Response of organic photodiode fabricated directly on plastic scintillator to X-rays

Organic photodiodes (OPDs) have attracted considerable interest in the field of photonic devices because they are useful for large and flexible photodetectors. To assess their applicability to radiation measurement, the authors have been studying their response to X-ray irradiation. For a previous study, OPDs with a bulk heterojunction structure were fabricated. Then, their response to X-rays was evaluated. However, the X-ray-induced current was extremely low and the necessity to increase the efficiency was apparent. In this study, to increase X-ray-induced current, the authors fabricated OPDs directly on plastic scintillator plates. The device structure was a plastic scintillator substrate (1 or 5 mm)/ITO (150 nm) or IZO (100 nm)/PEDOT: PSS (30 nm)/P3HT:PCBM (200 nm)/Al (70 nm). The fabricated devices were irradiated with X-rays. Then their responses were evaluated. Results demonstrated that the X-ray-induced current can be increased by fabricating OPDs directly on plastic scintillator plates. The measured energy responses of the devices were compared with the energy deposition calculated using EGS5 code. Both results show coincident tendencies. However, because the collected charges were smaller than expected from simulations in the low-energy region, further study should be conducted to specify the factors.