Hole transport in amorphous-crystalline-mixed and amorphous pentacene thin-film transistors

Abstract
We report on the hole transport behavior in amorphous-crystalline-mixed and amorphous pentacene thin-film transistors. Five organic thin-film transistors (OTFTs) were fabricated by evaporating the pentacene films at rates of 1, 3, 5, and 7 Å/s at 25 °C (RT), and 7 Å/s at 60 °C. The field-effect mobility increased with the deposition rate even though the crystalline quality of the pentacene film degraded from an amorphous-crystalline-mixed phase to an amorphous phase. With our optimum deposition rate of 5 Å/s at RT, we obtained a saturation current (I D- SAT ) of about 4 μA at a gate bias of −40 V, the field-effect mobility of 0.1 cm2/V s, and the on/off current ratio of 10 5 . For the OTFT prepared with a deposition rate of 7 Å/s at 60 °C, an amorphous pentacene channel layer with a high mobility of ∼0.3 cm2/V s and the on/off current ratio of 10 4 were observed.