Co-reporter:Kyeiwaa Asare–Yeboah, Sheng Bi, Zhengran He, Dawen Li
Organic Electronics 2016 Volume 32() pp:195-199
Publication Date(Web):May 2016
DOI:10.1016/j.orgel.2016.02.028
•Well-aligned crystals and enhanced areal coverage were achieved via temperature gradient.•Incorporation of polymer eliminates thermal cracks, improving charge transport.•The crystal growth technique is fully compatible with flexible substrate.6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) from simple drop casting typically forms crystals with random orientation and poor areal coverage, which leads to device-to-device performance variation of organic thin film transistors (OTFTs). Previously, a temperature gradient technique was developed to address these problems. However, this approach simultaneously introduced thermal cracks due to the thermally induced stress during crystallization. These thermal cracks accounted for a reduction of charge transport, thereby impacting the device performance of TIPS pentacene based OTFTs. In this work, an insulating polymer, poly(α-methyl styrene) (PαMS) was blended with TIPS pentacene to relieve the thermal stress and effectively prevent the generation of thermal cracks. The results demonstrate that the incorporation of PαMS polymer combined with the temperature gradient technique improves both the hole mobility and performance consistency of TIPS pentacene based OTFTs.
Co-reporter:Zhengran He, Nereo Lopez, Xiaoliu Chi, Dawen Li
Organic Electronics 2015 Volume 22() pp:191-196
Publication Date(Web):July 2015
DOI:10.1016/j.orgel.2015.03.050
Co-reporter:Sheng Bi;Che-Nan Sun;Thomas A. Zawodzinski Jr.;Fei Ren;Jong Kahk Keum;Suk-Kyun Ahn;Jihua Chen
Journal of Polymer Science Part B: Polymer Physics 2015 Volume 53( Issue 20) pp:1450-1457
Publication Date(Web):
DOI:10.1002/polb.23793
ABSTRACT
Solid polymer electrolytes based on lithium bis(trifluoromethanesulfonyl) imide and polymer matrix were extensively studied in the past due to their excellent potential in a broad range of energy related applications. Poly(vinylidene fluoride) (PVDF) and polyethylene oxide (PEO) are among the most examined polymer candidates as solid polymer electrolyte matrix. In this work, we study the effect of reciprocated suppression of polymer crystallization in PVDF/PEO binary matrix on ion transport and mechanical properties of the resultant solid polymer electrolytes. With electron and X-ray diffractions as well as energy filtered transmission electron microscopy, we identify and examine the appropriate blending composition that is responsible for the diminishment of both PVDF and PEO crystallites. A three-fold conductivity enhancement is achieved along with a highly tunable elastic modulus ranging from 20 to 200 MPa, which is expected to contribute toward future designs of solid polymer electrolytes with high room-temperature ion conductivities and mechanical flexibility. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1450–1457
Co-reporter:Zhengran He, Jihua Chen, Jong Kahk Keum, Greg Szulczewski, Dawen Li
Organic Electronics 2014 Volume 15(Issue 1) pp:150-155
Publication Date(Web):January 2014
DOI:10.1016/j.orgel.2013.11.004
•The addition of small molecules improved TP crystal orientation and areal coverage.•The improvement depends on the length of alkyl side chains of small molecule additives.•OTFTs based on TP/small molecule blend demonstrated a significant enhancement in performance.This work demonstrates an effective approach to improve both charge transport and performance consistency in solution-processed organic thin-film transistors (OTFTs) by blending 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene, or TP) with a series of small-molecule additives: 4-butylbenzoic acid (BBA), 4-hexylbenzoic acid (HBA), and 4-octylbenzoic acid (OBA). These three small molecules share a benzoic acid moiety, but have different length of hydrophobic tails. The self-assembled interfacial layer of small molecules on the gate oxide surface leads to uniform deposition of TP crystal seeds and facilitates TP to grow along the tilted orientation of substrate, which results in a film of enhanced crystal orientation and areal coverage. OTFTs based on TP/small molecule blends demonstrate greatly improved average hole mobility and performance consistency, which correlates with the length of hydrophobic tail of the small-molecule additives.
Co-reporter:Zhengran He, Jihua Chen, Zhenzhong Sun, Greg Szulczewski, Dawen Li
Organic Electronics 2012 Volume 13(Issue 10) pp:1819-1826
Publication Date(Web):October 2012
DOI:10.1016/j.orgel.2012.05.044
6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) is a promising active channel material of organic thin-film transistors (OTFTs) due to its solubility, stability, and high mobility. However, the growth of TIPS pentacene crystals is intrinsically anisotropic and thus leads to significant variation in the performance of OTFTs. In this paper, air flow is utilized to effectively improve the TIPS pentacene crystal orientation and enhance performance consistency in OTFTs, and the resulted films are examined with optical microscopy, X-ray diffraction, and thin-film transistor measurements. Under air-flow navigation (AFN), TIPS pentacene drop-cast from toluene solution has been observed to form thin films with improved crystal orientation and increased areal coverage on substrates, which subsequently lead to a fourfold increase of average hole mobility and one order of magnitude enhancement in performance consistency defined by the ratio of average mobility to the standard deviation of the field-effect mobilities.Graphical abstractHighlights► Air flow effectively improves TIPS pentacene crystal alignment and enhances OTFT performance consistency. ► Under air-flow navigation, TIPS pentacene films show improved crystal orientation and areal coverage. ► Demonstrating a fourfold increase of average mobility and one order of magnitude enhancement in performance consistency.
Co-reporter:Zhengran He;Kai Xiao;William Durant;Dale K. Hensley;John E. Anthony;Kunlun Hong;S. Michael Kilbey II;Jihua Chen
Advanced Functional Materials 2011 Volume 21( Issue 19) pp:3617-3623
Publication Date(Web):
DOI:10.1002/adfm.201002656
Abstract
In this study, inorganic silica nanoparticles are 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 times reduction in the ratio of measured mobility standard deviation (μStdev) to average mobility (μAvg). 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. The experimental results suggest that the SiO2 nanoparticles mostly aggregate at TIPS pentacene grain boundaries, and 10% nanoparticle concentration effectively reduces the undesirable crystal misorientation without considerably compromising TIPS pentacene crystallinity.
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