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

摘要

Solution-processed perovskite films are rich in surface defects and grainboundaries, which limits their performance and stability in photovoltaicapplication. Surface passivation using bulky organic cations can effectivelyreduce the surface defects of a perovskite film without affecting its fundamentalproperties. Herein, the use of hydrophobic bulky aromatic molecules, namely4-trifluoromethyl-benzylammonium iodide/bromide (CF_3BZA-I/Br), as defectpassivatorsto heal the surface defects and grain boundaries of perovskite filmsis introduced. Owing to the presence of the trifluoromethyl (-CF_3) moieties,CF_3BZA-I/Br-passivated perovskite films exhibit a hydrophobic surface withsignificantly fewer grain boundaries. By suppressing the surface and interfacialimperfections, CF_3BZA-Br-treated perovskite solar cells achieve an outstandingpower conversion efficiency (PCE) of 20.75%. The PCE improvement originatesmainly from the reduction of trap states and nonradiative carrier recombination.The ultrathin hydrophobic barrier layer formed after passivation also shields theperovskite film surface from moisture ingress and environmental degradation,leading to improved stability of the devices. By optimizing the passivationconditions, the bulky CF_3BZA-I/Br molecules could be the ideal defect passivators,with versatile applications in a wide variety of perovskite optoelectronics.