Room-Temperature Molten Salt-Mediated CsPbI₃ Growth for Excellent Photovoltaic Performance

Defects within perovskite have been known to act as the nonradiative recombination centers, negatively impacting the carrier transport, which degrades the photovoltaic performance of perovskite solar cells (PSCs). Therefore, preparing a high-quality perovskite film is of vital significance. To this end, a room-temperature molten salt, dimethylamine formate (DMAFa), is introduced into perovskite precursor solution to regulate the crystallization process of CsPbI3 films. DMAFa can coordinate with Pb2+ as HCOO--Pb2+ in the early stages, then HCOO--Pb2+ is gradually displaced by I--Pb2+ due to its decomposition during the subsequent annealing, thus delaying the crystallization rate, meanwhile, the DMA(+) can interact with the uncoordinated Pb2+ to passivate defects of perovskite films, thereby, forming a high-quality CsPbI3 film with large grain size and low-defect density. As a result of this strategy, the power conversion efficiency is increased to 20.40%, and the open-circuit voltage is up to 1.21 V. These findings indicate that the introduction of DMAFa offers a fundamental way to achieve high-performance CsPbI3 PSCs.