Sensitivity improvement of quantum dot-blended hybrid detector for X-ray imaging

Abstract

This study investigated the characteristics of an indirect-type hybrid X-ray detector with a conjugated polymer poly(3-hexylthiophene) (P3HT) and CdSe quantum dot (QD) blended active layer. To improve detection sensitivity, the optimal blending ratio of P3HT:CdSe QDs, ligand exchange effect, and optimal process condition of the active layer were examined. The detector with a P3HT:CdSe QDs = 1:5 blended active layer showed the highest collected charge density (CCD) and highest sensitivity under X-ray irradiation. The replacement of a trioctylphosphine (TOP) ligand by a pyridine ligand effectively assisted the charge transport and reduced the QD aggregation, increasing the detection sensitivity of the detector by 75% after the ligand exchange. To further improve the sensitivity of the proposed detector, the optimized process conditions of the active layer were studied. The sensitivity of the detector with an active layer of about 80 nm thickness formed by a double-coating method showed the highest CCD of 62.5 nA/cm2, and the highest sensitivity of 0.14 mA/Gycm2. Due to additional pyridine treatment between the double-coating processes, the surface roughness of the active layer decreased, and the CCD and sensitivity subsequently increased.