Passivation effect of theophylline on the surface defects of MAPbI3 perovskite

Employing molecular passivators to reduce defect density of perovskite surface is an effective way to improve the stability and photovoltaic performance of perovskite solar cells. Herein, the passivation effect and mechanism of theophylline molecule on the defects of MAPbI3 (0 0 1) surface were investigated by first-principles calculations based on density functional theory. Our results reveal that the theophylline can stably absorb on the MAPbI3 surface. Two passivation modes: defect-inhibiting mode and defect-healing mode, are proposed to describe the passivation mechanism. In the defect-inhibiting mode, the theophylline adsorbed on the MAPbI3 surface leads to the increase of formation energies of most defects, suppressing the generation of defects. In the defect-healing mode, the adsorption of theophylline on the defect site of MAPbI3 surface can effectively eliminate or weaken the defect impurity states in the bandgap, consequently healing the defects. Hence, incorporating theophylline molecule into MAPbI3 perovskite film is an effective strategy to passivate surface defects and improve the stability and performance of perovskite solar cells.