For the first time, x-rays have been directly detected by a thick film (up to 20 µm) of conjugated polymers. The arrangement is significant because such a film can be coated over large areas and over free-form surfaces, making this sort of detector very versatile. The approach is also simpler than the more-usual reliance on fluorescence or luminescence.
Two different conjugated polymers, MEH-PPV and PFO, were tested; the substances were drop-cast in a solution onto a glass substrate coated with an indium tin oxide electrode and a hole-injecting polymer blend; the structure was capped with a 100 nm aluminum electrode film. When irradiated by a 50 kV x-ray tube with a molybdenum target, both polymers showed linear increases in photocurrent over a dose-rate range from 4 to 18 mGy/s (one Gy, or gray, is equal to an absorbed dose of 1 J/kg). The x-ray sensitivities of 240 and 480 nC/mGy/cm3 for MEH-PPV and PFO, respectively, were similar to that for silicon-based x-ray detectors. The large-area conjugated-polymer detector will be useful in medical, security, and scientific applications. Contact Paul Sellin at [email protected].