Pyridine Derivatives' Surface Passivation Enables Efficient and Stable Carbon-Based Perovskite Solar Cells

Surface passivation has been demonstrated to be an effective strategy to reduce defects of hybrid halide perovskite films for making efficient and stable perovskite solar cells (PSCs). Especially the strong interaction between the passivation agents and the perovskite films is favorable for achieving a durable passivation effect. Pyridine derivatives with bidentate anchoring groups can interact with the uncoordinated Pb2+ and minimize perovskite defects. Herein, in order to rationally design bidentate passivation agents, the passivation effects of pyridine (Py) and its derivatives (Py-X) with different functional groups of amino, carboxyl acid, and aldehyde are compared in carbon-based perovskite solar cells (C-PSCs) for the first time. Py-NH2 is found to passivate the perovskite CH3NH3PbI3 film the best among all the passivation agents. The N atoms on both the pyridine ring and the amino group with lone pair electrons can combine with the uncoordinated Pb2+, effectively reducing the defect density in the Py-NH2 -treated perovskite film. First-principles density functional theory (DFT) calculations reveal that the strong interaction between Py-NH2 and CH3NH3PbI3 strengthens Pb-1 bond and hinders the formation of 1 vacancies. Carbon-based perovskite solar cells (C-PSCs) passivated by Py-NH2 achieve a champion power conversion efficiency (PCE) of 14.75%, compared to 11.55% of the control device. The Py-NH2 passivated C-PSCs also exhibit good long-term stability, retaining more than 90% of the initial efficiency after 30 days of storage in air with 35-45% relative humidity.