Stabilizing perovskite solar cells via facet-selective molecular engineering

The instability of metal halide perovskites (PVKs) is a major obstacle to the commercialization of perovskite solar cells (PSCs). While (111)-faceted PVKs exhibit inherent stability, the commonly observed coexisting (100) facets are prone to degradation. Here, we introduce tris(4-formylphenyl)amine (TFPA) into the FAPbI3 PVK. Calculations predict TFPA can preferentially bind onto the (100) facets, increasing the energy barrier for phase transition from α-FAPbI3 to δ-phase, and thus stabilizing the PVK structure. In situ grazing-incidence wide-angle X-ray scattering data show that TFPA alters crystal growth to favor (111) facets with face-on orientation. Electron microscopy characterizations reveal that TFPA predominantly localizes at grain boundaries, aligning PVK crystals and suppressing phase transition. Time-resolved terahertz (THz) emission spectroscopy identifies an additional polaron mode that enhances charge carrier transport. TFPA-doped devices achieve a record efficiency of 26.4% (certified 26.1%) for (111) facet-dominated PSCs and retain 96.5% of their initial efficiency after 1,100 h of continuous operation under 1 sun illumination at 65°C.