High-performance organic thin-film transistors with metal oxide/metal bilayer electrode

We demonstrate bilayer source-drain $\left(S\text{-}D\right)$ electrodes for organic thin film transistors (OTFT). The bilayer consists of a transition metal oxide ($\mathrm{Mo}{\mathrm{O}}_3,\mathrm{W}{\mathrm{O}}_3$ , or ${\mathrm{V}}_2{\mathrm{O}}_5$ ) layer and a metal layer. The metal oxide layer, directly contacting the organic semiconducting layer, serves as the charge-injection layer. The overcoated metal layer is responsible for the conduction of charge carriers. We found that the metal oxide layer coupled between pentacene and metal layers played an important role in improving the field-effect transistor characteristics of OTFTs. Devices with the bilayer $S\text{-}D$ electrodes showed enhanced hole-injection compared to those with only metal electrode. High field-effect mobility of $0.4{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ and on/off current ratios of ${10}^4$ were obtained in the pentacene based TFTs using the bilayer $S\text{-}D$ electrodes at a gate bias of $-40\mathrm{V}$ . The improvement is attributed to the reduction in the contact barrier and the prevention of metal diffusion into the organic layer and/or unfavorable chemical reaction between the organic layer and the metal electrode.