Device Characteristics of Band gap Tailored 10.04% Efficient CZTSSe Solar Cells Sprayed from Water-Based Solution

A diverse S/(S + Se) ratio of Cu2ZnSn(Sx,Se1–x)4 (CZTSSe) thin-film solar cells is derived by the water-based spray pyrolysis approach. By fine-tuning the S/(S + Se) ratio, base CZTSSe device efficiency has significantly improved from 7.02 to 10.04% by minimizing the Voc deficit up to 616 mV and increasing fill factor (FF) from 56.42 to 62.38%. As the S/(S + Se) ratio was increased from 0 to 0.4, surface compactness was observed to be improved with slightly decreased grain size, which increased shunt resistance and resultantly increased FF. However, when S-alloying was more than S/(S + Se) = 0.4, grain size decreased too much and had a detrimental effect on device performance. To deeply understand the role effect of the S/(S + Se) ratio, detailed spectroscopic analysis is performed with admittance spectroscopy, temperature-dependent current–voltage characteristic (J–V–T), time-resolved photoluminescence, and Raman depth profiling. Experimental results revealed that the different power conversion efficiency limiting factors were developed with various S/(S + Se) ratios. High density of deep defect states generated with the S/(S + Se) ≥ 40% content and larger conduction band offset observed with red kink were formed in the Se/(S + Se) ≥ 80% content. Hence, in order to get the high-efficient CZTSSe solar cell, fine tuning of the S/(S + Se) ratio is necessary.