Copper-Zinc-Tin-Sulphide (CZTS)/n-Si and Copper-Indium-Gallium-Selenide (CIGS)/n-Si hetero-junction solar cells have been manufactured using Pulse Laser Deposition (PLD) technique. Properties of both CZTS&CIGS ultrathin films have been produced in comparable thicknesses, analysed and compared to each other. CIGS ultrathin film has smaller main crystalline size but absorbs more light compared to CZTS. (Formula presented.) characteristics of CZTS/n-Si and CIGS/n-Si hetero-junctions have been obtained in the darkness and under light conditions. The ideality factor, barrier height, serial resistances of these hetero-junctions have been calculated by the traditional (Formula presented.) and Cheung-Cheung methods for the darkness. Although the serial resistance of CZTS hetero-junction has been found to be very low compared to CIGS hetero-junction, the efficiency and photocurrent of CZTS solar cell have been higher compared to those of CIGS solar cell (Formula presented.). The photoelectric outputs of CZTS/n-Si and CIGS/n-Si cells have been studied using SCAPS-1D programme. We have found/concluded difference in (Formula presented.) characteristics between CZTS/n-Si and CIGS/n-Si structures.