成果報告書詳細
管理番号20130000000288
タイトル*平成24年度中間年報 新エネルギー技術研究開発 革新的太陽光発電技術研究開発(革新型太陽電池国際研究拠点整備事業)低倍率集光型薄膜フルスペクトル太陽電池の研究開発(構造設計とカルコパイライト系トップセル)
公開日2013/6/22
報告書年度2012 - 2012
委託先名立命館大学
プロジェクト番号P07015
部署名新エネルギー部
和文要約
英文要約Title:Thin Film Full Spectrum Solar Cells with Low Concentration Ratios (Design of Thin-Film Full Spectrum Solar Cells and Development of Cu(In,Al)S2 Top Cells) (FY2008-FY2014) FY2012 Annual Report

Cu(In,Al)S2 (CIAS) solar cells for a top cell and lift-off technology to realize full spectrum solar cells are developed. In this fiscal year, CIAS thin film growth and cell fabrication were performed but the solar cell efficiency could not be improved. Thus, at the same time we worked on lift-off technology of chalcopyrite solar cells. High efficiency chalcopyrite solar cells typically employ substrate-type structure due to process temperature limitation. Buffer and window layers are generally deposited after chalcopyrite thin film growth. If chalcopyrite thin films are deposited on buffer and window layers at 550 degree Celsius which is typical temperature for high quality chalcopyrite growth, buffer and window layers deteriorate and thus output voltage of the device drastically decreases. Thus, in the current understanding, substrate-type structure is important to realize high efficiency chalcopyrite solar cells. In the lift-off technology, an alternative glass substrate is attached on the surface of high efficiency chalcopyrite solar cells and peeled off from chalcopyrite and back contact interface. Then, transparent electrode is deposited on the peeled-off surface of the chalcopyrite film to fabricate high efficiency superstrate-type chalcopyrite solar cells with transparency for sub-Eg light. Our final goal is to establish the lift-off technology for high efficiency Cu(In,Ga)Se2 (CIGS) and Ag(In,Ga)Se2 (AIGS) solar cells and to fabricate high efficiency full-spectrum solar cells. In this fiscal year, the basic process of the lift-off technology for CIGS solar cells was developed. First, substrate-type CIGS solar cells with Al-NiCr/ZnO:Al/ZnO/CdS/CIGS/Mo/Glass structure was fabricated. Then, alternative glass was attached on the cell surface with transparent glue. The glass/glue/Al-NiCr/ZnO:Al/ZnO/CdS/CIGS structure was peeled off at CIGS/Mo interface. Then, the back contact of ZnO:Al was directly deposited on the peeled off surface. In this cell, a back junction was formed at CIGS/ZnO:Al interface and photocurrent can not be obtained due to n-p-n structure to induce photo-generated hole confinement. To solve this problem, a back contact buffer layer of MoOx (~30 nm in thickness) was inserted between CIGS and back contact. In this case, photocurrent collection was improved and short-circuit current of almost 70% for the reference cell was obtained. However, fill factor was low compared to the reference cell due to double-diode like current-voltage behavior. Thus, the thickness and material of the back contact buffer should be optimized to realize high efficiency lift-off solar cells.
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