Intrinsic defects at the interface of the FAPbI₃/MAPbI₃ superlattice: insight from first-principles calculations

The use of a superlattice structure is an effective strategy to develop novel perovskites and obtain excellent light-absorbing materials. Based on first-principles calculations, we systematically studied the properties of intrinsic point defects at the interface of the FAPbI₃/MAPbI₃ superlattice. Our calculations show that charged defects are easier to form as compared to neutral ones at the superlattice interface due to low formation energies. Most defects with low formation energies have a shallow level in the band gap, and some deep level defects have high formation energies, so the superlattice perovskite exhibits high defect tolerance. Pb_I³⁺ is a dominant and detrimental defect, which acts as a non-radiative recombination center because it has low formation energy and a deep transition level. To avoid the generation of Pb_I³⁺ defects, it is suggested to synthesize FAPbI₃/MAPbI₃ superlattices under I-rich conditions. The calculated light absorption coefficients and photovoltaic performance parameters demonstrate that the presence of defects leads to a certain degree of reduction in light absorption and power conversion efficiency (PCE) of solar cells made of FAPbI₃/MAPbI₃ superlattices, but the excellent performance of the perovskite solar cell (PSC) is basically retained. The superlattice perovskites are still promising candidates for light-absorbing materials of PSCs. This study is expected to contribute to a better understanding of the properties of defects at the superlattice interface and provide theoretical support for the design of high performance PSCs.