In this paper, we attempted to improve the detection sensitivity of an indirect X-ray detector through using a hybrid active layer composed of a poly [N-90-heptadecanyl–2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT) organic semiconductor and cadmium selenide nanoplatelets (CdSe NPLs) colloidal inorganic semiconductors. First, different blending ratio in the active layer (i.e., 2:1, 1:1, 1:2 and 1:3) of PCDTBT:CdSe NPL were examined, a sensitivity of 0.057 mA/Gy∙cm2 was achieved using a 1:1 ratio due to the low series resistance (RS) and defect density in this configuration. Then, the oleic acid (OA) that was initially applied in the CdSe NPL surface was replaced with pyridine ligands, this was done because the pyridine ligand is a short-chain ligand that can help charge transfer by reducing the distance between NPLs in the active layer. In addition, an experiment was conducted to determine the optimal ligand exchange time. A detector with an PCDTBT:CdSe NPL active layer fabricated using pyridine ligand exchange achieved a sensitivity of 0.14 mA/Gy∙cm2 after an exchange time of 12 hours, this is an improvement of 155% compared to the detector using a PCDTBT:CdSe NPL with the original OA ligands. Lastly, the optimal thickness for the PCDTBT:CdSe NPL active layer was investigated. The highest mobility of 7.60 cm2/V∙s was recorded after fabricating the layer using spin-coating at 1900 rpm, the highest sensitivity of 0.20 mA/Gy∙cm2 was also achieved under these conditions. Compared to the initial state of the detector, our modifications improved the sensitivity of the PCDTBT:CdSe NPL detector by 255%.
In this paper, we report on our study of the sensitivity of an indirect-type organic X-ray detector, which depends on the conductivity of the hole-transport layer composed of PEDOT:PSS. The polar solvent, dimethylformamide (DMF), was mixed with the PEDOT:PSS solution to improve the conductivity of the HTL. When the DMF was added to the PEDOT:PSS solution, the conductive PEDOT fragments distributed more uniformly because of the high dipole moment of the DMF. In order to find the optimal process condition, the blending ratio of DMF and the baking condition of the PEDOT:PSS layer were examined. The detector with the PEDOT:PSS layer fabricated with 50 wt% DMF added and 160 °C baking for 30 min had the highest sensitivity, of 1.988 mA/Gy · cm2, which was 61.23% higher than the sensitivity of the detector with the pristine PEDOT:PSS layer.
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