Modulating contact properties by molecular layers in organic thin-film transistors

Abstract

Advanced organic devices and circuits demand both ultrahigh charge carrier mobilities and ultralow-resistance contacts. However, due to a larger access resistance in staggered organic thin-film transistors (OTFTs), the achievement of ultralow contact resistance () is still a challenge. The modulation of contact resistance by molecular layers near the interface has been rarely reported. Here, we demonstrate that few-layer organic single crystals are grown on hafnium oxide (HfO₂) by solution-shearing epitaxy. We utilize these organic crystals to fabricate bottom-gate staggered OTFTs with different contact processes. The results show that the contact properties of OTFTs are obviously modulated by crystal layers. The tri-layer (3L) evaporated-Au C₁₀-DNTT OTFTs exhibit optimal electrical performance, including ultralow of 5.6 Ω ∙ cm, recorded transfer length of 0.4 μm, field-effect mobility over 14 , threshold voltage lower than 0.3 V, and long-term air stability over 8 months. The main cause is that the metal atoms can penetrate into the charge transport layer, with damage-free, in 3L evaporated-Au OTFTs; nevertheless, it cannot be realized in other cases. Due to layer stacking of conjugated molecules and polymers, our strategy can efficiently modulate the contact resistance to aid the development of high-performance organic devices and circuits.