Rear point contact structures for performance enhancement of semi-transparent ultrathin Cu(In,Ga)Se2 solar cells

Semi-transparent ultrathin Cu(In,Ga)Se-2 (CIGSe) solar cells offer many promising applications but their efficiencies are still limited. In this work, SiO2 point contact structures were prepared using nanosphere lithography on Sn:In2O3 (ITO) substrate and ultrathin CIGSe solar cells were fabricated on top. It was discovered that the SiO2 point contact structure at the CIGSe/ITO interface behaves significantly different from at the CIGSe/Mo interface and does not improve the rear interface reflectivity or short-circuit current density. However, the SiO2 point contact structure brings pronounced electrical benefits, arising from the joint effect of reduced back recombination and induced field effect by internal charges. Semi-transparent ultrathin CIGSe solar cells with an absorber thickness of 380 nm exhibited a significant increase in open circuit voltage of 26 mV and fill factor of 9.4% (absolute). Consequently, the efficiency is improved by 23% (from absolute 6.8%-8.4%).