Orientation and mobility control of 4HCB organic film for flexible X-ray detectors with high performance

Abstract

• The space-confined melt process is used to produce highly orientated organic semiconducting crystalline films with a large area. • Confined molecular packing significantly improves the hole mobility. • The 4HCB based X-ray detectors can achieve a high sensitivity with low dark current, result in outstanding direct imaging capabilities. • The device shows steady flexibility, with no degradation in detecting function after 100 cycles of bending. In comparison to inorganic counterparts, organic semiconducting (OSC) crystalline films are promising for building large-area and flexible ionizing radiation detectors for X-ray imaging or dosimetry due to their tissue equivalence, simple processing and large-scale production accessibility. Fabrication processes, however, hinder the ability to generate aligned and large-area films with high carrier mobility. In this work, the space-confined melt process is used to produce highly orientated 4HCB (4-hydroxycyanobenzene) OSC films with a large area of 15 × 18 mm 2 . The out-of-plane direction of the 4HCB film is <001>, and the benzene rings are found to be extensively overlapped inside the in-plane direction, according to the XRD patterns. The film exhibits a high resistivity up to 10 12 Ω cm, and high hole mobility of 10.62 cm 2 V −1 s −1 . Furthermore, the 4HCB (80-μm-thick film) based X-ray detectors can achieve a sensitivity of 93 μC Gyair −1 cm −2 and on/off ratio of 157. The device also shows steady flexibility, with no degradation in detecting function after 100 cycles of bending. Finally, the proposed 4HCB film detectors demonstrated a high-resolution X-ray imaging capability. The imaging of several materials with sharp edges (copper and polytetrafluoroethylene) has been obtained. This work has developed a fast but efficient approach for producing large-area, highly oriented OSC films for high-performance X-ray detectors.