Polymorph engineering for organic detectors enabling high-sensitivity and high-resolution X-ray imaging

Organic semiconductor single crystals (OSSCs) hold great promise for direct X-ray detection owing to their low cost and tissue equivalence. However, their performance is often limited by inefficient charge transport. Herein, we develop a cooling-rate-modulated polymorphic growth strategy to regulate molecular conformation and packing, yielding large single crystals of two previously unreported BMOPA polymorphs, BMOPA-α and BMOPA-β. Comparative structural and computational analyses reveal that BMOPA-β exhibits a substantially larger effective hole transfer integral than BMOPA-α, providing a direct microscopic explanation for its more efficient hole transport. The smaller deviation angle between the charge transport pathway and the intermolecular interaction axis of BMOPA-β further favors effective transport under the applied electric field, resulting in a hole mobility of 8.59 cm 2 V −1 s −1 . As a result, the BMOPA-β single-crystal detector achieves a high sensitivity of 584.4 μC Gy air −1 cm −2 , and an ultralow detection limit of 37.8 nGy air s −1 , enabling high spatial-resolution (3.47 lp mm −1 ) X-ray imaging. This work highlights molecular packing structure control via polymorph engineering as an effective strategy for improving carrier transport characteristics in organic X-ray detectors.