Coordination‐Volatilization‐Induced (001) Out‐of‐Plane Reorientation by Ethylamine Hydrochloride for Efficient and Stable Inverted Perovskite Solar Cells

ABSTRACT Inverted perovskite solar cells (PSCs) offer compelling advantages in efficiency and stability. Nevertheless, the complex crystallization dynamics inherent to solution processing often result in disordered crystallographic orientations and defect accumulation. Vertically aligned grains with a preferential (001) out‐of‐plane orientation can enhance charge carrier transport and suppress nonradiative recombination. We introduce ethylamine hydrochloride (EACl) into the precursor solution. Owing to its moderate ionic size, favorable adsorption energy, and appropriate volatility, EACl first strongly coordinates with the lead‐iodide framework during film formation, promoting advanced nucleation followed by retarded crystal growth. This facilitates the formation of the α‐phase while suppressing the δ‐phase. Subsequently, the volatilization of EACl during annealing gradually induces a crystallographic reorientation of the grains, yielding a (001) predominantly preferential out‐of‐plane orientation degree of 89.89% and an average grain size of 1.17 µm. Leveraging this EACl‐based coordination–volatilization regulation strategy, the resulting PSCs achieve a power conversion efficiency of up to 26.68%. Moreover, both unencapsulated and encapsulated devices retain >90% of their initial performance after 1200 h aging at 65°C in N 2 and 1100 h continuous maximum power point tracking. This work provides new insights into the critical role of EA + in governing the crystallization kinetics and crystallographic orientation of perovskites.