Performance improvement mechanisms of organic thin-film transistors using MoOx-doped pentacene as channel layer

Organic thin-film transistors (OTFTs) with various MoOx-doped pentacene channel layers were fabricated and investigated. Compared the OTFTs with the 0.50 mol% MoOx-doped pentacene to the conventional OTFTs without MoOx dopant, the maximum output current was increased from −11.6 to −37.9 μA, the effective field-effect mobility was enhanced from 0.71 to 1.60 cm2/V-s, the threshold voltage was reduced from −21.2 to −14.8 V, and the on/off current ratio slightly decreased from 3.6 × 106 to 1.2 × 106. The performance improvement was attributed to the highest occupied molecular orbital (HOMO) of the MoOx-doped pentacene gradually approached to the Au work function with increasing the doping percentage of MoOx, which led to reduce the contact resistance and to enhance the p-type characteristics of the MoOx-doped OTFTs by increasing the hole density and enhancing the hole-injection efficiency. However, the output current and the field-effect mobility decreased with an increase of the MoOx doping percentage, if the doping mole percentage of MoOx was higher than 0.50%. This behavior was attributed to the Fermi level pinning effect, gradual increase of hole concentration and significant degradation of crystallinity.

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► Various MoOx-doped pentacene channel layers were used in the organic thin-film transistors.
► OTFTs with 0.5% MoOx-doped pentacene channel layer revealed the high current of 37.9 μA and high mobility of 1.6 cm2/V-s.
► Various MoOx-doped pentacene layers were analyzed by UPS, XRD and XPS to study physical mechanisms.
► The percentage of various Mo oxidation states in the 0.5% MoOx-doped pentacene was estimated using XPS.