A multiple-coordination framework for CsPbI₂Br perovskite solar cells

Though rapid advancement has been made in inorganic perovskite solar cells (PSCs), the lower efficiency in comparison with their organic-inorganic counterparts hinders their progress towards commercialization. The inevitable trap defects existing in the charge transport layers and the perovskite absorber are the main obstacles to superior performance. Herein, a composite approach by incorporating choline zwitterions into the electron transport layer (ETL) and the CsPbI2Br perovskite layer simultaneously for high-efficiency CsPbI2Br PSCs is proposed. Effective interfacial charge extraction is engineered by forming an intermolecular framework via multiple-coordination of choline chloride (ChCl) with the uncoordinated Sn2+ in the ETL and the uncoordinated Pb2+ in the CsPbI2Br film. In addition, the zwitterionic ChCl can coordinate with the negatively charged defects in the CsPbI2Br film, resulting in the charge neutralized passivation of trap defects. Thus, the non-radiative recombination is significantly suppressed. As a consequence, the open-circuit voltage is increased from 1.199 V to 1.315 V, leading to a high efficiency of 17.06% for the inorganic CsPbI2Br PSCs.