Asymmetric Small Molecule as Interface "Governor" for FAPbI 3 Perovskite Solar Cells.

Delicate interface modification is necessary for improving the photovoltaic performance of a perovskite solar cell (PSC). Herein, two asymmetric small molecules, termed BTD-DA and BTD-PA are designed and synthesized to govern the perovskite/Spiro-OMeTAD interface. The molecule BTD-PA featuring a donor-acceptor-acceptor (D-A-A') configuration shows a larger molecule dipole and a better effect on defect passivation and energy level regulation through the strong interaction between the pyridine group in BTD-PA and the surficial uncoordinated Pb 2+ . Consequently, the PSCs based on the BTD-PA treatment harvest a champion power conversion efficiency (PCE) of 24.46% for a 0.09 cm 2 active area and 22.46% for the 1 cm 2 device. Moreover, the long-term stability of FAPbI 3 PSCs is also significantly improved because of the enhanced hydrophobicity and the inhibited phase transition of the FAPbI 3 film with BTD-PA treatment. Our research provides a new strategy for interfacial engineering to boost the PCE and stability of the FAPbI 3 PSCs.