High-mobility pentacene thin-film phototransistor with poly-4-vinylphenol gate dielectric

An organic thin-film transistor was fabricated with pentacene as the active material and poly(4-vinyl phenol) as the gate-dielectric material. Atomic force microscope image shows that the pentacene film grows in the polycrystalline structure of the poly-4-vinylphenol (PVP) dielectric layer with the surface root-mean square (RMS) roughness of 6.0 nm and average grain size of 800 nm. The pentacene thin-film transistor exhibited a saturation field-effect mobility of 1.64 cm²/V s, a threshold voltage of -18 V, a sub-threshold swing of 3.53 V/decade, on/off-current ratio of 7.1 × 10⁴ and interface trap density of 5.39 × 10¹² eV^-1 cm^-2. The higher mobility of pentacene on poly(4-vinyl phenol) layer is attributed to the larger grain size of the pentacene. The photoresponsive properties of the organic thin-film transistor were investigated under various illumination intensities. The photosensitivity was measured as 1.46 at an illumination intensity of 100 mW/cm² at the off state. This suggests that the pentacene thin-film transistor shows a phototransistor behavior.