Antimony selenide (Sb2Se3) thin film solar cells were prepared by vapor transport deposition, and cesium chloride (CsCl2) solution was used to treat the upper interface of the device. Meanwhile, a series of characterizations of the thin film and the device were also performed. The study shows that the back contact treatment of CsCl2 solution can not only improve the carrier collection and reduce upper interface recombination of the device, but also optimize the crystallinity, surface roughness and optoelectronic performance of thin film. Based on the device structure of FTO/CdS/Sb2Se3/CsCl2/Au, a high-efficiency Sb2Se3 thin film solar cell with efficiency of 6.32% are obtained, which is 12% higher than that of the basic device. The research may provide some guidance to further development of Sb2Se3 thin film solar cells and other similar types of semiconductor photovoltaic devices.