Symmetrical dicyano-based imidazole molecule-assisted crystallization and defects passivation for high-performance perovskite solar cells

Benefiting from the simple and low-cost fabrication of the one-step anti-solvent spin-coating process, the perovskite solar cells (PSCs) have a boost development. However, a great number of defects are generated during solution-fabrication process, retarding the development of PSCs seriously. In this study, the utilization of 4,5-dicyanoimidazole (DCI) as an additive for perovskite precursor solution was investigated. The presence of the double –CN groups in DCI facilitated the formation of Lewis acid-base coordination with unsaturated Pb²⁺ ions, as well as interaction with I^- anions by the –NH- moiety, resulting in the enhanced perovskite film crystallinity, the reduced grain boundaries, and a significant reduction in the defects density of the perovskite film. The decreased trap-assisted recombination and voltage open circuit (V_OC) losses in the PSC resulted in the improved photovoltaic performance of device treated by DCI molecule, the PCE increased from 19.59 % to 21.87 % significantly. Moreover, the unencapsulated device with DCI additive exhibited a remarkable 87.8 % retention of its initial PCE after exposure under 10–20 % relative humidity for 60 days, demonstrating an excellent stability than control device.