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

This study evaluated ambipolar organic thin-film transistors (OTFTs) and complementary-like inverters using N, N -ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C 13 ) and pentacene bilayers deposited sequentially on a polymer-grafted SiO 2 dielectric. As the underlying layers in semiconductor heterojunction bilayers (HJBs), PTCDI-C 13 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-C 13 crystallites. Semiconductor HJBs with 40 nm thick pentacene crystallites clearly exhibited ambipolar charge-carrier transport, even when 1 ML- thick PTCDI-C 13 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 cm 2 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-C 13 . An optimized OTFT could produce balanced μ h and μ e values as high as 0.60 and 0.55 cm 2 V –1 s –1, respectively. In addition, complementary-like inverters using two ambipolar OTFTs yielded a high voltage gain of up to 80.