Assembling the 2D-3D-2D Heterostructure of Quasi-2D Perovskites for High-Performance Solar Cells.

Quasi-two-dimensional (quasi-2D) layered perovskites with mixed dimensions offer a promising avenue for stable and efficient solar cells. However, randomly distributed three-dimensional (3D) perovskites near the film surface limit the device performance of quasi-2D perovskites due to increased nonradiative recombination and ion migration. Herein, we construct a 2D ( = 4 top)-3D-2D ( = 2 bottom) heterostructure of quasi-2D perovskites by using 3-chlorobenzylamine iodine, which can effectively reduce defect density and restrain ion migration. A champion efficiency of 22.22% for quasi-2D perovskite solar cells is achieved due to remarkably reduced nonradiative voltage loss and increased electron extraction. Additionally, the 2D-3D-2D perovskite solar cells also exhibit excellent thermal and humidity stabilities, retaining over 90 and 85% of the initial efficiencies after 2000 h under a heat stress of 65 °C and at air ambient of ∼50% humidity, respectively. Our results provide a general approach to tune perovskite films for suppressing ion migration and achieving high-performance perovskite solar cells.