Polyoxometalate‐Coordinated NDI‐Based Ternary D‐D'‐A MOFs for High‐Performance Flexible Direct X‐Ray Detection

Abstract Conventional semiconductor‐based direct X‐ray detectors face challenges including complex fabrication, high cost, and limited sensitivity. Metal–organic frameworks (MOFs) offer a promising alternative due to their tunable structures and chemical stability. Herein, a ternary donor‐donor’‐acceptor (D‐D′‐A) strategy employing polyoxometalates (POMs) to construct MOFs with multiple electron‐transfer pathways is proposed. Two MOFs (SiWCdDP and PWCdDP) are synthesized using π‐conjugated naphthalene diimide (NDI) acceptors, Cd 2+ nodes, and Keggin‐type POMs as secondary donors. Crucially, in SiWCdDP, POMs act as direct coordination nodes rather than guest fillers, forming a dense 3D framework that strengthens POM‐NDI supramolecular interactions and enhances electronic coupling. This POM‐coordinated architecture enables superior energy‐level alignment and efficient electron injection, yielding an exceptional X‐ray sensitivity of 258.0 µC Gy air −1 cm −2 and µτ of 2.55 × 10 −4 cm 2 V −1 outperforming PWCdDP. Furthermore, a flexible detector is fabricated by embedding SiWCdDP into a poly(vinylidene fluoride) (PVDF) matrix. This composite design reduces grain boundary defects and facilitates charge transport, yielding an improved X‐ray sensitivity of 577.4 µC Gy air −1 cm −2 alongside excellent mechanical robustness and environmental durability. Building on this, a 3 × 5 pixel‐array flexible detector is developed, providing a new platform strategy for advancing novel flexible direct X‐ray detectors.