High-Z nanoparticles for enhanced sensitivity in semiconducting polymer X-ray detectors

Semiconducting polymers have previously been used as the transduction material in X-ray dosimeters, but these devices have a rather low detection sensitivity because of the low X-ray attenuation efficiency of the organic active layer. Here, we demonstrate a way to overcome this limitation through the introduction of high density nanoparticles having a high atomic number (Z) to increase the X-ray attenuation. Specifically, bismuth oxide (Bi2O3) nanoparticles (Z = 83 for Bi) are added to a poly(triarylamine) (PTAA) semiconducting polymer in the active layer of an X-ray detector. Scanning electron microscopy (SEM) reveals that the Bi2O3 nanoparticles are reasonably distributed in the PTAA active layer. The reverse bias d.c. current-voltage characteristics for PTAA-Bi2O3 diodes (with indium tin oxide (ITO) and Al contacts) have similar leakage currents to ITO/PTAA/Al diodes. Upon irradiation with 17.5 keV X-ray beams, a PTAA device containing 60 wt.% Bi2O3 nanoparticles demonstrates a sensitivity increase of approximately 2.5 times compared to the plain PTAA sensor. These results indicate that the addition of high-Z Published in Nanotechnology 23 (2012) 235502 2 nanoparticles improves the performance of the dosimeters by increasing the X-ray stopping power of the active volume of the diode. Because the Bi2O3 has a high density, it can be used very efficiently, achieving a high weight fraction with a low volume fraction of nanoparticles. The mechanical flexibility of the polymer is not sacrificed when the inorganic nanoparticles are incorporated. PACS code: 81, 85 and 89