Bi(trifluoromethyl) Benzoic Acid-Assisted Shallow Defect Passivation for Perovskite Solar Cells with an Efficiency Exceeding 21%

Chemical additive engineering is reported to be a simple yet effective approach to passivate shallow defects at the surface and grain boundaries, restrict nonradiative recombination losses, and further enhance the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, we successfully introduce a small organic molecule 3,5- bis(trifluoromethyl)benzoic acid (6FBzA) into an antisolvent as a shallow defect passivator for perovskite films. The Pb2+ defects at the surface are greatly healed due to the coordination interaction of carbonyl and fluorine groups of 6FBzA with Pb2+. Consequently, the trap-assisted nonradiative recombination is effectively suppressed, as well as the interfacial charge extraction and transfer is significantly enhanced. As a result, the 6FBzA-treated PSC obtains a champion PCE of 21.09% with negligible hysteresis, which is obviously superior to the reference device (18.45%). Furthermore, on account of the high hydrophobicity of 6FBzA, the unencapsulated 6FBzA-treated device exhibits a good long-term stability, maintaining 82% of its initial PCE at a relative humidity of 30-40% in ambient air after 1800 h of aging.