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

[Image: see text] 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) (Alq(3))/pentacene/Al (inverted-stack diode) and ITO/Alq(3)/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.