Intrinsic point defects in halide double perovskite Cs2NaBiCl6 insight from first-principles

Highlights: • The chemical potential region of stable growth of Cs2NaBiCl6 was obtained. • The conditions for the formation of main defects in perovskites are identified. • Classification of deep and shallow level defects in a defect transition energy diagram. Various lead-free perovskite materials have recently been studied as optoelectronic materials. As one of the most promising double halide perovskite materials, Cs2NaBiCl6 has been widely studied, however, the stability and native defects have been seldom reported. It is known that the stability and native defects have a seriously effect on the electronic and optical properties. In this paper, the formation energy, transition energy levels and electronic structures of Cs2NaBiCl6 with different native defects have been investigated by first principles calculations. And the chemical potential region of Cs2NaBiCl6 is calculated, which is confined to a tiny area. Two typical chemical potentials are studied in this paper, e.g., Cl-poor and Cl-rich environments. It is found that donor defect VCl can exist stably in Cl-poor condition; however, a deep level will produce the recombination of electrons and holes, which is inconducive to the application of optoelectronic devices. In Cl-rich condition, the acceptor defects VBi and ClBi with shallow level would be dominant, which leads to p-type conduction. Moreover, this condition will suppress the defect VCl. It is thus necessary to increase the abundance of chlorine source to avoid deep level defects as well as the degradation of the properties of optoelectronic materials. Hence, this research provides a theoretical guidance for the synthesis of Cs2NaBiCl6 in favor of photoelectric materials in the experiment.