Sterically gated Lewis acid and base pairs enable orthogonal defect passivation in perovskite solar cells

Charged point defects cause efficiency loss and instability in perovskite solar cells. Although Lewis acids and Lewis bases individually passivate anionic and cationic defects, they are known to react with one another. As a result, introducing different combinations to solar cells forms quenching adducts that fail to provide the necessary passivation. Here we report chemically orthogonal Lewis acid and Lewis base families that enable concurrent passivation of targeted ionic defects by weakening mutual interactions. We found that bulky sp³-phosphine bases, which fail to react with fluorinated aromatic acids, can suppress Lewis acid-base orbital overlap. This strategy is effective because surface defect sites are more sterically accessible to each passivator than the two passivators are to one another. Spectroscopic and defect-profiling measurements support the additive suppression of traps, resulting in devices with power conversion efficiencies up to 27.4% (certified steady state of 25.8%).