Dimensionality Controlling of Cs₃Sb₂I₉ for Efficient All‐Inorganic Planar Thin Film Solar Cells by HCl‐Assisted Solution Method

Abstract Since lead halide perovskite suffers from the obstructions of lead and stability, researchers recently pay more attention to the development of lead‐free and stable perovskite absorbers. A typical lead‐free antimony iodide perovskite (AIP) is synthesized through vapor reaction at high temperature for photoactive phase. Herein, hydrochloric acid is developed as an intermediate coordinated additive for Cs₃Sb₂I₉ photoactive layered phase using HCl‐assisted solution method. The uniform and highly crystalline Cs₃Sb₂I₉ layered film is obtained by antisolvent engineering. Isopropanol antisolvent is more suitable for present system comparing with traditional lead iodide perovskite‐based ones. Physical characterizations manifest the lower trap density, doubled carrier mobility, and improved junction quality from the new developed absorber film and its corresponding devices comparing with its dimer phase. Utilizing TiO₂/AIP/Au all‐inorganic structure, the champion device demonstrates a power conversion efficiency (PCE) of 1.21%, which is the top value for all‐inorganic AIP solar cells. The nonencapsulated device exhibits negligible loss in the PCE under ambient environment with 50% humidity after 60 days storing. The obtained results portray important progress toward the understanding of reliable HCl‐assisted solution method and realization of highly stable AIP solar cells.