Mechanistic Analysis of Embedded Copper Oxide in Organic Thin-Film Transistors with Controllable Threshold Voltage

The modulation of threshold voltage (V _TH) of organic thin-film transistors (OTFTs) was investigated by embedding a thin CuO layer between the two semiconductor layers. The results showed that the V _TH of OTFTs with a CuO layer can be effectively tuned by controlling the positive gate-to-source voltage (V _GS0) under stress of gate-to-source voltages. The V _TH shifts from -3.67 to -0.82 V when the positive V _GS0 varies from 30 to 50 V. This can be explained by the mechanism of trapping electrons at the interface between the CuO charge-separation layer and the active layer. To confirm the role of the CuO layer acting as the charge-separation source, two organic thin-film diodes, indium-tin oxide(ITO)/tris (8-quinolinolato) aluminum(III) (Alq₃)/pentacene/Al (inverted-stack diode) and ITO/Alq₃/CuO/pentacene/Al (inverted-stack diode with a CuO layer), were fabricated and their diode current characteristics were measured. For the second device, a large current flow was observed at positive bias on the ITO electrodes, which is ascribed to the internal bipolar charge separation within the added CuO zone.