Field-Effect Charge Transport in Doped Polymer Semiconductor-Insulator Alternating Bulk Junctions with Ultrathin Transport Layers.

Conjugated-polymer field-effect transistors are attractive for flexible electronics. However, relatively high chemical doping (oxidation) concentration of p-type polymer semiconductors is usually not compatible with good transistor performance, due to poor switching-off capability and short-channel performance. Here, we propose a combined simulation and experimental investigation on charge transport in a semiconductor-insulator alternating bulk junction composed of repeating semiconductor and insulator regions, which shows better transistor performance at higher doping levels, as compared with traditional planar transistors. Moreover, the doped semiconductor transport layers in the junction should be less than 2 nm thick to ensure sufficient pinch-off capability. Using some semiconductors including poly(3-hexylthiophene), we utilize a fast solvent evaporation approach to obtain semiconductor-insulator alternating bulk junctions with ultrathin (thickness < 2 nm) semiconductor crystallites and with vertical gradients of both morphology and electronic properties. Doping with a concentration of up to 1019 cm-3 simultaneously induces the improvement of field-effect mobility, on/off ratio, and subthreshold swing, which leads to long-term (>1 year) stability, without lowering the short-channel performance. Moreover, these heterojunctions are optically transparent, nearly colorless, and flexible, thus could be exploited for wide electronic and photonic applications.