Adding to the Perovskite Universe: Inverse-Hybrid Perovskites

Perovskites are a rich family of functional materials with many interesting physical properties. Usually, they contain two cationic species on the A- and B-sites, surrounded by anionic species on the X-site, but compounds are also known that invert the ion types on the respective lattice sites (inverse perovskites). Recently, conventional perovskites with one inorganic cation substituted by an organic molecule were intensively studied due to the promising performance of CH3NH3PbI3 based solar cells. Here, for the first time, we take the concept of inverse perovskites to organic-inorganic hybrid materials, investigating the properties of inverse-hybrid perovskites by first-principles calculations, adding yet another structural variant to the perovskite universe. We present results for various compositions with a wide range of band gaps from metallic systems over small and intermediate band gaps to large band gap semiconductors. Due to the changed location of the organic ion, the inverse structure could overcome stability problems of current hybrid perovskite photovoltaics. In addition, inverse-hybrid perovskites show inherent off-center displacement of ions, leading to polar phases with large polarization.