Overcoming the Voc limitation of CZTSe solar cells

Abstract : The Voc deficit issue is considered to be the most significant limitation of high-performance kesterite devices [1]. Secondary phases, defects, band tailing and interface recombination at the kesterite/CdS heterojunction are possible reasons for the low Voc. Raman spectroscopy and PL imaging are applied here for the detection of these phenomena. Their impact on Voc and the efficiency of CZTSe devices is investigated. Process steps are optimized so as to limit their negative influence. Control of secondary phase removal and optimization of the CZTSe/CdS interface lead to significant Voc enhancement. CZTSe devices with 466 mV open circuit voltage and 8.2% power conversion efficiency are achieved. An even higher Voc of 490 mV is obtained for a 4.5% CZTSe/In2S3 device.