Application of organic photodiodes to x-ray measurements -a feasibility study

Abstract

To elucidate the applicability of organic photodiodes (OPDs) to radiation measurements, three OPDs were fabricated, two with heterojunction structures (OPD-a and OPD-b) and one with a bulk-heterojunction structure (OPD-c). OPD-a and OPD-b have a structure of ITO/α-NPD/td-PTC/Al with a sensing area of 4 × 4mm2, while OPD-c has a 300-nm-thick mixed organic layer between α-NPD and td-PTC layers. All three OPDs showed rectifying properties under forward and reverse voltages. X-ray irradiation experiments have been carried out with these OPD devices. Results revealed that X-rays increased the output current, although some problems persisted, such as low photon-to-current conversion efficiency. When irradiating OPD-a and OPD-b with mono-energy X-rays at 20 keV, the current increased to about 6 pA from about 0.5 pA under dark conditions. The X-ray-induced current increased concomitantly with increasing X-ray intensity with some nonlinearity. Measurements of X-ray-induced current with OPD-c showed that it could yield a higher X-ray-induced current than those observed from OPD-a and OPD-v. © 2011 Atomic Energy Society of Japan, All Rights Reserved.