Studies On Preparation And Properties Of Organic Thin Film Transistors Based On Polythiophene Composites

Organic thin film transistors based on blends of semiconducting polymers andinsulating polymers have been concerned by researcher from the very beginning,for not only inheriting the solution processability of organic semiconductors, butalso saving materials cost and improving environmental stability. Especiallyimparting new characteristics of the active layer, such as good mechanicalproperties, low-temperature plasticity and photosensitivity, which provide apotential development for preparing flexible organic electronic devices with stableperformance and low consumption.In this thesis, organic thin film transistors based on polythiophene compositeshave been studied, the main contents include:（1） A crystalline-crystalline blending system containing poly（3-hexylthiophene）and polycaprolactone was used for organic thin-film transistors with highperformance. The electric measurements reveal that the field-effect performancesof blend films, such as mobility, Ion/off current ratio and threshold voltage,decrease slowly with P3HT content reducing. However, the devices still haverelatively good performance as P3HT content was as low as40wt%. Accordingto the AFM studies, vertical phase separation occurs in the blend films, and aconnective semiconducting layer can be observed at the interface betweeninsulating layer and active layer, which is beneficial to transport of charge carriers.（2） A melt processing method based on a blend of poly（3-hexylthiophene）（P3HT） and a selected insulating polymer with good melt-processability,poly（ε-caprolactone）（PCL）, has been demonstrated for fabricating organicthin-film transistors. In the blend, P3HT component presents as a nanofibrillarnetwork embedded in PCL matrix and thus provides excellent charge transportproperty at P3HT/PCL ratio of1/5. The low P3HT content allows the blend beingprocessed at a low temperature about60oC. The field-effect transistor fabricated bymelt method show saturated field-effect mobility of1.1×10^-2cm²V^-1s^-1andIon/Ioff ratios about10⁴. Furthermore, The blend display outstanding mechanicproperty with elongations at break exceeding300%.（3） A blend of organic semiconductors and photocrosslinkable insulating polymers was photolithographically patterned to yield organic thin-film transistors（OTFTs）. The semiconducting polymer of the blend, poly（3-hexylthiophene）, waspresent as a nanofibrillar network and yielded excellent electronic properties. Theinsulating polymer matrix, poly（vinyl cinnamate）, provided the photosensitivityrequired for photopatterning. The photopatterned TFT devices showed large on/offratios （>10⁵） and high mobilities (0.015cm²V^-1s^-1) comparable to those of devicespatterned by conventional means using the same semiconducting materials.