Dynamics of direct X-ray detection processes in high-Z Bi_2O_3 nanoparticles-loaded PFO polymer-based diodes

摘要

Semiconducting polymer based X-ray detectors doped with high-Z nanoparticles hold the promise to combine mechanical flexibility and large-area processing with a high X-ray stopping power and sensitivity. Currently, a lack of understanding of how nanoparticle doping impacts the detector dynamics impedes the optimization of such detectors. Here, we study direct X-ray radiation detectors based on the semiconducting polymer poly(9,9-dioctyfluorene) blended with Bismuth(III)oxide (Bi_2O_3) nanoparticles (NPs). Pure polymer diodes show a high mobility of 1.3 x 10~(-5) cm~2/V s, a low leakage current of 200nA/cm~2 at -80 V, and a high rectifying factor up to 3 x 10~5 that allow us to compare the X-ray response of a polymer detector in charge-injection conditions (forward bias) and in charge-collection conditions (reverse bias), together with the impact of NP-loading in the two operation regimes. When operated in reverse bias, the detectors reach the state of the art sensitivity of 24 μC/Gy cm~2, providing a fast photoresponse. In forward operation, a slower detection dynamics but improved sensitivity (up to 450 ±150 nC/Gy) due to conductive gain is observed. High-Z NP doping increases the X-ray absorption, but higher NP loadings lead to a strong reduction of charge-carrier injection and transport due to a strong impact on the semiconductor morphology. Finally, the time response of optimized detectors showed a cut-off frequency up to 200 Hz. Taking advantage of such a fast dynamic response, we demonstrate an X-ray based velocity tracking system.