Electrical transport mechanism of single monolayer pentacene film employing field-effect characterization

• Single molecular layer FETs being built with recorded mobility of 0.3 cm2 V−1 s−1.
• 2D electrical transport mechanism in organic small molecular film.
• Untypical mobility-electric field relation was recorded and reasonably explained.

We employed a novel electrode-contact architecture to enable operation of single monolayer pentacene-based field-effect transistor with a high electrical performance, whose mobility reaches as high as 0.31 cm2 V−1 s−1, the highest among any pentacene-based monolayer devices ever reported. A temperature dependent charge transport was systematically carried out to elucidate the carrier transport mechanisms within even single layer of molecules. The carrier mobilities are found to exhibit a pure Arrhenius type at the high temperature regime (above 170 K), by contrast, a pronounced turning point has been observed when the measurement temperature is below 170 K, possible mechanisms were ascribed to the distribution attribute of trapped states among the grain boundary. Furthermore, an electric field dependent mobility characterization shows a unique non-Poole–Frenkel type behavior at room temperature, which shows much different from the case occurred in multiple-layer devices where the quantity of permitted percolation routes among different monolayers guarantees an mobility enhancement as an electric field increasing. But for the case of single monolayer, the electric field-induced potential reduction effect is competing with a drop of percolation path arising from the directional movement of carrier under a strong electric field. The depth understanding of carrier transport within one monolayer may be helpful for optimizing the design of OFETs for better device applications.

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