Sequential Growth of Organic Semiconductor-Based Heterojunction Bilayers for Ambipolar Transistors and Inverters

Abstract

This study evaluated ambipolar organic thin-film transistors (OTFTs) and complementary-like inverters using N,N-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C₁₃) and pentacene bilayers deposited sequentially on a polymer-grafted SiO₂ dielectric. As the underlying layers in semiconductor heterojunction bilayers (HJBs), PTCDI-C₁₃ crystallites with a nominal thickness of 1–4 monolayers (ML) were deposited and reorganized thermally. Finally, the crystal growth of pentacene was intermediated on the PTCDI-C₁₃ crystallites. Semiconductor HJBs with 40 nm thick pentacene crystallites clearly exhibited ambipolar charge-carrier transport, even when 1 ML-thick PTCDI-C₁₃ crystallites were placed beneath pentacene. The ambipolar OTFTs exhibited various hole (μ_h) and electron (μ_e) mobilities of 0.10–0.75 and 0.013–0.55 cm² V^–1 s^–1, respectively, depending on the π-conjugated structures of the semiconductors. The terrace-like crystal growth of pentacene could be intermediated on the smooth-layered crystallites of PTCDI-C₁₃. An optimized OTFT could produce balanced μ_h and μ_e values as high as 0.60 and 0.55 cm² V^–1 s^–1, respectively. In addition, complementary-like inverters using two ambipolar OTFTs yielded a high voltage gain of up to 80.