High-performance organic thin film transistors based on inkjet-printed polymer/TIPS pentacene blends

The blending of crystalline organic semiconductor, 6,13- bis(triisopropylsilylethynyl)-pentacene (TIPS pentacene) with amorphous polymers exhibits not only excellent solution processibility but also superior performance characteristics in organic thin film transistors (OTFTs). To understand the inkjet printing behavior of polymer/TIPS pentacene blends, we synthesized triarylamine-based polymers with various polarities, which were obtained by changing the fluorine content in the polymer structure. The variation of segregation strength of the polymer domains in the blends can be induced depending on the different polarities of the polymers, which can ultimately determine the shape and orientation of the TIPS pentacene crystals in OTFT films. This relationship was explained by the Flory-Huggins phase separation theory according to the measured TFT performance. Polarized optical microscopy, 3D surface profile, and X-ray diffraction (XRD) were used to investigate the crystal orientation, surface morphology, and crystallinity of the polymer/TIPS pentacene thin films. The experimental results suggest that the phase separation behavior between the polymer and TIPS pentacene plays a significant role in the formation of crystal structure of TIPS pentacene in the film. The moderate segregation of the polymers from the TIPS pentacene crystal domains effectively derives the desirable stripe-shaped crystals with the proper orientation and enhanced surface morphology. The resultant inkjet-printed films from the triarlyamine-based polymers with TIPS pentacene showed excellent mobility of 0.14-0.19 cm² V^-1 s^-1, which are among the highest values obtained by inkjet printing reported to date.