Solvent-Regulated Surface Passivation for Efficient and Stable Inverted Perovskite Solar Cells

Phenethylammonium iodide (PEAI) is widely used to passivate undercoordinated ionic defects and regulate the near-surface structure of inverted perovskite solar cells; however, the solvent used for PEAI deposition can also interact with the underlying perovskite and therefore determine the treatment outcome. Here, ethanol (EtOH), isopropanol (IPA), and n-butanol (n-BuOH) were compared as aliphatic alcohol solvents for the PEAI post-treatment of inverted p–i–n solar cells based on a mixed-cation, mixed-halide Cs0.05(FA0.95MA0.05)0.95Pb(I0.95Br0.05)3 absorber. EtOH caused pronounced surface disturbance and substantially reduced device performance. IPA afforded the highest initial power conversion efficiency (PCE) of 21.92% but was accompanied by a stronger PbI2 diffraction signal. In contrast, n-BuOH provided a milder treatment, producing a comparable PCE of 21.83%, a weaker PbI2 signal, and the highest water contact angle. After dark storage in air at 25 °C and 25% relative humidity for 168 h, the unencapsulated n-BuOH-treated devices retained 82% of their initial PCE, compared with 77% for the Control. These results demonstrate that the PEAI processing solvent is an active component that governs the balance among defect passivation, surface reconstruction, initial efficiency, and short-term storage stability.