Passivation of surface defects in FAPbI3 perovskite by methimazole molecule: A first-principles investigation

There are a large number of defects existing on the surfaces and grain boundaries of perovskite film, which cause the reduction of power conversion efficiency and accelerate the degradation of solar cell devices. Herein, based on the first-principles of density functional theory calculations, we proposed two defect passivation modes, defect-inhibiting mode and defect-healing mode, to explore the passivation effect and mechanism of methimazole (MMI) molecule on the surface defects of formamidinium lead triiodide (FAPbI3). Our calculations show that MMI molecule can stably adsorb on the FAPbI3 (0 0 1) surface by forming Pb−S coordination bond and I···H hydrogen bond. In the defect-inhibiting mode, the chemical statuses of under-coordinated Pb and I ions on the perovskite surfaces are alleviated by the MMI adsorption, leading to the increase of defect formation energy and thus inhibiting the formation of surface defects. In the defect-healing mode, the S atom in MMI molecule provides its lone pair electrons to fill the defect states introduced by the surface defects, eliminating or reducing the defect states near the band edge or in the bandgap. This study gives a deep understanding for the passivation mechanism of small organic molecule on the surface defects of perovskite and provides an effective strategy of surface passivation for improving the performance of perovskite solar cells.