By using vacuum evaporation, thin films of the (CdS)0.75-(PbS)0.25 alloy have been deposited to form a nanocrystalline composite. Investigations were made into the morphology, electrical, optical and I-V characteristics of (CdS)0.75-(PbS)0.25 films asdeposited and after annealing at various temperatures. According to AFM measurements, the values of grain sizes rise as annealing temperatures rise, showing that the films' crystallinity has been increased through heat treatment. In addition, heat treatment results in an increase in surface roughness values, suggesting rougher films that could be employed in more applications. The prepared films have direct energy band gaps, and these band gaps increase with the increase in the degrees of annealing temperature. Additionally, Urbach energy values decrease with an increase in annealing temperature degrees, indicating a reduction in the tail defects and an enhancement in crystal structure through annealing. The produced films' conductivity raise when temperature in the range (RT-473)K increased, demonstrating that they are semiconducting films. At comparatively lower temperature degrees, the conduction is caused by carriers that are stimulated into localized states at the band edges. At relatively higher temperatures, the conductivity appears to be substantially temperature-dependent. As a result, the conduction mechanism results from carriers being excited into extended states beyond mobility edges. The photovoltaic measurement (I–V) properties, open circuit voltage, short circuit current, efficiency and fill factor of (CdS)0.75-(PbS)0.25 heterostructure cells have been examined under 100mW/cm2 . Interestingly, rising annealing had enhanced photovoltaic cell performances; the solar cell had shown its highest efficiency (0.42%) at 573K. From XRD the structures are polycrystalline with cubic and hexagonal structures indicating that there’s a mix of phases of PbS and CdS, the grain size and intensity raise with annealing temperatures.