Control of Organic Conformation toward 2D Hybrid Perovskites with Enhanced Thermal and Photostabilities

Two-dimensional (2D) organic–inorganic hybrid perovskites (OIHPs) have been extensively studied, as they can result in efficient and stable solar cells. However, the impact of the organic cation conformations on their properties remains under-reported. Herein, we investigate the structural effects of monosubstituting phenethylammonium spacer with a relatively large atom (e.g., bromine atom) at various phenyl ring positions in 2D lead-iodide OIHPs. Two different conformations of the organic cation are observed (i.e., gauche and anti), formed due to the steric interactions between the functional group and the ethylammonium segment. In comparison to those with anti, 2D OIHPs with gauche conformation feature organic spacers with slower dynamic behavior and stronger hydrogen-bonding interactions with the iodoplumbate frameworks. Furthermore, they exhibit relatively undistorted structures, which lead to lower bandgaps and lesser defect densities. Most importantly, the gauche conformation 2D OIHPs also demonstrate comparatively superior thermal stabilities, requiring temperatures up to 80 K higher to dissociate the organic cation as compared to those adopting anticonformations. Additionally, they manage to retain ∼80% of their photoluminescence intensity under laser illumination for 10000 s at 60% relative humidity (ca. four times higher than the anticonformation counterpart). Our work paves the way for a better design of organic spacers to be used for highly efficient and stable solar cells.