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(+)PF(6)), 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-p interactions. Reduced defect density and improved energy level alignment are achieved in the resultant perovskite solar cells. The best-performing DPPIQ(+)PF(6) 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.