CsPbBr3 nanocrystals as electron and ion “Reservoirs” to induce energy transfer and grain reconstruction for efficient carbon-based inorganic perovskite solar cells

Electron cloud density around the functional group of Lewis-base molecule (passivator) highly determines the interaction strength with undercoordinated Pb2+ in perovskite film. With the aim to maximize this scenario, herein, we fabricate a thermally-activated delayed fluorescence molecule (3,4,5,6-tetrakis(3,6-diphenylcarbazol-9-yl)-1,2-dicyanobenzene, 4CzPN-Ph) bound CsPbBr3 nanocrystal (NC) to heal the defective perovskite surface. Because of the suitable energy alignment, there is a Förster or Dexter triplet energy transfer process from CsPbBr3 NC donor to 4CzPN-Ph acceptor under light irradiation, leading to the increased electron density within 4CzPN-Ph molecule and thus the enhanced passivation ability. Together with the formation of compositional gradient layer owing to the halide exchange reaction with CsPbBr3 NCs, the stable perovskite film with reduced defect is obtained, consequently promoting the efficiency up to 11.60 % for CsPbIBr2 and 14.44 % for CsPbI2Br carbon-based devices, with excellent durability under harsh conditions.