成果報告書詳細
管理番号20140000000824
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)ポストシリコン超高効率太陽電池の研究開発
公開日2015/4/15
報告書年度2013 - 2013
委託先名東京大学先端科学技術研究センター
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R & D on Innovative Solar Cells (International Research Center for Innovative Solar Cell Program) “Research and Development of Post-silicon solar cells for ultra-high efficiencies” (FY2008-FY2014) FY2013 Annual Report

 In order to implement a step potential superlattice in a triple junction cell, MOCVD growth was done on 6-degree-off substrate. The use of TEG instead of TMG drastically reduced the issue of carbon impurity and improved the crystal quality grown at as low as 510C. This led to a GaAs cell with Isc of 14.7 mA/cm2 and FF of 77% under a top-cell InGaP filter. An increased stacking number up to 100 should result in a target of 17 mA/cm2.
 The GaInNAsSb subcell structures were fabricated on Ge bottom cell by MBE. The Voc measured for a GaInNAsSb/Ge 2-junction cell was 0.64V, and that for a first-trial InGaP/GaAs/GaInNAs/Ge 4-junction tandem cell which was fabricated by wafer-shuttle was 2.20V. By increasing the GaInNAsSb layer thickness from 1 to 2um, EQE in the long wavelength region improved by 70~90%.
 InGaN cells were developed aiming at the mechanically-stacked top cells by the use of pulsed sputtering deposition (PSD). The InGaN/GaN multiple quantum wells (MQWS) with high In content up to 46% and p-type GaN films with high hole concentrations were successfully grown on nitrogen polar planes. The improvement of InGaN crystalline quality was achieved by the use of bulk GaN substrate, which leads to a drastic increase in fill factor. These new techniques enable us to increase the efficiency of InGaN cells.
 Bottom cells for MJ solar cells, consisting of ZnO nanowire arrays and PbS QDs, were fabricated and the highest external quantum efficiency of 60% at 1050 nm was obtained. Regarding photocurrent enhancement by metal nanoparticles, the wavelength region for the enhancement was red-shifted by increasing anisotropy of the nanoparticles.
 Thin-film InAs/GaAs QD intermediate band solar cell (IBSC) was fabricated by epitaxial lift-off which resulted in an improved EQE up to 7% in the long wavelength region. The Isc was >20 mA/cm2. Further, two-step absorption rate was improved by using higher band offset AlGaAs barriers. A plane-wave expanded 8-band k.p calculation was used to show that the absorption coefficient between the bound states in IB and higher states in band continuum is ~500cm-1.
 The light trapping structure was improved for the enhancement of absorption by nanostructures in the sub-bandgap region of GaAs. A heat-tolerant polymer was used to glue the thin-film cell onto a support substrate. It resulted in an enhanced fill factor of 77%. The backside light scattering structure now employs a thin SiO2 layer between GaAs grating and gold reflection layer. As a result, 20% efficiency was obtained for the thin-film GaAs cell with QWs. The light trapping strategy is now extended to QD cells. Further, monolithic integration of series-connected cells was attempted for InGaP/GaAs 2-junction cells to reduce the effect of Rs under concentration.
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