Diffusion‐Dominated Crystallization in Microchannels for 2D RP Perovskite Microwire Arrays With Pure <i>n</i> Values

ABSTRACT Phase‐pure 2D layered metal‐halide perovskites can reduce phase heterogeneity and associated energy/charge‐transfer losses, but solution processing typically produces mixed multiple‐quantum‐well phases ( n &gt; 2) owing to evaporation‐driven convection and local off‐stoichiometry. Here, we develop a microchannel‐structured template induced assembly engineering to fabricate phase‐pure BA 2 MA n−1 Pb n I 3n+1 microwire arrays with programmable n (1–6). The confined space improves uniform distributions of each component in the precursor solution by suppressing convection and enhancing diffusion‐limited mass transport, thereby avoiding the deviation from the stoichiometric ratio. Photoluminescence measurements show uniform, single‐peak emission consistent with high phase‐purity of microwires. The photodetector based on n = 6 microwire array achieves record performances with a responsivity of 1.039 × 10 4 A/W, an ON/OFF ratio of 10 5 , and fast response times of 65/215 µs, enabling real‐time heartbeat monitoring. This strategy offers a robust platform for the controlled crystallization of layered perovskites and scalable fabrication of high‐performance and high‐fidelity device arrays.