Evaluation of sputtering damage in Cu2ZnSn(S,Se)4 solar cells with CdS and (Cd,Zn)S buffer layers by photoluminescence measurement

Cu2ZnSn(S,Se)(4) (CZTSSe) solar cells are fabricated with CdS and (Cd,Zn)S buffer layers of different thicknesses to investigate sputtering damage on the absorber surfaces during ZnO:Al/ZnO layer deposition. In this work, the sputtering damage is scrutinized by photoluminescence (PL) measurement. The damage (i.e., non-radiative recombination centers) near the absorber surfaces investigated on the basis of PL peak intensity decreases with increasing thickness of the buffer layer. Furthermore, the intensity in the solar cells with the CdS buffer is higher than that with the (Cd,Zn)S buffer layer, suggesting that the CdS buffer layer demonstrates better capability of preventing sputtering damage near the CZTSSe surface than the (Cd,Zn)S buffer. PL ratio defined as the ratio of the PL peak intensity after sputtering to the PL peak intensity before sputtering is utilized to quantify sputtering damage. The solar cell performance increases with increasing PL ratio up to 0.5, followed by saturation at a ratio higher than 0.5. Taken together, PL ratio is proposed as a tool for monitoring sputtering damage for improving cell performance. (c) 2015 The Japan Society of Applied Physics