Speaker
Description
Junmo Yang1, Jiho Lee1, Jibum Kim1, Jungwon Kang1,2*
1. Department of Foundry Engineering, Dankook University, Yongin-Si, 16890, Gyeonggi-Do, Republic of Korea
2. Department of Semiconductor Convergence Engineering, Dankook University, Yongin-Si, 16890, Gyeonggi-Do, Republic of Korea
* Corresponding author: jkang@dankook.ac.kr
This study presents a hybrid X-ray detector combining CdSe nanoplatelets (NPLs) and PM6:Y6 organic semiconductors. While organic semiconductors offer advantages such as flexibility and low-cost manufacturing, their application in the field of X-ray radiation detection is limited due to low detection sensitivity. To overcome this problem, hybrid active layers containing inorganic nanomaterials are emerging as one of candidates for performance enhancement. The hybrid active layer forms a bulk-heterojunction (BHJ) structure optimized for efficient exciton separation and charge collection (Fig. 1a). In addition, the broad absorption spectrum of PM6:Y6 shows spectral overlap with the emission peak of the CsI(Tl) scintillator, enabling efficient photon collection (Fig. 1b). To improve the performance of the detector having a hybrid active layer, the characteristics were evaluated while varying the organic semiconductor ratio (PM6:Y6) to 1.5:1, 1:1, 1:1.5, and 1:2. Fig. 1c shows the change in detection sensitivity according to the blending ratio of PM6:Y6, and the sensitivity was 1.61 mA/Gy⁻¹ cm⁻² when the PM6:Y6 ratio was 1:1. The fabricated detectors were characterized under X-ray irradiation at 80 kVp and 63 mAs with an exposure time of 1.57 s.
The characterization of the synthesized CdSe NPLs is presented in Fig. 2a and 2b. The TEM image shows uniform CdSe NPLs with a thickness of about 2 nm, a length of about 34 nm, and a width of about 10 nm. The optical properties of CdSe NPLs exhibit absorption and emission peaks around 556 nm, which overlap with the emission spectrum of the CsI(Tl) scintillator shown in Fig. 2b. Due to this spectral match, CdSe NPLs can be applied to indirect X-ray detectors. The change in performance was tested by adding various amounts of CdSe NPLs (0, 1, 3, 5, 7 mg) to the PM6:Y6 = 1:1 ratio, which showed the best characteristics. Fig. 2c shows radiation parameters such as detector sensitivity, collected charge density (CCD), and dark charge density (DCD) as a function of changes in the content of CdSe NPLs. The highest sensitivity of 1.93 mA/Gy⁻¹cm⁻² was achieved in the hybrid detector with 5 mg of CdSe NPLs added, which is a 24.17% increase compared to the pristine detector without NPLs. Defect density and carrier mobility were evaluated using the space-charge-limited current method. As shown in Fig. 3a, the detector with 5 mg CdSe exhibited the lowest defect density of 8.21 × 1015 cm-3 and the highest mobility of 7.49 × 10-4 cm2 V-1 s-1, indicating improved charge transport and reduced recombination losses compared to pristine detector. In Fig. 3b and 3c, the changes in detection sensitivity were also evaluated according to changes in applied voltage and absorbed X-ray dose. As the applied voltage increased, the sensitivity of the hybrid X-ray detector saturated at approximately 0.8 V. At a fixed applied voltage of 0.6 V, the hybrid detector exhibited linearity with an R² value of 0.991 for the absorbed X-ray dose.
(a) (b) (c)
Figure 1. (a) The energy band diagram of the indirect X-ray detector, (b) absorbance properties of PM6:Y6, (c) blending ratio of PM6:Y6 detector with different ratio
(a) (b) (c)
Figure 2. (a) The TEM image of CdSe Nanoplatelets, (b) absorbance, emission peak of the CdSe NPLs and CsI(TI) Scintillator, (c) radiation parameters of PM6:Y6 detector with amounts of CdSe NPLs
(a) (b) (C)
Figure 3. (a) Defect density and mobility of PM6:Y6 detector with different amounts of CdSe NPLs, (b) voltage-dependent sensitivity of the PM6:Y6 detector with CdSe NPLs, (c) linear dose response of the PM6:Y6 detector with CdSe NPLs
The authors acknowledge funding from the Korea Institute for Advancement of Technology(KIAT) grant funded by the Korea Government(MOTIE) (RS-2025-02214408, HRD Program for Industrial Innovation) and National R&D Program through the National Research Foundation of Korea(NRF) funded by Ministry of Science and ICT (RS-2021NR057239)