Controlling the Threshold Voltage of Organic Thin-Film Transistors by Transition Metal Oxides

We demonstrate an effective, noble metal-free method to control the threshold voltages (VT) of organic thin-film transistors (OTFTs). Through covering an Al gate electrode with a high work function (WF) transition metal oxide (TMO) layer of WO₃ or MoO₃, VT is shifted in a positive direction from -2.15 V to -1.40 V or -0.89 V, respectively, with respect to that of OTFTs with a bare Al gate electrode. Together with a thin dielectric layer of cross-linked Cytop, the reduced magnitude of V_T allows for a low-voltage switching operation with a gate voltage as small as 2 V. The amount of V_T shift is shown to correlate well with the change in the WF of the gate electrode upon TMO deposition.