１．０ｅＶ以上１．４ｅＶ以下であることが好ましい。第２太陽電池２０１の光電変換層としては、Ｉｎの含有比率が高いＣＩＧＳ系、ＣＩＴ系及びＣｄＴｅ系、酸化銅系のうちのいずれか１種以上の化合物半導体層又は結晶シリコンであることが好ましい。 Since the band gap of the photoelectric conversion layer 3 of the solar cell 100 of the first embodiment is about 2.0 eV, the band gap of the photoelectric conversion layer of the second solar cell 201 is not less than 1.0 eV and not more than 1.4 eV. Is preferred. The photoelectric conversion layer of the second solar cell 201 is preferably a compound semiconductor layer of at least one of CIGS-based, CIT-based, CdTe-based, and copper oxide-based compounds having a high In content ratio or crystalline silicon. .
第１の実施形態に係る太陽電池を第１太陽電池とすることで、第１太陽電池での意図しない波長域の光を吸収してしまうことによりボトムセル（第２太陽電池）の変換効率を低下させることを防ぐことができるので、効率の良い多接合型太陽電池とすることができる。 By using the solar cell according to the first embodiment as the first solar cell, the conversion efficiency of the bottom cell (second solar cell) is reduced by absorbing light in an unintended wavelength range in the first solar cell. Therefore, an efficient multi-junction solar cell can be obtained.
（第３実施形態）
第３実施形態は、太陽電池モジュールに関する。図６に第３実施形態の太陽電池モジュール３００の斜視概念図を示す。図６の太陽電池モジュール３００は、第１太陽電池モジュール３０１と第２太陽電池モジュール３０２を積層した太陽電池モジュールである。第１太陽電池モジュール３０１は、光入射側であり、第１実施形態の太陽電池１００を用いている。第２の太陽電池モジュール３０２には、第２太陽電池２０１を用いることが好ましい。
(Third embodiment)
The third embodiment relates to a solar cell module. FIG. 6 is a perspective conceptual view of a solar cell module 300 according to the third embodiment. The solar cell module 300 in FIG. 6 is a solar cell module in which a first solar cell module 301 and a second solar cell module 302 are stacked. The first solar cell module 301 is on the light incident side, and uses the solar cell 100 of the first embodiment. It is preferable to use the second solar cell 201 for the second solar cell module 302.
図７に太陽電池モジュール３００の断面概念図を示す。図７では、第１太陽電池モジュール３０１の構造を詳細に示し、第２太陽電池モジュール３０２の構造は示していない。第２太陽電池モジュール３０２では、用いる太陽電池の光電変換層などに応じて適宜、太陽電池モジュールの構造を選択する。図７の太陽電池モジュールは、複数の太陽電池１００（太陽電池セル）が横方向に並んで電気的に直列に接続した破線で囲われたサブモジュール３０３が複数含まれ、複数のサブモジュール３０３が電気的に並列もしくは直列に接続している。 FIG. 7 shows a conceptual sectional view of the solar cell module 300. In FIG. 7, the structure of the first solar cell module 301 is shown in detail, and the structure of the second solar cell module 302 is not shown. In the second solar cell module 302, the structure of the solar cell module is appropriately selected according to the photoelectric conversion layer of the solar cell to be used. The solar cell module in FIG. 7 includes a plurality of submodules 303 surrounded by a broken line in which a plurality of solar cells 100 (solar cells) are arranged in a horizontal direction and electrically connected in series. They are electrically connected in parallel or in series.
太陽電池１００は、スクライブされていて、隣り合う太陽電池１００は、上部側の第２電極５と下部側の第１電極２が接続している。第３実施形態の太陽電池１００も第１実施形態の太陽電池１００と同様に、基板１、第１電極２、光電変換層３、ｎ型層４と第２電極５を有する。 The solar cell 100 is scribed, and the adjacent second solar cell 100 is connected to the upper second electrode 5 and the lower first electrode 2. The solar cell 100 according to the third embodiment also includes a substrate 1, a first electrode 2, a photoelectric conversion layer 3, an n-type layer 4, and a second electrode 5, similarly to the solar cell 100 according to the first embodiment.
モジュール毎に出力電圧が異なると電圧の低い部分に電流が逆流したり、余計な熱を発生させたりすることがあるためモジュールの出力低下につながる。 If the output voltage is different for each module, the current may flow backward to a low voltage portion or generate extra heat, which leads to a decrease in the output of the module.
また、本願の太陽電池を用いると各波長帯に適した太陽電池を用いることができるため、単体で用いたときと比較して効率良く発電できるようになり、モジュールの全体の出力が増大するため望ましい。 In addition, since the use of the solar cell of the present application makes it possible to use a solar cell suitable for each wavelength band, power can be generated more efficiently than when used alone, and the overall output of the module increases. desirable.
モジュール全体の変換効率が高いと、照射された光エネルギーのうち、熱になるエネルギー割合を低くすることができる。そのためモジュール全体の温度が上昇による効率の低下を抑制することができる。 If the conversion efficiency of the entire module is high, the proportion of the emitted light energy that becomes heat can be reduced. Therefore, a decrease in efficiency due to an increase in the temperature of the entire module can be suppressed.
（第４実施形態）
第４実施形態は太陽光発電システムに関する。第３実施形態の太陽電池モジュール３００は、第４実施形態の太陽光発電システムにおいて、発電を行う発電機として用いることができる。実施形態の太陽光発電システムは、太陽電池モジュールを用いて発電を行うものであって、具体的には、発電を行う太陽電池モジュールと、発電した電気を電力変換する手段と、発電した電気をためる蓄電手段又は発電した電気を消費する負荷とを有する。図８に実施形態の太陽光発電システム４００の構成概念図を示す。図８の太陽光発電システムは、太陽電池モジュール４０１（３００）と、コンバーター４０２と、蓄電池４０３と、負荷４０４とを有する。蓄電池４０３と負荷４０４は、どちらか一方を省略しても良い。負荷４０４は、蓄電池４０３に蓄えられた電気エネルギーを利用することもできる構成にしてもよい。コンバーター４０２は、ＤＣ−ＤＣコンバーター、ＤＣ−ＡＣコンバーター、ＡＣ−ＡＣコンバーターなど変圧や直流交流変換などの電力変換を行う回路又は素子を含む装置である。コンバーター４０２の構成は、発電電圧、蓄電池４０３や負荷４０４の構成に応じて好適な構成を採用すればよい。
(Fourth embodiment)
The fourth embodiment relates to a solar power generation system. The solar cell module 300 of the third embodiment can be used as a generator for generating power in the solar power generation system of the fourth embodiment. The photovoltaic power generation system of the embodiment generates power using a solar cell module, and specifically, a solar cell module that generates power, a unit that converts the generated power into power, and And a load that consumes generated electricity. FIG. 8 shows a conceptual configuration diagram of a photovoltaic power generation system 400 according to the embodiment. The solar power generation system in FIG. 8 includes a solar cell module 401 (300), a converter 402, a storage battery 403, and a load 404. Either the storage battery 403 or the load 404 may be omitted. The load 404 may be configured to be able to use the electric energy stored in the storage battery 403. The converter 402 is a device including a circuit or an element such as a DC-DC converter, a DC-AC converter, or an AC-AC converter that performs power conversion such as voltage transformation or DC-AC conversion. The configuration of the converter 402 may be a suitable configuration according to the configuration of the generated voltage, the storage battery 403, and the load 404.
太陽電池モジュール３００に含まれる受光したサブモジュール３０１に含まれる太陽電池セルが発電し、その電気エネルギーは、コンバーター４０２で変換され、蓄電池４０３で蓄えられるか、負荷４０４で消費される。太陽電池モジュール４０１には、太陽電池モジュール４０１を常に太陽に向けるための太陽光追尾駆動装置を設けたり、太陽光を集光する集光体を設けたり、発電効率を向上させるための装置等を付加することが好ましい。 A photovoltaic cell included in the sub-module 301 that receives light included in the solar cell module 300 generates power, and its electric energy is converted by the converter 402 and stored in the storage battery 403 or consumed by the load 404. The solar cell module 401 includes a solar tracking driving device for constantly directing the solar cell module 401 toward the sun, a light collector for condensing sunlight, a device for improving power generation efficiency, and the like. It is preferable to add.
太陽光発電システム４００は、住居、商業施設や工場などの不動産に用いられたり、車両、航空機や電子機器などの動産に用いられたりすることが好ましい。実施形態の変換効率に優れた太陽電池を太陽電池モジュール４０１に用いることで、発電量の増加が期待される。 The photovoltaic power generation system 400 is preferably used for real estate such as dwellings, commercial facilities, factories, and the like, or used for movable products such as vehicles, aircraft, and electronic devices. By using the solar cell having excellent conversion efficiency of the embodiment for the solar cell module 401, an increase in power generation is expected.
以下、実施例に基づき本発明をより具体的に説明するが、本発明は以下の実施例に限定されるものではない。 Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples.
［実施例］
トップセルを作製し、PL強度比、XPS値、変換効率を測定する。
[Example]
Prepare a top cell and measure the PL intensity ratio, XPS value, and conversion efficiency.
（実施例１）
白板ガラス基板上に、裏面側の第１電極としてITO透明導電膜、その上にＳｂドープしたＳｎＯ２透明導電膜を堆積する。透明な第１電極上に窒素及び酸素とアルゴンガスの割合（O2/(Ar+O2)比）が０．０７８の雰囲気中でスパッタリング法により４５０℃で加熱して亜酸化銅化合物を成膜する。その後、室温でスパッタリング法によりｐ−亜酸化銅層上にｎ型のＺｎ０．８Ｇｅ０．２Ｏｘを堆積し、その上に反射防止膜としてMgF2を堆積する。その後表面側の第２電極としてＡＺＯ透明導電膜を堆積する。また表面側の第２電極堆積時には亜酸化銅の酸化を抑制するため室温で成膜する必要があるが、例えばＡＺＯを用いる事により室温でも低抵抗な膜が得られる。ＡＺＯのターゲットは、ＺｎＯに対してＡｌ２Ｏ３の割合が２ｗｔ％から３ｗｔ％程度が好ましいが素子に対して十分低い抵抗値かつ高い透過率であればこの限りではない。
(Example 1)
On a white glass substrate, an ITO transparent conductive film is deposited as a backside first electrode, and an Sb-doped SnO 2 transparent conductive film is deposited thereon. The cuprous oxide compound was formed on the transparent first electrode by heating at 450 ° C. by sputtering in an atmosphere in which the ratio of nitrogen, oxygen and argon gas (O 2 / (Ar + O 2 ) ratio) was 0.078. Film. Then depositing an n-type Zn 0.8 Ge 0.2 O x in p- cuprous oxide layer by sputtering at room temperature, depositing MgF 2 as an anti-reflection film thereon. Thereafter, an AZO transparent conductive film is deposited as a second electrode on the surface side. When depositing the second electrode on the surface side, it is necessary to form a film at room temperature in order to suppress oxidation of cuprous oxide. For example, by using AZO, a film having low resistance can be obtained even at room temperature. The target of AZO is preferably such that the ratio of Al 2 O 3 to ZnO is about 2 wt% to 3 wt%, but this is not limited as long as it has a sufficiently low resistance value and high transmittance for the device.
PL強度比の測定方法は次のとおりである。 The method for measuring the PL intensity ratio is as follows.
太陽電池の縦横それぞれ４等分にし、太陽電池を縦横それぞれ４等分した線の交点を５カ所選ぶ。それぞれの交点から、測定対象の太陽電池の縦、横の長さに対して５％以内の範囲から測定点を選択し、それぞれのPL強度比を測定した。この測定点に対し、クライオスタットを用いて約１０Ｋまで冷却し、顕微フォトルミネッセンス測定装置（堀場製作所製 型式：LabRAM-HR PL装置）を用い、532nmのＹＡＧレーザー（励起光強度：0.2mW）を用いて光電変換層に照射した。照射では積算時間を５秒、積算回数を３回として測定した。ホール径は１00μｍ、対物レンズは１５倍のものを用いた。５カ所の測定点それぞれのPL強度比から、平均PL強度比を求め、表１に記載した。 Divide the solar cell vertically and horizontally into four equal parts, and select five intersections of the lines obtained by dividing the solar cell into four equal parts vertically and horizontally. From each intersection, a measurement point was selected from a range of 5% or less with respect to the vertical and horizontal lengths of the solar cell to be measured, and each PL intensity ratio was measured. The measurement point was cooled to about 10K using a cryostat, and a 532 nm YAG laser (excitation light intensity: 0.2 mW) was used using a microphotoluminescence measurement device (Model: LabRAM-HR PL manufactured by Horiba, Ltd.). To irradiate the photoelectric conversion layer. The irradiation was measured with an integration time of 5 seconds and an integration count of 3 times. The hole diameter was 100 μm, and the objective lens used was 15 times. The average PL intensity ratio was determined from the PL intensity ratio at each of the five measurement points, and is shown in Table 1.
XPS値の測定は次のように行った。 The measurement of the XPS value was performed as follows.
光電変換層のＸＰＳによる元素分析は、まず、太陽電池からArイオンエッチングを用いて第2電極及びｎ型層を除去し、光電変換層を露出させた。次に、露出した光電変換層に対し、下記の装置及び測定条件を用いて測定した。使用機器は、島津製作所 AXIS Ultra DLDを用い、励起源としてmonochro(Al-Kα)（１５ｋＶ×１５ｍＡ）を用いた。測定の際のモードは、Analyser modeはSpectrum、Lens ModeはHybridとした。また光電子取出し角は４５°で行い、取込領域を、Wide scanでは結合エネルギー値が0〜1200ｅＶの範囲、Narrow scanでは亜酸化銅のメインピークが見えるCu2pの926~942 eVの範囲、Ｃ１ｓの278〜294eVの範囲で行った。またこの際の、Pass Energy はWide scanで160 eV、Narrow scanで10 eVで行った。測定は結合エネルギー値が0.1eV刻みになるよう測定した。帯電補正は、表面汚染炭化水素のC1sピークを284.8 eVとして行った。このようにして光電変換層をXPSで５箇所測定し、それぞれの差の誤差範囲の平均を求めた。この結果も表1にまとめた。表１には差の割合の平均の範囲が１０％以内であれば◎、差の割合の平均の範囲が１５％以内であれば○とし、１５％より大きい場合は×と表記した。 In the elemental analysis of the photoelectric conversion layer by XPS, first, the second electrode and the n-type layer were removed from the solar cell by using Ar ion etching to expose the photoelectric conversion layer. Next, the exposed photoelectric conversion layer was measured using the following apparatus and measurement conditions. The instrument used was AXIS Ultra DLD, Shimadzu Corporation, and monochro (Al-Kα) (15 kV × 15 mA) was used as the excitation source. The mode at the time of measurement was set to Spectrum for Analyzer mode and Hybrid for Lens Mode. The photoelectron take-out angle is 45 °, and the take-in region has a binding energy value of 0 to 1200 eV in Wide scan, a 926 to 942 eV range of Cu2p in which a main peak of cuprous oxide can be seen in Narrow scan, and C1s. Performed in the range of 278-294 eV. In this case, Pass Energy was performed at 160 eV in the Wide scan and 10 eV in the Narrow scan. The measurement was performed so that the binding energy value was in steps of 0.1 eV. The charge correction was performed with the C1s peak of the surface-contaminated hydrocarbon set at 284.8 eV. In this way, the photoelectric conversion layer was measured at five points by XPS, and the average of error ranges of the respective differences was obtained. Table 1 also summarizes the results. In Table 1, ◎ indicates that the average range of the difference ratio is within 10%, ○ indicates that the average range of the difference ratio is within 15%, and X indicates that the average range is greater than 15%.
変換効率の測定方法は、以下の通りである。 The method for measuring the conversion efficiency is as follows.
ＡＭ１．５Ｇの光源を模擬したソーラーシミュレータを用い、その光源下で基準となるＳｉセルを用いて１ｓｕｎになるように光量を調節する。気温は２５℃。横軸を電圧、縦軸を電流密度とした際に、横軸と交わる点がＶｏｃとなり、電圧計でＶｏｃをカバーするような値（たとえば、１．６Ｖ）からＪｓｃが測定できる範囲（マイナス領域、たとえば−０．４Ｖ）まで電圧スイープを行い、その際の電流値を測定する。太陽電池の面積で除した値が電流密度（ｍＡ/ｃｍ２）となり、印加電圧が０Ｖでの電流密度の値がＪｓｃ(短絡電流密度)となる。
効率ηはη=Ｖｏｃ×Ｊｓｃ×ＦＦ/Ｐ×１００
Ｐは入射パワー密度、ＡＭ１．５の疑似太陽光を基準太陽電池セルで校正する。
ＦＦはＦＦ=Ｖｍｐｐ×Ｊｍｐｐ/（Ｖｏｃ×Ｊｓｃ）で求まる。Ｖｍｐｐ、ＪｍｐｐはＶ×Ｊの積が一番大きくなる点でのＶ、Ｊの値である。
Using a solar simulator simulating an AM1.5G light source, the light amount is adjusted to 1 sun using a reference Si cell under the light source. The temperature is 25 ° C. When the horizontal axis represents voltage and the vertical axis represents current density, the point at which the horizontal axis intersects is Voc, and a range in which Jsc can be measured from a value (eg, 1.6 V) that covers Voc with a voltmeter (minus region). , For example, -0.4 V), and the current value at that time is measured. The value obtained by dividing the area of the solar cell is the current density (mA / cm 2 ), and the value of the current density at an applied voltage of 0 V is Jsc (short-circuit current density).
The efficiency η is η = Voc × Jsc × FF / P × 100
P calibrates simulated sunlight having an incident power density of AM1.5 with a reference solar cell.
FF is obtained by FF = Vmpp × Jmpp / (Voc × Jsc). Vmpp and Jmpp are the values of V and J at the point where the product of V × J is the largest.
このとき、表１には、実施例１を基準として、他の実施例及び比較例の太陽電池効率（ＦＦ）を算出した。 At this time, in Table 1, the solar cell efficiencies (FF) of the other Examples and Comparative Examples were calculated based on Example 1.
後する実施例２〜６及び比較例１〜５についても測定の結果は表1にまとめた。 Table 1 also summarizes the measurement results of Examples 2 to 6 and Comparative Examples 1 to 5 described later.
（実施例２〜実施例6）
酸素とアルゴンガスの割合を表１記載の通りとした以外、実施例１と同様に作製、測定した。
(Examples 2 to 6)
Preparation and measurement were performed in the same manner as in Example 1 except that the ratios of oxygen and argon gas were as shown in Table 1.
(比較例１)
ｎ型を堆積する際に酸素気流が存在する以外実施例１と同様に作製、測定した。
(Comparative Example 1)
Production and measurement were performed in the same manner as in Example 1 except that an oxygen gas flow was present when n-type was deposited.
(比較例２)
ｎ型層を堆積する際にターゲットにZn＋Geを用いた以外、比較例１と同様に作製、測定した。
(Comparative Example 2)
Fabrication and measurement were performed in the same manner as in Comparative Example 1 except that Zn + Ge was used as the target when depositing the n-type layer.
(比較例３)
ｎ型層を堆積する際にターゲットにＺｎO＋Ｇｅを用いた以外、比較例１と同様に作製、測定した。
(Comparative Example 3)
Fabrication and measurement were performed in the same manner as in Comparative Example 1 except that ZnO + Ge was used as a target when depositing the n-type layer.
(比較例４)
ｎ型層を堆積する際にターゲットにＺｎ＋ＧｅO2を用いた以外、比較例１と同様に作製、測定した。
(Comparative Example 4)
Production and measurement were performed in the same manner as in Comparative Example 1, except that Zn + GeO 2 was used as a target when depositing the n-type layer.
（実施例７~実施例１２）
第1電極としてタングステン（W）を用い、酸素とアルゴンガスの割合を表２記載の通りとした以外、実施例１と同様に作製、測定した。
(Examples 7 to 12)
Production and measurement were performed in the same manner as in Example 1 except that tungsten (W) was used as the first electrode and the ratio of oxygen and argon gas was as shown in Table 2.
（実施例１３）
亜酸化銅を製膜する際に４００℃で行った以外実施例８と同様に作製、測定した。
(Example 13)
Production and measurement were performed in the same manner as in Example 8 except that the formation of cuprous oxide was performed at 400 ° C.
（実施例１４）
亜酸化銅化合物を製膜する際に６００℃で行った以外実施例９と同様に作製、測定した。
(Example 14)
It was prepared and measured in the same manner as in Example 9 except that the formation of the cuprous oxide compound was performed at 600 ° C.
（比較例５）
ｎ型を堆積する際に酸素気流が存在する以外実施例７と同様に作製、測定した。
(Comparative Example 5)
Production and measurement were performed in the same manner as in Example 7 except that an oxygen gas flow was present when depositing the n-type.
（実施例１５）
亜酸化銅化合物を製膜する際に４００℃で行った以外実施例１と同様に作製、測定した。
(Example 15)
Production and measurement were performed in the same manner as in Example 1 except that the formation of the cuprous oxide compound was performed at 400 ° C.
（実施例１６）
亜酸化銅化合物を製膜する際に６００℃で行った以外実施例１と同様に作製、測定した。
(Example 16)
Preparation and measurement were performed in the same manner as in Example 1 except that the formation of the cuprous oxide compound was performed at 600 ° C.
（比較例６）
亜酸化銅化合物を製膜する際に３５０℃で行った以外実施例１と同様に作製、測定した。
(Comparative Example 6)
Production and measurement were performed in the same manner as in Example 1 except that the formation of the cuprous oxide compound was performed at 350 ° C.
（比較例７）
亜酸化銅化合物を製膜する際に７５０℃で行った以外実施例１と同様に作製、測定した。
Production and measurement were performed in the same manner as in Example 1 except that the formation of the cuprous oxide compound was performed at 750 ° C.
表１〜３より、実施例１〜１６と比較例１〜７を比較すると、フォトルミネッセンススペクトルにおいて、650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値である第１の最高値（A）が600nm以上650nm以下での発光強度の最高値である第２の最高値（B）の100倍以下（A≦100B）であることで、優れた効率を達成することができることがわかる。さらに、フォトルミネッセンススペクトルにおいて100K以下の温度でフォトルミネッセンススペクトルを測定した場合において、650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値である第１の最高値（A）が600nm以上650nm以下での発光強度の最高値である第２の最高値（B）の３0倍以下（A≦30B）であることで、よりよい効率を達成することができることがわかる。 From Tables 1 to 3, when Examples 1 to 16 and Comparative Examples 1 to 7 are compared, in the photoluminescence spectrum, the first highest value (the highest value of the emission intensity in the wavelength range of more than 650 nm and not more than 1000 nm) ( When A) is 100 times or less (A ≦ 100B) of the second highest value (B), which is the highest value of the emission intensity at 600 nm or more and 650 nm or less, it can be seen that excellent efficiency can be achieved. Furthermore, when the photoluminescence spectrum is measured at a temperature of 100 K or less in the photoluminescence spectrum, the first maximum value (A), which is the highest value of the emission intensity in the wavelength range from 650 nm to 1000 nm, is 600 nm to 650 nm. It can be seen that better efficiency can be achieved by being 30 times or less (A ≦ 30B) the second highest value (B), which is the highest value of the emission intensity below.
同じ温度で作製した太陽電池の場合、透明電極を用いた実施例１〜６までの方が、金属電極を用いた実施例７〜１２よりも効率比が高かった。これは、第1電極上の少なくとも一部に酸化物が存在する方が、亜酸化銅形成時の酸素と電極の反応を適度に抑制することができるからである。 In the case of solar cells manufactured at the same temperature, the efficiency ratios of Examples 1 to 6 using the transparent electrode were higher than those of Examples 7 to 12 using the metal electrode. This is because the reaction between oxygen and the electrode during the formation of cuprous oxide can be appropriately suppressed when the oxide is present on at least a part of the first electrode.
また、光電変換層に対してＸＰＳ分析を行い、光電変換層をＸＰＳで分析した際に結合エネルギー値が930eV以上934eV以下の範囲に見られる亜酸化銅のピークにおいて、亜酸化銅のピークトップの値の２／３の値を通る水平直線と亜酸化銅のピークとが交わる第１の交点及び第２の交点があり、ピークトップからの水平直線へおろした垂線と水平直線とが交わる第３の交点があり、第１の交点及び第３の交点の成す第1の長さと第２の交点及び第３の交点の成す第2の長さの差の割合の平均が１５％以下であることも、太陽電池の変換効率を向上させることができる。これは、光電変換層の内部に存在する異相が少ないため光励起キャリアの再結合の中心となり変換効率を低下させることを防ぎ、光電変換層の質を向上させることや、意図しない波長域の光を吸収してしまうことを防ぐことができるからである。そのため、光電変換層（ｐ層、亜酸化銅）内部での短絡電流密度を向上させることができる。加えて、良好な界面が形成されることで、界面の欠陥準位が低減し、開放電圧を増大させることができる。更に、リーク成分が抑制されることや良質なコンタクトが形成されることにより形状因子も向上し、効率が向上させることができる。 In addition, the XPS analysis was performed on the photoelectric conversion layer, and when the photoelectric conversion layer was analyzed by XPS, the binding energy value was found to be in the range of 930 eV or more and 934 eV or less. There are a first intersection and a second intersection where a horizontal line passing through a value of 2/3 of the value intersects the peak of cuprous oxide, and a third line where a vertical line lowered from the peak top to the horizontal line intersects the horizontal line And the average of the ratio of the difference between the first length formed by the first and third intersections and the second length formed by the second and third intersections is 15% or less. Also, the conversion efficiency of the solar cell can be improved. This is because there is little heterogeneous phase present inside the photoelectric conversion layer, which prevents recombination of photoexcited carriers and prevents reduction in conversion efficiency, improves the quality of the photoelectric conversion layer, and prevents light in unintended wavelength ranges. This is because absorption can be prevented. Therefore, the short-circuit current density inside the photoelectric conversion layer (p layer, cuprous oxide) can be improved. In addition, by forming a favorable interface, defect levels at the interface can be reduced and the open-circuit voltage can be increased. Further, the suppression of the leak component and the formation of a good-quality contact improve the shape factor and improve the efficiency.
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。 Although the embodiment of the present invention has been described above, the present invention is not construed as being limited to the above-described embodiment, and can be embodied by modifying components in an implementation stage without departing from the scope of the invention. Further, various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, components of different embodiments may be appropriately combined as in a modification.
１００…太陽電池（第１太陽電池、トップセル）、１…基板、２…第１電極、３…光電変換層、４…ｎ型の化合物半導体層（ｎ型層）、５…第２電極、２００…多接合型太陽電池、２０１…第２太陽電池（ボトムセル）、３００…太陽電池モジュール、３０１…第１太陽電池モジュール、３０２…第２太陽電池モジュール、３０３…サブモジュール、４００…太陽光発電システム、４０１…太陽電池モジュール、４０２…コンバーター、４０３…蓄電池、４０４…負荷 100 solar cell (first solar cell, top cell), 1 substrate, 2 first electrode, 3 photoelectric conversion layer, 4 n-type compound semiconductor layer (n-type layer), 5 second electrode, 200: Multi-junction solar cell, 201: Second solar cell (bottom cell), 300: Solar cell module, 301: First solar cell module, 302: Second solar cell module, 303: Submodule, 400: Solar power generation System, 401: solar cell module, 402: converter, 403: storage battery, 404: load
Claims (8)
第２電極と、
前記第１電極と前記第２電極の間に設けられる光電変換層とを備え、
前記光電変換層を100K以下の温度でフォトルミネッセンススペクトルを測定した場合において、650ｎｍより大きく1000ｎｍ以下の範囲の波長域における発光強度の最高値である第１の最高値（A）が600nm以上650nm以下での発光強度の最高値である第２の最高値（B）の100倍以下（A≦100B）である太陽電池。 A first electrode;
A second electrode;
A photoelectric conversion layer provided between the first electrode and the second electrode,
When the photoluminescence spectrum of the photoelectric conversion layer is measured at a temperature of 100 K or less, the first highest value (A) of the emission intensity in a wavelength range of more than 650 nm and 1000 nm or less is 600 nm or more and 650 nm or less. A solar cell having 100 times or less (A ≦ 100B) of the second highest value (B), which is the highest value of the light emission intensity in the above.
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