Surface-anchoring fluorinated sulfonate enables efficient and stable perovskite photovoltaics

Defects in solution-processed perovskite films can trap photoinduced carriers, facilitate ion migration, and accelerate degradation of perovskites, thus posing a major threat to the performance of perovskite solar cells (PSCs). To address these issues, we rationally proposed a multifunctional sulfonium salt molecule, namely diphenyl-(trifluoromethyl)-sulfonium trifluoromethanesulfonate (TFS-TFMS), which was designed to chelate the detrimental defects of perovskite films using a cost-effective post-treatment method. Theoretical and experimental evidence indicated that defects on the surface and grain boundaries of perovskite films, including uncoordinated Pb2+, volatile organic cations and mobile ionic vacancies, were synergistically anchored by S 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 O, -CF3 and TFS+ groups in the TFS-TFMS molecule via Lewis acid-base coordination, hydrogen bonds and electrostatic interactions, respectively. The carrier dynamic behavior and energy level alignment at the interface between perovskites and hole-transportation-layers were also significantly improved. Consequently, the power conversion efficiency (PCE) of PSCs was boosted from 21.99% to 23.56% upon the introduction of TFS-TFMS, along with a diminished hysteresis index. In addition, the TFS-TFMS modified devices without encapsulation can retain 86% and 80% of their initial PCEs under aging conditions of 40-60% relative humidity (1752 h) or heating at 85 degrees C (504 h), respectively. It is expected that this synergistical design strategy of fluorine-rich sulfonium salt molecules can inspire more potential multifunctional modulators for efficient and stable PSCs towards commercialization in the future. TFS-TFMS was introduced to modulate the upper interface in n-i-p structured perovskite solar cells, resulting in significantly improved device performance owing to the synergistic engineering of fluorine and sulfonate functional sites.