A Universal Ternary Solvent System of Surface Passivator Enables Perovskite Solar Cells with Efficiency Exceeding 26

Surface passivation is a vital approach to improve the photovoltaic performance of perovskite solar cells (PSCs), in which the passivator solvent is an inevitable but easy‐ignored factor on passivation effects. Herein, a universal ternary solvent system of surface passivators is proposed through comprehensively considering the solubility and selective perovskite dissolution of the solvent to maximize the passivation effect. Tetrahydrothiophene 1‐oxide (THTO) is selected as the passivation promoter by comparing the binding energy with perovskite and the ability to distort the perovskite lattice among various aprotic polar solvent molecules, which can facilitate the passivator's reaction with perovskite and achieve sufficient passivation on perovskite surface. Besides, chlorobenzene (CB) is used as the diluting agent to minimize the amount of isopropanol (IPA), inhibiting the additional solvent‐induced defects. As a result, the planar PSCs achieve a power conversion efficiency (PCE) of 26.05%, (certificated 25.66%). Besides, the unencapsulated devices exhibit enhanced stability, which can maintain 95.23% and 95.68% of their initial PCE after 2000 h of storage in ambient air and 800 h of light‐soaking in N2‐glovebox. Moreover, this ternary solvent system also exhibits a well applicability and reliability in different passivator such as PEAI, BAI, and so on. A suitable solvent system of passivator can maximize the passivation effect, further improving the photovoltaic performance of perovskite solar cells (PSCs). This work proposes a ternary solvent system of 4‐MeO‐PEAI, which can inhibit the solvent‐induced additional defects and achieve a sufficient passivated perovskite surface simultaneously. The resulting PSCs achieve an impressive power conversion efficiency (PCE) of 26.05%, and the devices can maintain 95.23% and 95.68% of their initial PCE after 2000 h storage in ambient air and 800 h light‐soaking in N2‐glovebox.