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In this work, the influence of molar concentration of CuCl2 on copper sulfide Cu2S film synthesized by chemical bath deposition and on the performance of p-Cu2S/p-Si heterojunction photodetector was studied. The effect of copper chloride concentration on the structural, optical properties and electrical properties of Cu2S film was investigated. The optical studies show that the optical energy gap varied from 2.68 to 2.8 eV as the concentration varied from 0.06 to 0.15 M. X-ray diffraction XRD results confirm that the deposition films having of monoclinic chalcocite phase. Scanning electron microscope SEM investigation illustrate the formation of nanostructured Cu2S film with particle size ranged from 50 to80 nm depending on the copper chloride concentration. Two Raman peaks were observed located at 265 and 470 cm−1 assigned to the Cu–S bond vibration and vibrational stretching mode, respectively. The mobility of charge carriers in the film and the electrical conductivity of the film were investigated as a function of copper chloride concentration. Dark and illuminated I-V characteristics of p-Cu2S/p-Si heterojunction HJ photodetectors were measured at room temperature. The best rectification was for heterojunction prepared at 0.13 M CuCl2. The maximum responsivity of the photodetector was about 0.67A/W at 450 nm for photodetector prepared at 0.13 M. [ABSTRACT FROM AUTHOR]