Efficient and Stable Carbon-Based Perovskite Solar Cells via Passivation by a Multifunctional Hydrophobic Molecule with Bidentate Anchors

Surface passivation has demonstrated to be an effective strategy to improve the power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). Passivation treatment can effectively reduce the density of defect states at the surface and grain boundaries of perovskite films. Herein, a passivation agent of 2-amino-5-(trifluoromethyl)pyridine (5-TFMAP) with bidentate groups is applied to passivate perovskite CH3NH3PbI3 films for the first time. Two types of electron-rich nitrogen atoms from both the pyridine ring and the amino group provide strong interaction with the under-coordinated Pb2+. Additionally, the trifluoromethyl group offers a hydrophobic property and improves moisture stability of the as-fabricated PSCs. It is found that the 5-TFMAP passivation layer can effectively reduce the defect states, promote better carrier transport, and suppress non-radiation recombination of the perovskite films. The best PCE of carbon-based PSCs passivated by the 5-TFMAP agent achieves a high efficiency of 14.96% compared with that of 11.90% for the control PSCs. Moreover, the long-term stability of PSCs with the 5-TFMAP passivation treatment is greatly improved, and its PCE can maintain 80% of its original PCE after being stored for 1200 h with a relative humidity of around 35% at room temperature.