<italic>In situ</italic> construction of 0D Cs₄PbI₅Br/3D CsPbI₂Br bilayer heterostructure for enhancing the photovoltaic performance of CsPbI₂Br inorganic perovskite solar cells

Passivating the surface defects and enhancing the stability of inorganic perovskites through surface engineering are effective strategies for improving the photovoltaic performance of inorganic perovskite solar cells. Here, a 0D Cs4PbI5Br/3D CsPbI2Br bilayer heterostructure is in situ constructed through forming a 0D Cs4PbI5Br capping layer atop 3D CsPbI2Br perovskite by the surface reaction triggered by CsI solution treatment and subsequent annealing process at 220°C. The formation of 0D Cs4PbI5Br/3D CsPbI2Br bilayer heterostructure considerably reduces the defects of CsPbI2Br perovskite and enhances the stability of CsPbI2Br perovskite. Meanwhile, the built-in electric field of 0D Cs4PbI5Br/3D CsPbI2Br bilayer heterostructure promotes the hole extraction and interface transport and effectively suppresses the interface charge recombination. Consequently, the assembled carbon-based 0D/3D heterostructure CsPbI2Br perovskite solar cell without a hole-transport layer demonstrates a power conversion efficiency of 15.24%. Furthermore, 0D/3D heterostructure CsPbI2Br perovskite solar cell without any encapsulation remains ~94% of the initial efficiency after 1080 h storage in ambient environment, suggesting an excellent stability.