High-performance poly(3-hexylthiophene) top-gate transistors incorporating TiO2 nanocomposite dielectrics

This paper describes the fabrication of top-gate P3HT organic field effect transistors (OFETs) incorporating polymer/TiO2 nanocomposite bilayer dielectrics. The TiO2 nanocomposite comprised PVP, the cross-linking agent PMF, and TiO2 nanoparticles (NPs), which possessed rod-like anatase structures and were solution-processable using polar solvents; thus, the composite dielectric solutions were easy to be prepared for the use in top-gate OFET devices without damaging and dissolution of the underlying P3HT film. SEM and AFM images revealed the high uniformity of the nanocomposite films. To determine the effects of the composite dielectrics with/without TiO2 on the performance of the OFET devices, we inserted a buffer layer of PMMA between the semiconductor layer and the gate dielectric to maintain a constant semiconductor–dielectric interface. The device incorporating the PMMA/TiO2 nanocomposite bilayer gate dielectric operated effectively at supply voltages within 20 V, with a good mobility (μ) of 1.5 × 10−2 cm2 V−1 s−1, which was three times greater than that of the devices featuring the PMMA/PVP/PMF dielectric; the on/off ratio of nanocomposite device (8.6 × 106) was significantly better than that of the PVP/PMF device (1.5 × 105). The PMMA/TiO2 nanocomposite was also performed acceptably at supply voltages of less than 10 V. The performance of the OFET incorporating a single dielectric layer of the TiO2 nanocomposite (μ = 0.001 cm2 V−1 s−1; on/off ratio = 5.7 × 102) was inferior to those of the bilayer gate dielectric devices.