In this work, ZnO thin films have been produced on p-Si wafer depending on number of laser pulses applied using pulse laser deposition (PLD) technique at room temperature conditions. Three different thicknesses of ZnO thin films (ZnO1, ZnO2 and ZnO3) have been produced by applying 18,000, 36,000 and 54,000 laser pulses and thicknesses of these produced three thin films have been measured to be 41 nm, 70 nm, 197 nm, respectively. It is observed in this work that while thicknesses of ZnO thin films increases, crystal structure of thin films develops, their grain size increase while their band gaps decrease. Ag/ZnO/Si/Au heterojunction diodes have been produced based on ZnO1, ZnO2 and ZnO3 thin films. After that, effect of thickness of thin film on electrical properties of diodes produced depending on number of laser pulses has been analyzed in detail. I–V characteristics of ZnO/Si heterojunction diodes produced have also been measured in darkness environment and under illumination conditions (AM 1.5 solar radiation of 80 mW/cm2) and results obtained have been interpreted and a conclusion has been made in this work. Furthermore, ideality factors, barrier heights and serial resistivities of these diodes have been calculated using conventional thermionic emission theory, Norde and Cheung-Cheung methods and then results obtained from analytical methods have been interpreted in detail in the present article. ZnO heterojunction diodes have exhibited photovoltaic properties under illumination conditions. It has been observed that as thickness of ZnO thin film is increased, Jsc and η values of the hetero junction diodes are increased. ZnO-3A hetero junction diode has exhibited the most improved photovoltaic performance. We have also theoretically investigated photo-electric properties of ZnO-3A heterojunction diode using SCAPS-1D packed software. The resulted J–V characteristics have been found very similar to measured counterparts.