Cu 2 ZnSnS 4 (CZTS)-based solar cells show a promising performance in the field of sunlight-based energy production system. To increase the performance of CZTS-based solar cell, buffer layer optimization is still an obstacle. In this work, numerical simulations were performed on structures based on CZTS absorber layer, ZnO window layer, and transparent conducting layer n-ITO with different buffer layers using SCAPS-1D software to find a suitable buffer layer. Cadmium sulfide (CdS), zinc sulfide (ZnS) and their alloy cadmium zinc sulfide (Cd 0.4 Zn 0.6 S) were used as potential buffer layers to investigate the effect of buffer thickness, absorber thickness and temperature on open-circuit voltage (V oc), short-circuit current (J sc), fill factor (FF) and efficiency (η) of the solar cell. The optimum efficiencies using these three buffer layers are around 11.20%. Among these three buffers, Cd 0.4 Zn 0.6 S is more preferable as CdS suffers from toxicity problem and ZnS shows drastic change in performance parameters. The simulation results can give important guideline for the fabrication of high-efficiency CZTS solar cell.