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 Cs4PbI1.5Br4.5 capping layer on top of a 3D CsPbI1.5Br1.5 perovskite for simultaneously decreasing the surface defects and promoting the stability of the CsPbI1.5Br1.5 perovskite. It is found that constructing a 0D Cs4PbI1.5Br4.5 capping layer atop a 3D CsPbI1.5Br1.5 perovskite not only remarkably enhances the stability of the CsPbI1.5Br1.5 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 CsPbI1.5Br1.5 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 CsPbI1.5Br1.5 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.