Aziridinium Lead Iodide: A Stable, Low-Band-Gap Hybrid Halide Perovskite for Photovoltaics

The low ionization energy of an A site molecule is a very important factor, which determines the thermodynamical stability of APbI3 hybrid halide perovskites, while the size of the molecule governs the stable phase at room temperature and, eventually, the band gap. It is challenging to achieve both a low ionization energy and the reasonable size for the PbI3 cage to circumvent the stability issue inherent to hybrid halide perovskites. Here we propose a new three-membered charged ring radical, which demonstrates a low ionization energy that renders a good stability for its corresponding perovskite and a reasonable cation size that translates into a suitable band gap for the photovoltaic application. We use ab initio calculations to evaluate a polymorphism of the crystal structure of the proposed hybrid halide perovskite, its stability, and electronic properties in comparison with the mainstream perovskites, such as the methylammonium and formamidinium lead iodide.