Rational design of multifunctional pseudohalide anions for synergistic defect passivation and suppressed ion migration in perovskite solar cells

To enhance both the efficiency and stability of perovskite solar cells (PSCs), an ideal interface needs to be formed; that is, defect passivation, efficient charge transport and suppression of ion migration must be achieved simultaneously. We rationally designed a series of multifunctional pseudohalide (PH) anions in this study, including APCA, APCA2OH, and APCA3OH, and systematically and synergistically regulated the interfacial properties by introducing functional groups such as -COO-, -OH, -NH2, -CN, and aromatic rings. First-principles calculations and ab initio molecular dynamics (AIMD) simulations indicate that the optimal APCA3OH molecule anchors to the perovskite surface via strong multidentate chelation. Cooperative coordination can reduce both deep and shallow trap states effectively by breaking up the harmful Pb3 trimers and Pb2 dimers associated with Pb-I antisite (PbI) and iodine vacancy (VI) defects. From an electronic standpoint, the intrinsic dipole moments of the designed PH anions can adjust the surface work function to reduce the energy-level mismatch at the electron-selective contact and promote non-radiative carrier extraction. In addition, the synergistic chemical bonding and prominent steric hindrance caused by the ortho-hydroxyl group in APCA3OH increase the activation energy for iodide migration to 10.72 eV and thus inhibit halide diffusion. The functionalized structure also forms a dense hydrogen-bonding network that restricts water infiltration and enhances dynamic stability. By elucidating the structure-activity relationships of these complex molecular architectures, this work provides fundamental molecular insights for the design of comprehensive interfacial passivants for future perovskite photovoltaics.