Structure engineering of hierarchical layered perovskite interface for efficient and stable wide bandgap photovoltaics

Wide bandgap perovskite solar cells (PSCs) are a key component for the realization of highly efficient tandem solar cells. To simultaneously improve the efficiency and stability is still a big challenge. Herein, phenylmethylamine bromide (PMABr) is employed to modify FA_0.8Cs_0.2Pb(I_0.7Br_0.3)₃ wide bandgap perovskite films. This large cation is incorporated via a post-treatment, which induces a hierarchical layered perovskite and passivates the halide vacancies with the added Br⁻. The morphology of post-treated films is investigated with synchrotron-based techniques, revealing the formation of a layered structure at the surface, which depends upon the concentration of the PMABr solution. In particular a hierarchical microstructure is observed, consisting of a highly stable pure 2D (n = 1) perovskite layer on top of an efficient quasi-2D (n = 2) perovskite layer that caps an underlying 3D perovskite film. By precisely controlling the surface structure and thickness of the 2D perovskites, wide bandgap (~1.74 eV) PSCs reach an efficiency of 18.5% with negligible hysteresis and a stabilized efficiency of 17.9%. Furthermore, the device moisture stability is also significantly enhanced after the post-treatment, indicating that the post-treatment with PMABr is a viable processing method to achieve both efficient and stable wide bandgap PSCs.