Understanding of the formation of shallow level defects from the intrinsic defects of lead tri-halide perovskites

Organic-inorganic hybrid perovskites have unique electronic properties in which deep level defects are rarely formed. This unique defect characteristic is the source of the long carrier diffusion length. This theoretical study shows what causes this characteristic formation of shallow level defects in lead tri-halide perovskites. Comparative studies between iodides and other halides showed that deep level defect states were generated for Cl based perovskites. Longer Pb-halide bond lengths and narrower band gaps are beneficial for preventing deep level defect states. Additionally, our study shows that the formation of shallow level defects does not change even when the lattice structures of the perovskites do not reach their equilibrium structures. For the organic-inorganic hybrid perovskites, the longer Pb-halide bond distance and the smaller band gap are the key factors to determine the shallow level energy formation of the intrinsic defects.