In this study, Ag/CZTS/Si/Al heterojunction solar cells were produced depending on some parameters of CZTS ultrathin active film layers grown on a n-Si wafer by PLD technique. CZTS ultrathin films have been produced as a function of the number of laser pulses and then annealed in a tube oven as a function of sulfurization temperature. The crystal structure, the optical and morphological properties of grown&annealed CZTS ultrathin films were examined by XRD, UV-vis spectra, AFM, respectively. The electrical characteristics of CZTS heterojunction solar cell in the darkness, which were investigated by the conventional J-V Method, Cheung Cheung Method and Norde Method. As the thickness of CZTS ultrathin films increased, the forward current of CZTS heterojunctions increased and their ideality factor, serial resistance and barrier height decreased. Also, the efficiency of Ag/CZTS/Si/Al heterojunction solar cells have been examined and characterised as a function of CZTS ultrathin film thickness under the illumination conditions. J-V curves of CZTS heterojunction solar cells were determined under AM 1.5 solar radiation in 80 MW/cm2, all CZTS heterojunction solar cells have exhibited the photovoltaic behaviour. Jsc, Voc, FF, η parameters of Ag/CZTS/Si/Al heterojunction solar cells were measured, interpreted and compared with each other.