Gradient Facet Orientation Engineering Via Mg ₃ Sb ₂ Quantum Dots for High‐Performance and Stable Perovskite Solar Cells

ABSTRACT Organic‐inorganic hybrid perovskite suffers from uncontrollable crystallization in solution processing, leading to the formation of randomly oriented polycrystalline films and thus limiting both performance and stability of perovskite solar cells (PSCs). Here, we propose a Mg ₃ Sb ₂ quantum dots (QDs) post‐treatment method on perovskite wet film to modulate perovskite crystallization and guide facet‐specific growth. As a result, high crystallization quality perovskite films with gradient facet orientation (GFO) are constructed. The GFO structure with (111) facet‐dominated top layer and (001) facet‐dominated bottom layer synergistically integrates the advantages of different crystal facets, i.e., low work function, high ion migration activation energy, high hole mobility, and superior stability against moisture of (111)‐facet, and low electron trap state density and high electron mobility of (001)‐facet. Moreover, Mg ₃ Sb ₂ QDs inhibit the formation of I ⁻ vacancy defects by Mg ²⁺ strongly interacting with perovskite. Consequently, the optimized target PSCs achieve a champion power conversion efficiency (PCE) of 25.18% (vs. 23.07% for control device). The unencapsulated devices exhibit significantly improved stability, retaining 75% of its initial PCE after continuous light soaking for 1000 h and over 75% after storage in the dark for 6240 h. The corresponding flexible PSCs obtain a champion PCE of 24.03% and exhibit excellent mechanical durability.