成果報告書詳細
管理番号20140000000713
タイトル*平成25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) 高度秩序構造を有する薄膜多接合太陽電池の研究開発(構造制御化合物ワイドギャップ)
公開日2015/4/24
報告書年度2013 - 2013
委託先名パナソニック株式会社
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: Research and Development on Innovative Solar Cells (International Research Center for Innovative Solar Cell Program) Exploring Novel Thin Multi-junction Solar Cells with Highly-ordered Structure (Wide-gap Compound Solar Cells with Designed Structure) (FY2008-2014) FY2013 Annual Report

Our objectives are to establish technologies for high efficiency wide-gap compound solar cells as a top cell of multi-junction solar cells achieving an efficiency of 30%. We have focused on a wide bandgap material of ZnCuInS2 (ZCIS) as a novel absorber. The ZCIS solar cells with a superstrate configuration of glass/ITO/ TiO2/In2S3/ZCIS/Au showed an efficiency of 4.4% with an open circuit voltage (Voc) of 0.68V, a short circuit current (Jsc) of 13.4 mA/cm2 and a fill factor (FF) of 0.48. However, it is difficult to improve the efficiency of the ZCIS solar cells because the ZCIS films have an impurity phase of In2S3 and poor grain growth induced by low growth temperatures of the spray pyrolysis deposition. We have developed CuGaSe2 based chalcopyrite films as a novel wide-gap material in order to improve an efficiency of the top cells. The chalcopyrite CuGaSe2 has wide composition ratios of Cu/Ga between 0.7 and 1.0. We have focused on Zn incorporated CuGaSe2 (ZnCuGaSe2, ZCGS) in order to control the bandgap of 1.8eV for the top cells. ZCGS films were prepared by thermal annealing of precursors including Zn, Cu and Ga in order to enhance the grain growth under high temperatures. X-ray diffraction patterns showed that the ZCGS films had the chalcopyrite structure since the characteristic peak of 211 and the split of 220 and 204 peaks were observed. Impurity phases such as Ga2Se3 and GaSe were not observed by the incorporation of Zn. The bandgap of the ZCGS film showed the bowing curve with increasing the Zn/Metal (Metal =Zn+Cu+Ga) ratio. The bandgap decreased up to Zn/Metal ratio of 0.1 and increased with increasing the Zn/Metal ratio over 0.1. The bandgap reached to 1.75 eV at the Zn/Metal ratio of 0.37. ZCGS solar cells with a substrate configuration of ZnO:Al/ZnO/CdS/ZCGS/Mo/glass were fabricated. A short circuit current (Jsc) of the ZCGS solar cell increased up to the Zn/Metal ratio of 0.2, and decreased with increasing the Zn/Metal ratio moreover. The variation of the Jsc is almost in agreement with the bandgap variation for the Zn/Metal ratio. An open circuit voltage increased with increasing the Zn/Metal ratio and reached to 0.91V at the Zn/Metal ratio of 0.37. A fill factor (FF) increased up to the Zn/Metal ratio of 0.3. As a result, a conversion efficiency of 8.5 % have been achieved at the bandgap of 1.70eV corresponding to the Zn/Metal content of 0.3. The quantum efficiency of the cell with the highest efficiency showed over 90% at the visible wavelengths, which is one of the technical targets at 2014. We have observed the Zn rich and poor layers in the ZCGS film. The bandgap can widen to 1.8 eV by optimizing the annealing for uniform distribution of Zn. Furthermore, multi-junction solar cells will be fabricated using smart stacking of our top cells and bottom cells in order to show the possibility of efficiency over 30%.
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