Solution-Processed Organic Field-Effect Transistors

Compare with inorganic transistors, OFETs has low mobility, poor air stable and it is relatively difficult to large area patterning. It is a difficult problem to improve the performances of OFETs. The electrode material and the nature of the interface between the dielectric and the semiconductor layer effect on the performances of the OFETs. Poly(methyl-methacrylate)(PMMA) have always been used as a dielectric layer, the surface properties of PMMA effect on the interface state of the semiconductor layer and the nature of the interface between the dielectric and the semiconductor layer. Therefore, in order to obtain high performance OFETs, these aspects of the device need to be systematic researched, analysis OFETs electron transfer mechanism, and to identify ways to improve the device performances. The OFETs of the paper was prepared by Sol-Gel, and we also discuss the effects of the different metal electrodes, dielectric with different treatment method on device performances. At the same time we also obtain a high-performance OFET by UV/Ozone treat PMMA.Among various types of polymer semiconductors, poly(3-hexylthiophene)(P3HT) due to its good film-forming properties, solubility in organic solvents, and hole transporting properties has been investigated for device applications. But the performances of P3HT-based OFETs are poor because P3HT is sensitive to atmosphere. So it is still very challenging to get high-performance P3HT-based OFETs in ambient conditions. Poly(methyl-methacrylate)(PMMA) has been used as dielectric layer to improve the performances of the P3HT-based OFETs due to its good film-forming and excellent dielectric properties. In this study, we prepared OFETs by Sol-Gel, which P3HT as the semiconductor layer, PMMA as a dielectric layer. In this paper, we discuss three aspects as follow:(1) Charge injection in regioregular poly-(3-hexythiophene) organic field-effect transistors with different metal electrodes.Here we report on regioregular poly-(3-hexythiophene)(P3HT) organic field-effect transistors (OFETs) with various metal electrodes:pristine Au, pristine Cr, and Cr/Au. Compared to the performance of OFETs using different electrodes, the OFETs with Au electrode have better mobility (μ=0.0090cm2/Vs) and larger current at the same source-drain voltage and gate voltage. The enhancement of the device performance with Au electrode can be attributed to a small contact resistance and a small barrier height to P3HT for hole carrier injection. (2) The effects of PMMA with different heat treatment temperature on the performances of OFETs.PMMA treatment process has an important influence on the performance of the OFETs. We prepare OFETs by Sol-Gel, which Au as electrodes. In this paper, we compared the performances of the OFETs with PMMA treated by different temperatures and discussed the changes of the performances of the OFETs with the PMMA treated by different temperatures. We obtained high performances OFET with the PMMA treated by different temperatures. Compared with different OFETs we found the OFET with PMMA treated by120℃had a larger mobility and larger on/off current ratio, but the devices have a large threshold voltage. The surface of the semiconductor of the OFET with PMMA treated by120℃showed a amorphous state, the amorphous state reduced the grain boundary of the semiconductor, thus facilitating the transfer of carriers and improved the mobility and on/off current ratio. The OFETs had a large off-current because of the larger leakage current. If we improve the performance of the dielectric of the OFETs, the leakage current will be reduced and the on/off current ratio will be improved.(3) High performance poly(3-hexylthiophene) thin-film transistors prepared by room temperature method.Poly(3-hexylthiophene)-based organic field-effect transistors (OFETs) utilizing poly(methyl methacrylate)(PMMA) as a dielectric layer were fabricated by using a solution process. UV/Ozone is a room temperature and simple method to treat organic layers. To improve the property of PMMA, UV/Ozone has been used as an auxiliary method after annealing. Recently, the effects of UV treatment of gate dielectric on the device performance in pentacene OFETs were reported. The device performance of the OFETs based on UV/Ozone-treated PMMA films demonstrated a relatively high μ value0=0.012cm2/Vs) and on/off current ratio (Ion/loff=1.2×103). The effects of UV/Ozone on the performance of OFETs were investigated. The results showed that UV/Ozone is a room temperature and simple method to treat organic layer and desirable for low-cost device fabrication. And the method is of great importance for flexible electronics using plastic film substrates.