Cu₃SbS₃ (CAS) thin films are synthesized by the conventional thermal evaporation technique. The induced effects in optical and morphological properties of these films upon the annealing process in temperature range 473–623 K are studied. X-ray diffraction (XRD) analyses reveal the amorphous nature of the as-deposited film which crystallizes in monoclinic crystal structure after annealing. The absorption coefficient, refractive index and film thickness are calculated by Swanipoel's method. The observed optical band gap (E_g) shows a decrease in its value from 1.88 to 1.61 eV after annealing which is consistent with the detected red shift of absorption edge in the transmission spectra. The fabrication and the current-voltage (J-V) characteristics of Al/n-Si/p-CAS/Ag junction at different annealing temperatures are investigated. Dark measurements reveal good rectification behavior ≈ 10². Under illumination, the best performance is achieved for annealed cell at 523 K with short circuit current (J_sc) = 6.65 mAcm², open circuit voltage (V_oc) = 0.3 V, fill factor (FF) = 30% and conversion efficiency (η) = 1.49%.