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 Pb 2+ 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 CsPbBr 3 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 CsPbBr 3 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 CsPbBr 3 NCs, the stable perovskite film with reduced defect is obtained, consequently promoting the efficiency up to 11.60 % for CsPbIBr 2 and 14.44 % for CsPbI 2 Br carbon-based devices, with excellent durability under harsh conditions.