perovskites have been widely applied in photoelectric devices due to their excellent optical and electrical properties. However, the low optical absorption of their ultrathin thickness inhibits photoelectron generation and thus limits their performances. Herein, we constructed 2D CsPbBr 3 devices of composite structures by combining them with g-C 3 N 4 (CN) and graphene oxide (GO). As compared to CsPbBr 3 devices, the photocurrents of GO/CsPbBr 3 and CN/CsPbBr 3 devices increase by 68 and 114%, respectively. Based on experimental spectra in combination with the finiteelement method (FEM), the reflectivity values of GO/CsPbBr 3 and CN/CsPbBr 3 devices are, respectively, reduced by 21 and 33%, and therefore absorption coefficients are increased by 18 and 28%, respectively, and the corresponding internal quantum efficiencies are increased by 63 and 96%, respectively, in comparison to the CsPbBr 3 devices. Furthermore, we have quantitatively determined the linear relationship between the absorption coefficient and the photocurrent based on the diffusion theory of semiconductors. A general approach for improving the optoelectronic performance can be extended to other devices by constructing composite structures with strong photon absorption and low reflection.