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.