Liquid Ga nanodroplet-templated heteroepitaxy of MAPbI3 for high-efficiency printable mesoscopic perovskite solar cells.

Precise control over microstructure and crystallinity of perovskite films is pivotal for achieving high-performance solar cells. However, realizing large-grained and preferentially oriented perovskite crystals remains particularly challenging in printable mesoscopic architectures. Herein, we present a liquid-metal-enabled heteroepitaxial strategy to regulate MAPbI₃ crystallization on Ga₂O₃ surfaces derived from Ga nanodroplets. Structural modeling and atomic-resolution transmission electron microscope (TEM) analysis reveal an exceptional lattice match between the (110) planes of MAPbI₃ and the exposed Ga₂O₃ facets, with an ultralow mismatch of merely 0.32 %. This near-perfect lattice alignment drives the formation of orientation-controlled MAPbI₃ crystals within the mesoporous scaffold. Moreover, the epitaxial interface establishes type-II band alignment that accelerates charge extraction while suppressing interfacial recombination. The resultant printable mesoscopic perovskite solar cells achieve a champion power conversion efficiency (PCE) of 20.2 % (AM1.5G), representing a 16 % enhancement over conventional non-epitaxial counterparts. Crucially, the devices demonstrate exceptional operational stability, retaining 97 % of initial PCE after 3000 h of maximum power point tracking under harsh conditions (55 ± 5 °C, 85 % RH).