Stability of X-Ray Detectors Based on Organic Photovoltaic Devices

We study the radiation hardness of a prototype X-ray detector consisting of a thin-film organic photovoltaic (OPV) device based on a blend of the conjugated polymer poly(3-hexylthiophene) (P3HT) with the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM), coupled with a sheet of the inorganic scintillator Gd₂O₂S:Tb. We show that as the device is exposed to a flux of 15-MV X-rays, the recorded photocurrent undergoes a near exponential decay described by two decay constants of 1.6×10^-4 and 1.8×10^-3 Gy^-1. In order to understand the degradation mechanisms of the device, we expose the constituent parts to a significant dose (~4.2 kGy) of 15-MV X-rays and record changes in the photoluminescence and absorption spectra of the P3HT, and also explore the current-voltage characteristics and external quantum efficiency of the OPVs. We use our results to comment on the induced degradation mechanisms resulting from the exposure to X-rays.