Formation of DY Defect Centers in Bi-Doped Hybrid Halide Perovskites

The DX center is a major killer defect that limits the n-type doping in some four-fold coordinated semiconductors. It is a deep negatively charged defect complex converted from a nominal shallow donor defect, which can serve as a trap center of electrons, thus is detrimental to the performance of optoelectronic devices. Similar to the DX center, we find that a donor-yielded complex center (DY center) also exists in six-fold coordination semiconducting materials. For example, Bi is commonly used as n-type dopant in perovskite APbX₃. However, our first-principles calculations show that the DY centers are formed in Bi doped MAPbBr₃ when the Fermi level is high in the gap, but, interestingly, it does not form in MAPbI₃. The reason that the DY center is formed in MAPbBr₃ instead of MAPbI₃ is attributed to the high conduction band minimum (CBM) of MAPbBr₃. Our results are able to explain recent puzzling experiment observations and the thorough discussions of the formation and the properties of the DY center in perovskites provide enlightening insights to the defect study in six-fold coordinated semiconductors.