First-principles studies of oxygen interstitial dopants in RbPbI3 halide for perovskite solar cells

Recently perovskite solar cells (PSCs) have caught much attention. Oxygen atom (O₁) and molecule (O₂) are important dopants to influence the stability of the structural, electronic and optical properties, thus the performance of PSCs. RbPbX₃-type perovskites have fantastic chemical stability and good power conversion efficiency. Here we have studied the effects of interstitial O₁ and O₂ on the structural properties, and hence the electronic structure of RbPbI₃ from first principles. We have included the van der Waals (vdW) forces into our density-functional-theory calculations. The formation of dopant level within the pristine band gap has been found when incorporating oxygen. The defect level, dominated by oxygen and iodine, is above the valence band maximum by 0.5–1.3 eV, depending on the location of the defects in the bulk. In addition, we can see the bandwidths of the defect levels are very narrow, which could trap the electron and affect the transport properties. In addition, a metallic state has been found in our calculations for interstitial oxygen molecule when there are strong O–O, O–Pb, and O–I bonds, indicating the complex nature of oxygen-doped PSCs. The comparison between the defect formation energies when doping oxygen atom and molecules is consistent with the previous report about oxygen-molecule passivation of PSCs. Our work has therefore provided important theoretical insight to the effect of oxygen dopants on the electronic structure of RbPbI₃.