成果報告書詳細
管理番号20120000000149
タイトル*平成23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2012/6/20
報告書年度2011 - 2011
委託先名パナソニック
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) (FY2008-2012) FY2011 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 25%. 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, short circuit current (Jsc) of 13.4 mA/cm2 and fill factor (FF) of 0.48. However, Jsc increased but Voc decreased with increasing the preparation temperature of the ZCIS films. It is one of critical issues on a simultaneous improvement of an efficiency and Voc. The reason of a decrease of Voc with increasing the preparation temperature may be attributed to the interdiffusion between the In2S3 and ZCIS films. We have analyzed on the interdiffusion in detail and examined an improvement of the efficiency and Voc. EDX analysis on cross sectional TEM images of the In2S3 / ZCIS films showed that a large amount of Cu and a small amount of Zn diffused from the ZCIS to the In2S3 films at the high preparation temperature of the ZCIS films. The diffusion of Cu to the In2S3 films formed the Zn poor ZCIS layers. The lower Voc than the expected value from the bandgap of the ZCIS films is attributed to the low bandgap layers formed in the depletion layers by the diffusion of Cu. Furthermore, the interdiffusion could increase the interface recombination centers, resulting in the drop of the Voc. In order to suppress the formation of the low bandgap layers, thin ZICS layers with the higher Zn/Metal ratios than the bulk ZCIS films were inserted between the In2S3 and ZCIS films. The wide bandgap insertion layers with the higher Zn/Metal ratios than the bulk films can improve on the Voc. FF and efficiency increased but Jsc decreased with increasing the Zn/Metal ratio of the insertion layers. The Voc reached a maximum at 0.4 of the Zn/Metal ratio. The high Voc and efficiency will be simultaneously achieved by optimization of the insertion layer. In addition, the quantum efficiency of the solar cells and transmittance at the longer wavelengths than the absorption edge of the ZCIS film were improved by increasing preparation temperature of the ZCIS films with the insertion layers controlling the interdiffusion. The quantum efficiency and transmittance reached 90% of the target values. The target efficiency will be achieved by developing the elemental technologies established by this fiscal year.
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