One of the research hotspots in thin film solar cell technology is to seek the suitable absorber layer materials to replace cadmium telluride and copper indium gallium selenium. Recently, germanium selenide (GeSe) with excellent photoelectric property has entered the field of vision of photovoltaic researchers. The main factors affecting the performance of heterojunction solar cell are the material properties of each functional layer, the device configuration, and the interface characteristics at the heterostructure. In this study, we utilize GeSe as the absorber layer, and assemble it with stable TiO₂ as electron transport layer and with Cu₂O as hole transport layer, respectively, into a heterojunction solar cell with the FTO/TiO₂/GeSe/Cu₂O/Metal structure. The TiO₂ and Cu₂O can form small spike-like conduction band offset and valence band offset with the absorber layer, respectively, which do not hinder majority carrier transport but can effectively suppress carrier recombination at the heterointerface. Subsequently, the wxAMPS software is used to simulate and analyze the effects of functional layer material parameters, heterointerface characteristics, and operating temperature on the performance parameters of the proposed solar cell. Considering the practical application, the relevant material parameters are selected carefully. After being optimized at 300 K, the proposed GeSe heterojunction solar cell can reach an open circuit voltage of 0.752 V, a short circuit current of 40.71 mA·cm^–2, a filling factor of 82.89%, and a conversion efficiency of 25.39%. It is anticipated from the results that the GeSe based heterojunction solar cell with a structure of FTO/TiO₂/GeSe/Cu₂O/Au has the potential to become a high-efficiency, low toxicity, and low-cost photovoltaic device. Simulation analysis also provides some references for designing and preparing the heterojunction solar cells.