Enhanced Performance Consistency in Nanoparticle/TIPS Pentacene-Based Organic Thin Film Transistors

Zhengran He,1 Kai Xiao,2William Durant,1 Dale K. Hensley,2 John E. Anthony,3 Kunlun Hong,2 S. Michael Kilbey II,2,4 and Jihua Chen*,2 Dawen Li*,1

1-Department of Electrical and Computer Engineering, Center for Materials for Information Technology, University of Alabama, Tuscaloosa, AL 35487 (USA)
2-Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (USA)
3-Department of Chemistry, University of Kentucky, Lexington, KY 40506 (USA)
4-Department of Chemistry, University of Tennessee, Knoxville, TN 37996 (USA)

In this study, we have shown that inorganic silica nanoparticles can be used to manipulate the morphology of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS pentacene) thin films and the performance of solution-processed organic thin-film transistors (OTFTs). This approach is taken to control crystal anisotropy, which is the origin of poor consistency in TIPS pentacene based OTFT devices. Thin film active layers are produced by drop-casting mixtures of SiO2 nanoparticles and TIPS pentacene. The resultant drop-cast films yield improved morphological uniformity at ∼10% SiO2 loading, which also leads to a 3-fold increase in average mobility and nearly 4-fold reduction in the ratio of measured mobility standard deviation to average mobility. Grazing-incidence X-ray diffraction, scanning and transmission electron microscopy as well as polarized optical microscopy are used to investigate the nanoparticle-mediated TIPS pentacene crystallization.

Compared to OTFTs made from neat TIPS pentacene, the OTFTs based on SiO2 nanoparticles/TIPS pentacene exhibit enhanced performance consistency. At 10% SiO2 concentration, the measured hole mobility is 0.13 ± 0.04 cm2 V−1 s−1 while the corresponding OTFTs made from neat TIPS pentacene have a mobility of 0.04 ± 0.04 cm2 V−1 s−1. TEM images reveal that the edges of TIPS pentacene crystals with 10% SiO2 are significantly darker and about 8 times wider than that of pure TIPS pentacene films, which is likely caused by nanoparticle aggregation at TIPS pentacene grain boundaries. Both polarized optical microscopy images and X-ray diffraction results demonstrate that, with 10% SiO2 nanoparticles, improved crystal orientation is achieved while maintaining relatively high level of TIPS pen¬tacene crystallinity. Overall, this work demonstrates that nanoparticle addition provides a novel means to mediate the crystallization of solution-processed small-molecule organic semiconductors and may be used to effectively reduce the performance variation of solution-based organic thin-film transistors.

This work was published in Advanced Functional Materials DOI: 10.1002/adfm.201002656. This research was supported by the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U. S. Department of Energy.