Green‐Solvent‐Grown Perovskite Single Crystals With Suppressed Defect Densities for Superior Photo‐ and X‐Ray Detection

Achieving environmentally sustainable synthesis of high‐quality metal halide perovskite single crystals (MHP‐SCs) is critical for advancing next‐generation optoelectronic devices. The constrained solvent choices within the green chemistry framework pose a significant challenge to the fine control of crystallization pathways required for the growth of perfect MHP‐SCs. Here, we introduce a new paradigm for crystallization control based on steric hindrance engineering using a quantitatively validated green solvent system with high GlaxoSmithKline green solvent scores. We demonstrate that the steric bulkiness of solvent molecules, rather than donor number alone, plays the dominant role in governing the coordination strength between Pb 2+ and solvent, thereby regulating precursor complex stability and crystallization kinetics. Finely tuned steric environments promote the unprecedented fast growth of MAPbI 3 SCs with a record‐low trap density (2.56 × 10 8 cm −3 ) and narrowest x‐ray diffraction linewidth of 0.00802° (28.9″). These defect‐suppressed MAPbI 3 SCs enable photodetectors with an ultrahigh specific detectivity of 6.8 × 10 13 Jones and x‐ray detectors with a low detection limit of 3.6 nGy air s −1 . The steric hindrance engineering strategy proves universal across perovskite compositions. This work establishes a sustainable, scalable platform for the growth of high‐quality MHP‐SCs using quantitatively green solvents.