Ionic liquid reducing energy loss and stabilizing CsPbI2Br solar cells

Development of inorganic metal halide perovskites solar cells (PSCs) has been hampered by the inherent phase instability of inorganic perovskites. Herein, an ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) is proposed to stabilize the CsPbI2Br phase and reduce the surface defect density. From experimental analyzes and density functional theory calculations, the BMIMBF4 interlayer could reduce the energy loss and stabilize the cubic -phase of CsPbI2Br. The interaction between BMIMBF4 and CsPbI2Br could improve the perovskite film quality and the interfacial charge transport. Accordingly, the BMIMBF4-modified device enables a 37.18% and 18.89% improvement in the power conversion efficiency and open-circuit voltage compared to the control CsPbI2Br device, along with an 86.9% retaining of its initial performance over 1000 h storage in N2 atmosphere, while the control device drops to zero in 200 h. The work provides a novel cogitation for the defect passivation and energy loss reduction to improve both the stability and efficiency of inorganic perovskite solar cells.