A Versatile Molten-Salt Induction Strategy to Achieve Efficient CsPbI 3 Perovskite Solar Cells with a High Open-Circuit Voltage >1.2 V.

All-inorganic CsPbI 3 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 3 solar cells is mainly subject to a large open-circuit voltage (V OC ) 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 3 film for high-efficiency photovoltaics. DMAAc can stabilize the DMAPbI 3 structure and eliminate the Cs 4 PbI 6 intermediate phase, which is easily spatially segregated. Meanwhile, a new homogeneous intermediate phase DMAPb(I,Ac) 3 is formed, which finally affords high-quality CsPbI 3 films. With this approach, the charge capture activity of defects in the CsPbI 3 film is significantly suppressed. Consequently, a V OC 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.