Solution-Processed Donor-Acceptor Poly(3-Hexylthiophene):Phenyl-C-61-Butyric Acid Methyl Ester Diodes For Low-Voltage Alpha Particle Detection

Diodes fabricated using a blend of poly(3-hexylthiophene) and phenyl-C-61-butyric acid methyl ester (6-80 mu m thick) as an organic semiconductor component achieved consistent 4 MeV alpha particle detection. Current-voltage characteristics and current- time measurements were obtained under alpha irradiation and in its absence. Steady-state and transient (time-of-flight) photoconduction measurements were additionally performed. Low-bias (<20 V) alpha particle detection gain-efficiency products of order 10(-2) were measured. The alpha particle detection was achieved reproducibly, reversibly, and repeatably in different devices of varying organic semiconductor layer thicknesses using both the steady-state and time-dependent (dynamic) diode responses. Conductive gain, due to trapped electrons, increased the alpha particle gain-efficiency product in both forward and reverse bias conditions as well as increasing steady-state photoconduction. The device thickness was optimized to maximize the gain-efficiency product by matching the penetration depth of the alpha particle, obtained by modeling, to the organic semiconductor layer thickness. Very high confidence alpha particle detection was achieved (with signal-to-noise ratios exceeding 20) under optimized device dimensions and drive conditions. Hecht function fitting of the gain-efficiency product versus electric field data returns mobility-lifetime products of order 10(-6) -10(-7) cm(2 )V(-1). This work demonstrates that solution-processed organic semiconductor diodes are viable for low-voltage alpha particle detection.