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, CuCoO₂, with excellent optoelectronic properties is successfully synthesized by precisely tunning Co³⁺/Co²⁺ 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 CuCoO₂ 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 CuCoO₂-based devices deliver high power conversion efficiencies (PCEs) of 26.70% (0.09 cm²) and 25.07% (1 cm²). 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.