成果報告書詳細
管理番号20130000000680
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
公開日2014/8/27
報告書年度2012 - 2012
委託先名国立大学法人東京工業大学
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 (FY2008-FY2014) FY2012 Annual Report

In order to realize thin-film solar cells with conversion efficiencies over 40%, we are developing novel absorber materials. (1) Si Based Thin Film Concentrators: To increase the performance of thin-film solar cells, solar spectrum splitting technique has been considered and studied. It was found from the simulation that the total efficiency of nearly 25% can be obtained at the splitting wavelength of 600 nm for thin-film type solar cell using a-Si and CIGS as the top and bottom cells, respectively. The experiment has been carried out to verify the simulation results. By cell and splitter optimization, up to now a total efficiency of 22 % has been obtained at the splitting wavelength of 614 nm which is similar to the simulation results. Cu doping of CdTe layer in CdTe solar cells without using Cu-doped carbon electrode was investigated for developing transparent back contacts. Cell performance was drastically improved by heat treatment after coating of Cu-doped diethylene glycol monobutyl ether. (2) Band Gap Control of Nano Dots: The insertion of the TiO2:Nb layer improved the performance of Si-QDSL solar cells. A Voc of 529 mV and a Jsc of 1.60 mA/cm2 were achieved using the TiO2:Nb layer. This improvement is due to the suppression of impurity diffusion and increasing the thickness of a depletion region. We also measured the world’s first I-V characteristics under concentrated light. As a result, Voc increased to 649 mV at 19.7 suns. (3) Chalcopyrite Based Thin Film Concentrators: In order to improve the film quality and enhance the efficiency, we have pointed out that the high-temperature growth has great significance for chalcopyrite materials. For Cu(In,Ga)Se2, it was found that the suppression of In re-evaporation was quite important at high temperatures, and the efficiency of 12.4% was obtained with a bandgap of 1.35eV by controlling the Se vapor pressure. In case of Au(In,Ga)Se2 (AIGS) solar cell, the low FF is one of major problems, and the low quality of AIGS/Mo contact properties is possible candidate. (4) Bandgap Engineering of Strained Ge: For the sake of realization of strained-Ge solar cells, we have started the research on the heterojunction Ge solar cells. Since Ge has high refractive index and it should absorb photons with longer wavelength, the reduction of reflectance in the long wavelength region is significant. Therefore we proposed several transparent contacts with an antireflection function. Additionally, the passivation effect of a-SiO layer on the carrier lifetime was confirmed by the --PCD method. (5) Surface Plasmon: The metal nanoparticle films fabricated by the various methods on a-Si layer had not only wavelength-selective reflection properties, but also wavelength-selective absorption effect.
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