Solution-Processed Donor–Acceptor Poly(3-hexylthiophene):Phenyl-C₆₁-butyric Acid Methyl Ester Diodes for Low-Voltage α Particle Detection

Diodes fabricated using a blend of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester (6–80 μm thick) as an organic semiconductor component achieved consistent 4 MeV α particle detection. Current–voltage characteristics and current–time measurements were obtained under α irradiation and in its absence. Steady-state and transient (time-of-flight) photoconduction measurements were additionally performed. Low-bias (<20 V) α particle detection gain-efficiency products of order 10–2 were measured. The α 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 α 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 α particle, obtained by modeling, to the organic semiconductor layer thickness. Very high confidence α 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 cm2 V–1. This work demonstrates that solution-processed organic semiconductor diodes are viable for low-voltage α particle detection.