In Situ Forming of a 2D Inorganic Perovskite Capping Layer by Surface Reconstruction for Efficient and Stable CsPbI2Br Perovskite Solar Cells

Although inorganic perovskite solar cells (PSCs) have made remarkable progress, ambient instability and serious nonradiative recombination loss greatly impede their further development. Herein, we develop a novel surface reconstruction process to in situ grow a 2D inorganic perovskite capping layer on a 3D CsPbI₂Br perovskite surface via the dynamic methanol treatment and subsequent thermal annealing for simultaneously enhancing the stability and suppressing nonradiative recombination of inorganic CsPbI₂Br PSCs. The dynamic methanol treatment removes the surface defective regions of CsPbI₂Br perovskite and results in forming excessive PbI₂ on the CsPbI₂Br perovskite surface, and the subsequent thermal annealing triggers the surface reconstruction reaction of excessive PbI₂ with CsPbI₂Br that leads to in situ forming of a 2D CsPb₂I₄Br layer on the CsPbI₂Br perovskite surface, which effectively decreases the defect density and enhances the stability of CsPbI₂Br perovskite. As a result, the fabricated carbon-based CsPbI₂Br PSC displays a power conversion efficiency of 14.29%. Moreover, the CsPbI₂Br device with a 2D CsPb₂I₄Br layer displays superior stability, and the efficiency of the cell without encapsulation remains at over 90% of the original value after storing in ambient conditions for 900 h.