Anisotropic Growth of Centimeter‐Size CsCu 2 I 3 Single Crystals with Ultra‐Low Trap Density for Aspect‐Ratio‐Dependent Photodetectors

Low-dimensional ternary copper iodide metal halide with strong quantum confinement effects has made great progress in optoelectronic fields. However, efficient regulation of anisotropic growth of metal halides single crystal still remains a great challenge. Herein, 2 cm size CsCu2 I3 single crystals with tunable aspect ratio and the trap states (ntrap ) as low as 5.38 × 109 cm-3 are fabricated by optimized anti-solvent vapor-assisted method, in which the growth cycle is shortened by half. Evidenced by real-time observation and the LaMer growth model, the rapid and anisotropic growth mechanism is ascribed to preferential 1D growth, promoted by high concentration and fast vapor rate. Furthermore, the aspect-ratio-dependent optoelectronic performance is observed, the on-off ratio for 2 cm CsCu2 I3 single crystal are enhanced 350 times compared with those of short and thick single crystal, which shows ultrahigh on-off ratio of 1570, D* of 1.34 × 1012 Jones, Rλ of 276.94 mA W-1 , t rise /t decay of 0.37 and 1.08 ms, and EQE of 95.53%, which are clearly at very high level among lead-free perovskite-based photodetectors. This study not only provides a new strategy for overcoming anisotropic growth limitations of low-dimensional metal halides, but also paves a way for high-performance optoelectronic applications.