Antimony sulfide (Sb2S3) is a promising material for photovoltaic applications because of its high absorption coefficient, environmental friendliness and low cost. Nevertheless, the conversion efficiency of Sb2S3 solar cells severely deviates from theoretical predictions, and the interface between CdS and Sb2S3 is crucial for the overall performance. In this study, we conducted a highly effective sodium borohydride (NaBH4) etching to modify the CdS/Sb2S3 interface, aiming to improve the device performance. The NaBH4 etching led to a reduction in surface roughness and an enhancement in the hydrophilicity of the CdS layer, creating a more conducive environment for the subsequent deposition of the Sb2S3 absorber layer. Simultaneously, the reduction of cadmium oxide serves to optimize interfacial energy alignment and minimize recombination losses. Ultimately, our full-inorganic Sb2S3 solar cells, featuring the configuration FTO/CdS/Sb2S3/MnS/Carbon, attain a PCE of 6.26%. This marks a significant improvement of 15% compared to cells without NaBH4 etching. This study presents a feasible and efficient perspective for modifying the CdS/Sb2S3 interface, thereby enhancing the performance of Sb-based solar cells.