Diffusion-Dominated Crystallization in Microchannels for 2D RP Perovskite Microwire Arrays With Pure n Values

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 > 2) owing to evaporation-driven convection and local off-stoichiometry. Here, we develop a microchannel-structured template induced assembly engineering to fabricate phase-pure BA₂MA_n−1Pb_nI_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 × 10⁴ A/W, an ON/OFF ratio of 10⁵, 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.