成果報告書詳細
管理番号20130000000223
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)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2013/10/25
報告書年度2012 - 2012
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) FY2012 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, a short circuit current (Jsc) of 13.4 mA/cm2 and a 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. In order to suppress the interdiffusion, we have fabricated substrate type solar cells with the In2S3 films prepared on the ZCIS films at reverse of the superstrate cells. We have analyzed the interdiffusion by the EDX analysis on cross sectional TEM images of the In2S3 / ZCIS films. The thickness of the interdiffusion layer between the In2S3 and ZCIS films of the substrate cell was about 15nm. It is about one-fifth thickness of the interdiffusion layer of the superstrate cell. This result shows that the interdiffusion of the elements such as Cu, In and Zn was suppressed in the substrate cell because the In2S3 films are prepared at low temperature on the ZCIS films prepared formerly at high temperature. The substrate cell showed an efficiency of 1.25% with Voc of 0.629V, Jsc of 3.42 mA/cm2 and FF of 0.580. The FF highest by the former has been achieved in the ZCIS solar cells. This is due to improvement of the diode quality by suppression of the interdiffusion at the interface of pn junction. However, Jsc was a low value of about one-third of the superstrate cell. The electron beam induced current (EBIC) measurement was carried out to estimate the carrier generation depth. The EBIC signals were observed only in the depth of 0.2 micrometer from the interface in the ZCIS film. The carriers excited in the residual thickness of 0.8 micrometer of the ZCIS films recombine. The Jsc of the substrate cell decreased due to the insufficient collection of the carriers. The long carrier lifetime by the high quality of the ZCIS film and long carrier diffusion length by graded bandgap profiles of the ZCIS film will be required in order to increase Jsc. In addition, the transmittance at the wavelength longer than the absorption edge of the ZCIS film was measured as an important factor to achieve a high efficiency of the multi-junction solar cells. The substrate cell has achieved the transmittance of 80% which is target at 2012 by a decrease of the absorption of the impurity from the interdiffusion in the ZCIS film. The target efficiency at 2014 will be achieved by developing the elemental technologies established by this fiscal year.
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