A Versatile Molten-Salt Induction Strategy to Achieve Efficient CsPbI Perovskite Solar Cells with a High Open-Circuit Voltage >1.2 V.

All-inorganic CsPbI perovskite has emerged as an important photovoltaic material due to its high thermal stability and suitable bandgap for tandem devices. Currently, the cell performance of CsPbI solar cells is mainly subject to a large open-circuit voltage (V ) deficit. Herein, a multifunctional room-temperature molten salt, dimethylamine acetate (DMAAc) is demonstrated, which not only directly acts as a solvent for precursor solutions, but also regulates the phase conversion process of the CsPbI film for high-efficiency photovoltaics. DMAAc can stabilize the DMAPbI structure and eliminate the Cs PbI intermediate phase, which is easily spatially segregated. Meanwhile, a new homogeneous intermediate phase DMAPb(I,Ac) is formed, which finally affords high-quality CsPbI films. With this approach, the charge capture activity of defects in the CsPbI film is significantly suppressed. Consequently, a V of 1.25 V and >21% power conversion efficiency are achieved, which is the record highest reported thus far. This intermediate phase-regulation strategy is believed to be applicable to other perovskite material systems.