Heterogeneous‐Nucleation and Epitaxial‐Growth of Perovskite Enabled by Delafossite‐Type Hole Transport Materials for High‐Performance Solar Cells

The quality of perovskite films deposited on inorganic hole transport materials (HTMs) have long restricted the performance of corresponding devices. Herein, a novel delafossite‐type HTM, CuCoO 2 , with excellent optoelectronic properties is successfully synthesized by precisely tunning Co 3+ /Co 2+ ratios, achieving a hole concentration three orders of magnitude higher than that of other delafossite‐type materials. The reduced Gibbs‐free energy and a nearly perfect lattice matching between the octuple distance of the (110) plane in CuCoO 2 and triple spacing of the (100) plane in formamidinium‐based perovskites promote the heterogeneous‐nucleation and epitaxial‐growth of perovskite films, resulting in a semi‐coherent interface. Consequently, high‐quality perovskite films are obtained with ordered orientation, reduced defect density, and released residual strain. The champion CuCoO 2 ‐based devices deliver high power conversion efficiencies (PCEs) of 26.70% (0.09 cm 2 ) and 25.07% (1 cm 2 ). The unencapsulated devices maintain 96.7%, 90.8% and 94.1% of their initial PCEs after long‐term storage, continuous thermal‐aging, and light‐soaking, respectively.