Abstract: Germanous selenide (GeSe) has attracted extensive attention in recent years because of its abundant raw material reserves, green, non-toxic, simple preparation process and stable properties. GeSe thin films were prepared by close-space sublimation method. The crystallization behavior of GeSe thin films was analyzed and optimized for solar cells with FTO/CdS/GeSe/poly(3-hexylthiophene) (P3 HT)/C device structure. Firstly, the annealing process is introduced after the evaporation step, which can effectively promote the crystallization of GeSe thin film, so that the photoelectric conversion efficiency (PCE) of GeSe solar cells can be increased to 0.743%. Subsequently, by adjusting the crystallization characteristics of the GeSe film by the substrate temperature, it is found that the increase of the substrate temperature is conducive to the crystallization of the GeSe film, but when the substrate temperature is more than 300℃, the excessive temperature will make the GeSe desurbed from the substrate, resulting in a decrease in the degree of crystallization and rapid degradation of the device performance. At the optimum substrate temperature of 280℃, GeSe films have the largest grain size and the strongest light absorption, the highest electron lifetime (τ) and the highest electrical conductivity (σ), and the PCE of 2.130%, where the open circuit voltage (V_OC) is 0.299V, and the short circuit current density (J_SC) is 16.815 mA·cm⁻². The filling factor (FF) is 42.137%. The above research provides a feasible technical route for the preparation and optimization of high crystalline GeSe solar cells.