The inverted-coplanar, or bottom-gate bottom-contact (BGBC), architecture is well-suited for practical organic thin-film transistors (OTFTs). However, its performance is often limited by inefficient carrier injection at the semiconductor/electrode/dielectric ternary interface. Here, we demonstrate that interfacial carrier accumulation plays a crucial role in enabling efficient injection at these ternary interfaces. We fabricate prototypical single-crystal BGBC OTFTs using alkylated organic semiconductors and systematically tune the source/drain electrode work functions via self-assembled monolayer modifications. A substantial decrease in current is observed as the electrode work function decreases, even in sharp-switching OTFTs with nearly trap-free transport interfaces, achieved using CYTOP as the gate dielectric. Contact resistance for low-work-function electrodes is found to be several orders of magnitude higher than that for high-work-function electrodes, confirming that the current reduction originates from injection inefficiency. Moreover, current decreases drastically when a gate dielectric with a higher trap density is used, indicating that carrier traps at the ternary interface further hinder carrier injection. These results highlight the necessity of maintaining sufficient carrier accumulation while minimizing trapping at the ternary interface to achieve efficient carrier injection in BGBC OTFTs.

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• Carrier dynamics
• Field-effect transistors
• Organic transistors
• Surface & interfacial phenomena
• Organic semiconductors
• Single crystal materials
• Solid-solid interfaces
• Resistivity measurements