Gradual Controlling the Work Function of Metal Electrodes by Solution-Processed Mixed Interlayers for Ambipolar Polymer Field-Effect Transistors and Circuits

In this paper, a technique using mixed transition‐metal oxides as contact interlayers to modulate both the electron‐ and hole‐injections in ambipolar organic field‐effect transistors (OFETs) is presented. The cesium carbonate (Cs2CO3) and vanadium pentoixide (V2O5) are found to greatly and independently improve the charge injection properties for electrons and holes in the ambipolar OFETs using organic semiconductor of diketopyrrolopyrrolethieno[3,2‐b]thiophene copolymer (DPPT‐TT) and contact electrodes of molybdenum (Mo). When Cs2CO3 and V2O5 are blended at various mixing ratios, they are observed to very finely and constantly regulate the Mo's work function from −4.2 eV to −4.8 eV, leading to high electron‐ and hole‐mobilities as high as 2.6 and 2.98 cm2 V−1 s−1, respectively. The most remarkable finding is that the device characteristics and device performance can be gradually controlled by adjusting the composition of mixed‐oxide interlayers, which is highly desired for such applications as complementary circuitry that requires well matched n‐channel and p‐channel device operations. Therefore, such simple interface engineering in conjunction with utilization of ambipolar semiconductors can truly enable the promising low‐cost and soft organic electronics for extensive applications. A gradual control of the metal electrode's work function (Φ) by incorporating solution‐processed mixed contact interlayer of transition metal salts (Cs2CO3 and V2O5). Low‐cost Mo electrode with Φ = 4.5 eV is finely modulated between 4.2 eV and 4.8 eV by controlling mixed concentration, which are used as common source/drain electrodes in high‐mobility ambipolar polymer semiconductor OFETs and complementary‐like inverter circuit.