Modulation of Crystal Plane Growth for Efficient and Stable Perovskite Solar Cells

Achieving accurate manipulation over perovskite crystal orientation and phase purity is pivotal for realizing efficient and durable perovskite solar cells. Despite the unique advantages of lead iodide (PbI 2 ) template in the two‐step deposition process for obtaining high‐quality perovskite films, challenges remain in guiding the preferential growth of perovskite crystals due to complex facets of PbI 2 . Herein, highly crystalline PbI 2 with complete (001)‐preferred orientation has been attained by incorporating 2‐phenoxyacetamidine hydrochloride (PhOAaCl), which proficiently minimizes the crystal plane energy. This rationally architectured PbI 2 template orchestrates coherent crystal plane growth of subsequent perovskite with markedly suppressed defect density and exceptional phase purity. Moreover, we further elucidate underlying growth mechanism prevailing at the solid–liquid interface between PbI 2 and organic amine salts from integrated thermodynamic and kinetic perspectives. Consequently, the target photovoltaic device attains a champion efficiency of 26.47%. Notably, the unencapsulated devices exhibit significantly outstanding damp‐heat endurance and operational robustness, while attaining 91% of initial efficiency after 2500 h of maximum power point tracking under persistent illumination in ambient conditions.