Para-halogenated triphenyltriazine induced surface passivation toward efficient and stable perovskite solar cells

Surface passivation is a practical approach to improve the efficiency and stability of perovskite solar cells (PSCs). In this paper, we introduce para-halogenated triphenyltriazine (TRZ-X, X = F, Br, I) to modify the perovskite absorbers. As the core of TRZ-X, 1,3,5-Triazine has abundant C = N bonds, which can produce intermolecular interactions with uncoordinated Pb2+. The halogen atoms as peripheral unit of TRZ-X with strong electronegativity can not only generate ionic bonds with Pb2+ in the perovskite but also form a stable rigid plane with the TRZ group. Under the synergy effect of C = N bonds and halogen atoms, the defect density of perovskite films is effectively decreased, contributing to the power conversion efficiency (PCE) and stability of devices. Moreover, the presence of TRZ-X hydrophobic passivation layer could prevent moisture penetration, which is beneficial to long-term stability of PSCs. Due to the strong electronegativity, TRZ-F modified device presents the best PCE of 19.81% compared with that (18.32%) of control device. In addition, TRZ-F passivated and unencapsulated device retains 81% of the initial PCE after 1200 h storage under ambient condition with a relative humidity of 70%, whereas the pristine device decays to 59% of the initial PCE under the same conditions.