π-Conjugated organic-based devices with different layered structures produced by the neutral cluster beam deposition method and operating conduction mechanism

The authors report on the systematic characterization of structural effects of organic complementary inverters based on two -conjugated organic molecules, pentacene and copper hexadecafluorophthalocyanine (F₁₆CuPc). Three classes of inverters with different layered structures in top-contact configuration were produced using the neutral cluster beam deposition method. Their voltage transfer characteristics, gain curves and hysteresis behaviour were characterized with respect to their thickness. Class I inverters, with generic structures of single-layered, p-and n-type (200/180) transistors, exhibited high gains of 12.8 ± 1.0 with sharp inversions. Their two constituent transistors, with hole and electron mobilities of 0.38 cm ² V^-1 s^-1 and 7.0 × 10^-3 cm² V^-1 s^-1, respectively, showed well-coupled carrier conduction during operation. The behaviour of class II and III inverters, with layered heterojunction structures, was independent of upper-layer thickness and did not show hysteresis. The better performances of class II inverters, which showed high gains of 14.4 ± 1.1, were rationalized partly in terms of decreased mobility differences between their constituent transistors. Heterojunction geometries can be applied to obtain high-performance, fast-switching inverters by avoiding direct exposure of the air-sensitive transistors to ambient conditions. The inverters' general operating conduction mechanism is also discussed.