Competitive Coordination-Driven Phase Evolution toward Phase-Pure Quasi-2D Dion−Jacobson Perovskites with Uniform Quantum Wells

Quasi-two-dimensional (quasi-2D) Dion−Jacobson (DJ) perovskites feature bidentate diammonium cations that eliminate van der Waals gaps, providing efficient carrier transport and structural stability. However, aggressive coordination between these spacers and the inorganic framework during crystallization causes disordered quantum well (QW) distributions, severely hindering carrier transport. Herein, we present a competitive coordination-directed phase evolution strategy to achieve phase-pure quasi-2D DJ perovskites with uniform QWs. By introducing dimethylamine as a competitive ligand, Pb 2+ species are effectively captured during the initial wet-film stage, preventing the formation of undesired high-n phases. During subsequent annealing, the controlled release of Pb 2+ species enables stoichiometric reactions with pre-existing low-n phases, resulting in targeted phase-pure DJ perovskites. With the elimination of phase boundaries and a homogeneous energy landscape, our photodetectors demonstrate an impressive on/off ratio of 2.2 × 10 5, high responsivity of 4.32 A W −1, and enhanced stability, establishing a robust kinetic modulation approach for high-performance optoelectronics.