Radiation Effects in Electret Organic Thin-Film Transistors Due to High Flux and High Dose X-Ray Irradiation.

Abstract

Organic electronic devices offer lightweight, flexible, and low-cost alternatives to conventional semiconductor technologies, with growing interest in dosimetry applications. An organic thin-film transistor (OTFT) with a polymer electret is presented for high dose-rate synchrotron dosimetry. The OTFT operates in accumulated-dose and real-time readout modes and demonstrates excellent linearity with various beam filtrations. Device response increases with decreasing energy, and simulations reveal gold contacts as the primary source of energy dependence. Depth dose measurements show good agreement with a commercial detector, validating dosimetric performance. Minimal changes in mobility are observed at clinically relevant doses, but mobility degradation becomes apparent after high accumulated doses, indicating radiation damage in active materials. X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) techniques are employed to analyze pristine and irradiated active material films separately and in a combined stack. XPS reveals oxidation in pentacene and a Fermi level shift in polystyrene in irradiated films, both of which likely cause the mobility reduction observed in OTFTs. Valence band and NEXAFS spectra show no evidence of new states in the bandgap. These findings demonstrate the potential of OTFTs as dosimeters for high dose-rates and clarify how radiation alters the molecular structure and electronic behavior of the device.