Paul Craig Brookes

Morphology control via dual solvent crystallization for high-mobility functionalized pentacene-blend thin film transistors

We present an approach to improving the performance of solution processed organic semiconductor transistors based on a dual solvent system. We here apply this to a blend containing the π-conjugated small molecule 6,13 bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) and polystyrene, which acts as an inert binder. Using a semiconductor-binder solution of two solvents, where the main solvent is a better solvent of the small molecule and second solvent is a better solvent of the polymer, crystal morphologies can be altered and transistor mobilities increased by almost an order of magnitude. In this way, air-ambient and solution-processed transistors with linear and saturation mobilities higher than 1 cm2 V−1s−1 have been fabricated. We discuss how the solubility properties of the formulation components can be used to identify solvent candidates that promote an efficient self-assembly of the small molecule.

Development of TFT device stack for integration of organic semiconductors into flexible displays

To enable the integration of organic transistors into flexible displays we have developed passive materials for a robust, layer-to-layer compatible device stack to be manufactured using a variety of industrially applicable coating and printing processes. The solution processable materials for the OSC protection and the passivation material are designed for good interlayer adhesion and OTFT stability. The 365 nm UV-curable protection layers for the OSC are compatible with fabrication processes commonly used in the display industry, e.g., sputtering of metals. Fabrication of ink-jet printed devices is demonstrated with usage of a passive material suitable for further pixel integration. The bias stress and ambient stability was shown for the integrated stacks of transistors with the carrier mobility greater than that of amorphous silicon. We further demonstrate the development of formulations, suitable for high throughput roll-to-roll processing of soluble small molecule semiconductors allowing a high degree of structural order in the final solid film. Transistor mobility <2 cm2/V·s is achieved with a range of viscosity values compatible with flexographic printing. Fine pattern of OSC is demonstrated with flexographic printing by adjusting the viscosity of the formulation. Uniform layers are achieved with coating and printing techniques and uniformity values are sufficient for display application.