Chemical Equilibrium Modulated Crystallization of 2D Perovskite Single Crystals for High‐Performance and Robust Dual‐Mode Photonic Detection

ABSTRACT 2D perovskites, characterized by distinctive quantum‐well structure and high exciton binding energy, offer unprecedented opportunities for photonic detection. However, synergistically driving efficient carrier extraction and rapid radiative recombination within monolithic single crystals (SC) remains a fundamental challenge. Herein, a room‐temperature chemical equilibrium‐modulated crystallization strategy is demonstrated to synthesize centimeter‐scale 2D (PA) 2 PbBr 4 (PPB) SCs. The use of a hygroscopic acid‐base reactive agent precisely regulates the solvent evaporation kinetics, suppressing stochastic nucleation and yielding high‐quality SCs with suppressed light scattering. Consequently, planar PPB photodetectors (PDs) exhibit a notable and robust UV response, featuring a large on/off ratio of 2.77 × 10 4 , a wide linear dynamic range of 159 dB, and an ultra‐low limit of detection of 3.5 nW cm −2 . Simultaneously, the intense exciton confinement endows the PPB SCs with strong radioluminescence and robust radiation stability. Both SCs and flexible film scintillators demonstrate excellent practical x‐ray imaging capabilities. Crucially, the absence of grain boundaries inherently mitigates internal light scattering, enabling SC scintillators to achieve an impressive spatial resolution up to 26.5 lp mm −1 , representing one of the highest values among the reported metal halide SC scintillators. This work establishes a kinetically control for high‐quality SCs synthesis and provides valuable insights for high‐performance and robust dual‐mode photonic detection.