Enhancing Contact Properties in Organic Thin-Film Transistors by Incorporating Organic Solid-Solution Semiconductor Buffer Layers

The interface between organic semiconductors and metal electrodes remains a major challenge in organic thin-film transistors (OTFTs), which limits the transit frequency of OTFTs in logic circuits and leads to inaccurate assessment of charge transport. In this work, we propose a novel strategy to enhance interfacial contact by employing organic solid-solution films (SSFs) as buffer layers between electrodes and semiconductors. Finite organic solid-solution semiconductors, (P5)<i>_<i>x</i></i>(C8-BTBT)_1-<i>x</i>, were successfully fabricated via coevaporation of P5 and C8-BTBT molecules. Substitutional solid solutions were formed for <i>x</i> < 0.5, while phase separation was observed for <i>x</i> ≥ 0.5. OTFTs incorporating SSFs as interfacial buffer layers effectively eliminate the nonlinear behavior of output characteristics, exhibiting a substantial reduction in contact resistance and achieving a high carrier mobility of up to 4.6 cm²/(V s). This improvement is attributed to interfacial energy level alignment and lattice matching, which significantly lower the injection barrier and reduce interfacial structural defects. Our results provide a promising approach for optimizing semiconductor/metal contacts to improve the overall performance of organic transistors.