In Situ Forming a 0D Inorganic Perovskite Capping Layer via a Surface Reconstruction Process for High-Performance Inorganic Perovskite Solar Cells

Inorganic CsPbX₃ perovskite solar cells have made great progress over the past several years. Nevertheless, the vulnerable surface of the CsPbX₃ perovskite deteriorates the device stability and impedes the further development of the device performance. Herein, a surface reconstruction method is proposed to in situ construct a 0D Cs₄PbI_1.5Br_4.5 capping layer on top of a 3D CsPbI_1.5Br_1.5 perovskite for simultaneously decreasing the surface defects and promoting the stability of the CsPbI_1.5Br_1.5 perovskite. It is found that constructing a 0D Cs₄PbI_1.5Br_4.5 capping layer atop a 3D CsPbI_1.5Br_1.5 perovskite not only remarkably enhances the stability of the CsPbI_1.5Br_1.5 perovskite but also creates the favorable energy level for the interface charge separation. In addition, this surface reconstruction process causes the secondary crystallization of the CsPbI_1.5Br_1.5 perovskite, decreasing the perovskite defects and improving the perovskite quality. These favorable features result in a remarkable reduction of nonradiative recombination. As a result, the carbon-based CsPbI_1.5Br_1.5 device exhibits a promoted performance with a power conversion efficiency of up to 12.93%. In addition, the cell without any encapsulation maintains ∼94% the original efficiency after 1080 h aging under an ambient environment.