Microcrystallization of a Solution-Processable Organic Semiconductor in Capillaries for High-Performance Ambipolar Field-Effect Transistors

We report on the use of microcrystallization in capillaries to fabricate patterned crystalline microstructures of the low-bandgap ambipolar quinoidal quaterthiophene derivative (QQT(CN)4) from a chloroform solution. Aligned needle-shaped QQT(CN)4 crystals were formed in thin film microstructures using either open- or closed- capillaries made of polydimethylsiloxane (PDMS). Their charge transport properties were evaluated in a bottom-gate top-contact transistor configuration. Hole and electron mobilities were found to be as high as 0.17 and 0.083 cm² V^-1 s^-1, respectively, approaching the values previously obtained in individual QQT(CN)4 single crystal microneedles. It was possible to control the size of the needle crystals and the microline arrays by adjusting the structure of the PDMS mold and the concentration of QQT(CN)4 solution. These results demonstrate that the microcrystallization in capillaries technique can be used to simultaneously pattern organic needle single crystals and control the microcrystallization processes. Such a simple and versatile method should be promising for the future development of high-performance organic electronic devices.