Orbital Interactions between Organic Semiconductor Spacer and Inorganic Layer in Dion-Jacobson Perovskite Enable Efficient Solar Cells.

Two-dimensional (2D) Dion-Jacobson (DJ) perovskites have become emerging photovoltaic materials owing to their intrinsic structure stability. However, as insulating aliphatic cations were widely used as spacers, the interactions between the spacers and inorganic layers in DJ perovskites have rarely been studied. Here, an organic semiconductor spacer with two covalently connected thiophene ring, namely bithiophene dimethylammonium (BThDMA), was successfully developed for 2D DJ perovskite solar cells (PSCs). An important finding is that there are strong orbital interactions between conjugated organic spacer and adjacent inorganic layers, whereas no such interactions exist in DJ perovskite using aliphatic octane-1,8-diaminium (ODA) spacer with similar length. The BThDMA spacer with multiple conjugated aromatic rings could also induce the crystal growth with large grain size and preferred vertical orientation, resulting in reduced trap density and improved charge carrier mobility. As a result, the optimized device based on (BThDMA)MA n -1 Pb n I 3 n +1 (nominal n = 5) shows an excellent PCE of 18.1% with negligible hysteresis, which is a record efficiency for 2D DJ PSCs using spacer with two or more covalently linked aromatic rings. Our findings provide a novel and important insight on achieving efficient and stable 2D DJ perovskite solar cells by developing organic semiconductor spacers. This article is protected by copyright. All rights reserved.