Synchronous regulation of bulk and interfacial defects by an ionic liquid for efficient and stable perovskite solar cells

Charge recombination at grain-boundary interfaces and charge extraction loss at perovskite-carrier transport layer interfaces are the two main causes for the performance deficiency in perovskite solar cells. Herein we reported the synthesis of an ionic liquid compound 9-bromo-6,7-diphenylpyrido[2,1-a]isoquinolin-5-ium hexafluorophosphate (DPPIQ⁺PF₆⁻), which can synchronously react with perovskites at these two essential interfaces. Specifically, the PF₆⁻ anions are incorporated into the perovskite film bulk, immobilizing organic amine ions via hydrogen bonding, while the DPPIQ⁺ cations are mainly accumulated at the top film surface, binding the [PbI₃]⁻ through anion-π interactions. Reduced defect density and improved energy level alignment are achieved in the resultant perovskite solar cells. The best-performing DPPIQ⁺PF₆⁻ incorporated device shows a high power conversion efficiency of 23.41% and demonstrates 90% efficiency retention upon maximum-power-point tracking for 1260 h under continuous one-sun-intensity illumination.