Dimethylamine oxalate manipulating CsPbI3 perovskite film crystallization process for high efficiency carbon electrode based perovskite solar cells

Crystallization process determines the quality of perovskite films and the performances of resultant perovskite solar cells (PSCs). Dimethylamine oxalate has been proven as a multifunctional modulator, and is explored as an efficient additive in manipulating the crystallization process of CsPbI3 perovskite films. On one hand, oxalate serves as the precipitator that facilitates the nucleation process of intermediate. The larger size of intermediate is conductive to the larger size and smaller grain boundaries of resultant perovskite. On the other hand, in subsequent annealing process, the phase conversion and growth process of transient perovskite can be decelerated due to the strong interactions of oxalate with both dimethylamine cation (DMA+) and Pb2+. Due to the optimized crystallization kinetics, the morphology and quality of CsPbI3 perovskite films are comprehensively improved with lower defect concentrations, and charge recombination loss is effectively suppressed. Benefiting from the optimized crystal quality of perovskite films, the carbon electrode-based CsPbI3 PSCs exhibit a champion efficiency of 18.48%. This represents one of the highest levels among all hole transport layer-free inorganic perovskite solar cells.