Barium(II)-based semiconductive coordination polymers for high-performance direct X-ray detection and imaging: Reducing the exciton binding energy via enhancing π-π interactions

High-performance and low-cost X-ray detector is crucial for medical imaging, nondestructive industrial detection and security checks. Semiconductive coordination polymers (CPs) with designable structures, tunable property and high cost-effectiveness have recently emerged as promising materials in direct X-ray detection. However, due to the strong Coulomb interactions between photogenerated electrons and holes, most of CPs often exhibit high exciton binding energies, resulting in relatively insufficient exciton dissociation as well as low photocurrent output and detection sensitivity in turn. Here, we employed the anthracene-based ligand to obtain two semiconductive CPs, {[Ba2(Hadba)4(DMF)8]·DMF}n 1 (H2adba = 4,4′-(9,10-anthracenediyl)dibenzoic acid, DMF = N, N-dimethylformamide) and [Ba(Hadba)2(DMA)4]n 2 (DMA = N, N-dimethylacetamide). Both of them can effectively convert X-ray into electrical signals. Compared with compound 1, compound 2 has a reduced Eb (44.9 meV) caused by the reinforced π-π interactions, contributing to the facilitated carrier transport, a significant enhance in mobility-lifetime product (μτ) and detection sensitivity irradiated by X-ray. Based on the optimized detection performance, we prepared a flexible 2-based composite film detector with a low detection of 1.02 μGy/s that meets the standard for medical imaging. In particular, this film-based detector achieves a high sensitivity of 137.31 μCGy−1 cm−2 and μτ product of 3.03 × 10−3 cm2 V−1, which are superior to all previously reported CP-based detectors and much higher than commercial α-Se. Simultaneously, a 5 × 5 pixelated X-ray imaging device was further constructed to show its potential application in direct X-ray detection and imaging.