Thin film solar cell along with enhanced absorption property will be the best, so combination of SiGe alloy is considered. The paper presented here consists of a numerical model of Si/Si1−xGex heterojunction solar cell. The addition of Ge content to Si layer will affect the property of material. The research has investigated characteristics such as short circuit current density (Jsc), generation rate G , absorption coefficient (α), and open circuit voltage (Voc), power, fill factor (FF) with optimal Ge concentration. The speculative determination of appropriate germanium mole fraction is done to get the maximized thin-film solar cell efficiency.