Due to non-toxicity and earth abundancy of raw materials, CZTS grabbing the attention of researchers to make it highly efficient and cost-effective solar cell harvesting. Thin-film CZTS based solar cell of higher efficiency reported with conventional CdS layer. Toxicity of Cd influences to reduce the thickness of the CdS buffer layer without compromising with the efficiency. The present paper deals with CdS/In2S3 and CdS/ZnS hybrid buffer layer which is more efficient than the solar cell using only the CdS buffer layer. The reduced thickness of the CdS layer in CZTS/CdS/In2S3/ZnO: Al and CZTS/CdS/ZnS/ZnO: Al structures have been optimized by using SCAPS-1D simulation software. This study reveals that there is an enhancement in the performance of solar cells from eta = 15.68% with CdS to eta = 16.52% with CdS/In2S3 and eta = 15.81% with CdS/ZnS hybrid buffer layer. Variation in PV parameters with a variation of the thickness of the buffer and absorber layer has been optimized. The acceptor density of CZTS/CdS/In2S3 and CZTS/CdS/ZnS was varied and results have been optimized. A numerical study of both structures on the photovoltaic performance of CZTS solar cells has been done by using SCAPS-1D simulation software.