Trifluoromethyl-Group Bearing, Hydrophobic Bulky Cations as Defect Passivators for Highly Efficient, Stable Perovskite Solar Cells

Solution-processed perovskite films are rich in surface defects and grain boundaries, which limits their performance and stability in photovoltaic application. Surface passivation using bulky organic cations can effectively reduce the surface defects of a perovskite film without affecting its fundamental properties. Herein, the use of hydrophobic bulky aromatic molecules, namely 4-trifluoromethyl-benzylammonium iodide/bromide (CF(3)BZA-I/Br), as defect-passivators to heal the surface defects and grain boundaries of perovskite films is introduced. Owing to the presence of the trifluoromethyl (-CF3) moieties, CF(3)BZA-I/Br-passivated perovskite films exhibit a hydrophobic surface with significantly fewer grain boundaries. By suppressing the surface and interfacial imperfections, CF(3)BZA-Br-treated perovskite solar cells achieve an outstanding power conversion efficiency (PCE) of 20.75%. The PCE improvement originates mainly from the reduction of trap states and nonradiative carrier recombination. The ultrathin hydrophobic barrier layer formed after passivation also shields the perovskite film surface from moisture ingress and environmental degradation, leading to improved stability of the devices. By optimizing the passivation conditions, the bulky CF(3)BZA-I/Br molecules could be the ideal defect passivators, with versatile applications in a wide variety of perovskite optoelectronics.

Automated summary

In this study, hydrophobic bulky aromatic molecules were used as defect-passivators for perovskite films, leading to significantly reduced surface defects and grain boundaries, and improved power conversion efficiency of solar cells. By suppressing surface and interfacial imperfections, the stability of the devices was also enhanced, showing versatile applications in perovskite optoelectronics.