Tuning charge transport in solution-sheared organic semiconductors using lattice strain
TL;DR: A solution-processing technique in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules should aid the development of high-performance, low-cost organic semiconducting devices.
Abstract: A solution-processing method known as solution shearing is used to introduce lattice strain to organic semiconductors, thus improving charge carrier mobility. Solution-processed organic semiconductors show great promise for application in cheap and flexible electronic devices, but generally suffer from greatly reduced electronic performance — most notably charge-carrier mobilities — compared with their inorganic counterparts. Borrowing a trick from the inorganic semiconductor community, Giri et al. show how the introduction of strain into an organic semiconductor, through a simple solution-processing technique, modifies the molecular packing within the material and hence its electronic performance. For one material studied, the preparation of a strained structure is shown to more than double the charge-carrier mobility. Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications1,2,3,4,5. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice6. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π–π stacking distance) greatly influences electron orbital overlap and therefore mobility7. Using our method to incrementally introduce lattice strain, we alter the π–π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33 A to 3.08 A. We believe that 3.08 A is the shortest π–π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π–π distance of 3.04 A has been achieved through intramolecular bonding8,9,10). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from 0.8 cm2 V−1 s−1 for unstrained films to a high mobility of 4.6 cm2 V−1 s−1 for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.
Figures (4)
Fig. 2: Molecular packing structure of TIPSE-pentacene prepared under different conditions. (A) Evaporated thin film. (B) Solution sheared film at 8 mm/s. (C) Solution sheared film at 8 mm/s, viewed along the b axis. The sphere represents the TIPSE group. The yellow and green colors correspond to the front and back of the molecule, respectively. The blue arrow in (c) represents the high charge transport direction, which is also the direction of shearing. 
Table 1: TIPSE-pentacene unit cell parameters and the corresponding TFT performance (average mobility, on/off ratio and threshold voltage) as a function of different shearing speeds. 
Fig. 1: (A) Schematic diagram of solution shearing method. (B) – (F) Cross polarized optical micrographs of solution sheared TIPSE-pentacene thin films, formed with shearing speed 0.4mm/s, 1.6mm/s, 2.8mm/s, 4mm/s and 8mm/s, respectively (scale bar is 200μm). Dark regions of the images are due to crystallites oriented along the polarization direction of the light. In all cases the white arrow represents the shearing direction. 
Fig. 3: (A) Charge carrier mobilities (left axis) and d-spacing (right axis) of TIPSE-pentacene thin films sheared at different speeds. The error bars show the standard error of the mean. (B) Transfer curve of a device prepared at 2.8 mm/s shearing speed showing mobility of 4.59 cm 2 /Vs.
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TL;DR: The authors would like to thank M. Chabinyc, H. Ade, B. Noriega, K. Vandewal, and D. Duong for fruitful discussions in the preparation of this review and the Center for Advanced Molecular Photovoltaics for funding.
Abstract: The authors would like to thank M. Chabinyc, H. Ade, B. Collins, R. Noriega, K. Vandewal, and D. Duong for fruitful discussions in the preparation of this review. Stanford Synchrotron Radiation Lightsource (SSRL) is a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. This publication was partially supported by the Center for Advanced Molecular Photovoltaics (Award No. KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST).
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References
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28 Jul 2005
TL;DR: PfPMP1）与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。
18,940 citations
IBM1
TL;DR: In this article, the authors present new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of organic thin-film transistors (OTFTs) and discuss progress in the growing field of n-type OTFTs.
Abstract: Organic thin-film transistors (OTFTs) have lived to see great improvements in recent years. This review presents new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of OTFTs. The shifted focus in research from novel chemical structures to fabrication technologies that optimize morphology and structural order is underscored by chapters on vacuum-deposited and solution-processed organic semiconducting films. Finally, progress in the growing field of the n-type OTFTs is discussed in ample detail. The Figure, showing a pentacene film edge on SiO2, illustrates the morphology issue.
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TL;DR: In this article, Zhao et al. used uniaxial tensile strain to tune the 2D and G bands of graphene and obtained a band gap opening of ∼300 meV under 1% tensile tensile stress.
Abstract: Graphene was deposited on a transparent and flexible substrate, and tensile strain up to ∼0.8% was loaded by stretching the substrate in one direction. Raman spectra of strained graphene show significant red shifts of 2D and G band (−27.8 and −14.2 cm−1 per 1% strain, respectively) because of the elongation of the carbon−carbon bonds. This indicates that uniaxial strain has been successfully applied on graphene. We also proposed that, by applying uniaxial strain on graphene, tunable band gap at K point can be realized. First-principle calculations predicted a band-gap opening of ∼300 meV for graphene under 1% uniaxial tensile strain. The strained graphene provides an alternative way to experimentally tune the band gap of graphene, which would be more efficient and more controllable than other methods that are used to open the band gap in graphene. Moreover, our results suggest that the flexible substrate is ready for such a strain process, and Raman spectroscopy can be used as an ultrasensitive method to ...
1,367 citations
01 Jan 2008
TL;DR: In this paper, the authors used the Raman spectra of strained graphene to estimate the band gap opening under 1% uniaxial tensile strain on a transparent and flexible substrate.
Abstract: Graphene was deposited on a transparent andflexible substrate, and tensile strain up to0.8% was loaded by stretching the substrate in one direction. Raman spectra of strained graphene show significant red shifts of 2D and G band (27.8 and14.2 cm 1 per 1% strain, respectively) because of the elongation of the carboncarbon bonds. This indicates that uniaxial strain has been successfully applied on graphene. We also proposedthat,byapplyinguniaxialstrainongraphene,tunablebandgapatKpointcanberealized.First-principle calculations predicted a band-gap opening of300 meV for graphene under 1% uniaxial tensile strain. The strained graphene provides an alternative way to experimentally tune the band gap of graphene, which would be more efficient and more controllable than other methods that are used to open the band gap in graphene. Moreover,ourresultssuggestthattheflexiblesubstrateisreadyforsuchastrainprocess,andRamanspectroscopy can be used as an ultrasensitive method to determine the strain.
1,171 citations