Optical anisotropy of aligned pentacene molecules on a rubbed polymer corresponding to the electrical anisotropy
TL;DR: In this paper, the optical anisotropic properties of a pentacene film on a rubbed polyvinylalcohol (PVA) layer were investigated and the electrical performances of the OFETs were correlated with the optical properties of the PVA layer.
About: This article is published in Current Applied Physics.The article was published on 2010-01-01. It has received 14 citations till now. The article focuses on the topics: Pentacene & Anisotropy.
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TL;DR: In this article, a method of strain-aligning polymer films is introduced and applied to regioregular poly(3-hexylthiophene) (P3HT), showing several important features of charge transport.
Abstract: A novel method of strain-aligning polymer films is introduced and applied to regioregular poly(3-hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge-mobility anisotropy, where the in-plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two-dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane-on and edge-on packing configurations, as the strain alignment is found to induce a significant face-on orientation of the originally highly edge-on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge-mobility anisotropy of 9, providing a simple and effective method to investigate charge-transport mechanisms in polymer semiconductors.
286 citations
234 citations
TL;DR: In this article, the properties of zinc oxide thin films on soda-lime glass substrate via dip-coating technique, using zinc acetate dehydrate and ethanol as raw materials, have been investigated using XRD, SEM and UV-Vis spectrophotometer.
26 citations
TL;DR: In this article, the authors systematically studied how the mobility in a pentacene thin-film transistor (TFT) with an anisotropic polymeric insulator is decisively dependent on the deposition rate of Pentacene molecules.
Abstract: We systematically studied how the mobility in a pentacene thin-film transistor (TFT) with an anisotropic polymeric insulator is decisively dependent on the deposition rate of pentacene molecules. This occurs from the view point of both the morphological coverage and optical phase retardation. Until a value of 2 A/s, as the deposition rate increases, the alignment of pentacene molecules, examined by optical retardation improves due to the guaranteed diffusion process for more stable positioning and an improved packing density at an early stage. The corresponding mobility is found to be proportional to the deposition rate in this regime. For increased deposition rates above 2 A/s, due to the shortage of diffusion processing time, evaporating pentacene molecules damage the pre-deposited and pre-aligned pentacene molecules on the anisotropic insulator. Thus, the optical retardation starts to decrease definitely when the early stage packing density is saturated. The resultant mobility is found to be inversely proportional to the deposition rate. Based on the morphological, optical results and the corresponding mobility, we confirm that the deposition rate of an organic semiconductor has a critical effect on the structural orientation, the molecular growth, and the resultant mobility in organic TFTs.
14 citations
Cites background or methods from "Optical anisotropy of aligned penta..."
...Recently, the alignment of pentacene molecules along the rubbed direction of polymers was reported [8,9,22]....
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...In order to determine the optical anisotropy, which represents the degree of alignment capability, a photoelastic modulator (PEM) (Hinds, PEM-90) was used [22]....
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...In order to generate the anisotropic property, a rubbing process for the PVA layer was conducted by a commercial rubbing machine with a cotton velvet material at a roller speed of 500 rpm [22]....
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...In addition, the PEM method was recently introduced as a new technique to examine the aligning features of pentacene molecules [22]....
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TL;DR: In this article, the authors report on the enhancement of the field-effect mobility of solution-processed 6,13-bis(triisopropylsilylethynyl)-pentacene by unidirectional topography (UT) of an inkjet-printed polymer insulator.
Abstract: We report on the enhancement of the field-effect mobility of solution-processed 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) by unidirectional topography (UT) of an inkjet-printed polymer insulator. The UT leads to anisotropic spreading and drying of the TIPS-pentacene droplet and enables to spontaneously develop the ordered structures during the solvent evaporation. The mobility of the UT-dictated TIPS-pentacene film (0.202 ± 0.012 cm2/Vs) is found to increase by more than a factor of two compared to that of the isotropic case (0.090 ± 0.032 cm2/Vs). The structural arrangement of the TIPS-pentacene molecules in relation to the mobility enhancement is described within an anisotropic wetting formalism. Our UT-based approach to the mobility enhancement is easily applicable to different classes of soluble organic field-effect transistors by adjusting the geometrical parameters such as the height, the width, and the periodicity of the UT of an inkjet-printed insulator.
10 citations
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TL;DR: Anisotropic charge carrier mobility in oriented conjugated polymers has been investigated using a field effect transistor in this article, where a thin polymer film is put onto the transistor substrate parallel or perpendicular to the conduction channel.
35 citations
TL;DR: In this paper, preferential in-plane molecular orientation and charge transport anisotropy in pentacene thin film transistors achieved by using a photo-aligned polyimide film with large inplane anisotropic.
Abstract: The authors report preferential in-plane molecular orientation and charge transport anisotropy in pentacene thin film transistors achieved by using a photoaligned polyimide film with large in-plane anisotropy. Polarized infrared absorption spectra indicated that the molecular plane normal of the pentacene preferentially aligned along the average orientation direction of the underlying polyimide backbone structure. Atomic force microscope images showed that the alignment of the polyimide backbone structure significantly modified the pentacene growth process and remarkably increased the grain size. The charge carrier mobility along the polyimide alignment direction was about twice of that perpendicular to it.
32 citations
TL;DR: In this paper, a phase modulation method using a photoelastic modulator was employed to determine the uniformity and quality of the alignment layer of liquid crystal (LC) molecules.
Abstract: We have employed a phase modulation method using a photoelastic modulator to determine the uniformity and quality of the alignment layer of liquid crystals (LCs). It is demonstrated that a two-dimensional map of the phase retardation, associated with irregular rubbing and/or chemical contaminants, provides invaluable information about an early detection of defects involved for aligning the LC molecules on a substrate.
23 citations
TL;DR: In this paper, the underlying mechanism for the mobility enhancement in a pentacene thin-film transistor (TFT) with a photocrosslinking polymeric insulator, poly(vinyl cinnamate) (PVCi), is presented.
Abstract: We present the underlying mechanism for the mobility enhancement in a pentacene thin-film transistor (TFT) with a photocrosslinking polymeric insulator, poly(vinyl cinnamate) (PVCi). Experimental results for the optical anisotropy, x-ray diffraction, and microscopic layer-by-layer coverage of the pentacene film on the photocrosslinked PVCi layer, exposed to a linearly polarized ultraviolet (LPUV) light, clearly demonstrate the importance of the structural packing of pentacene grains rather than the directional alignment of the pentacene molecules for the mobility enhancement. The packing density of pentacene grains is directly related to the number of photocrosslinking sites of the PVCi insulator produced by the LPUV. It is found that the mobility in the pentacene TFT is linearly proportional to the number of photocrosslinked sites of the PVCi insulator serving as interaction sites for the layer-by-layer coverage of the pentacene molecules with no preferred orientation.
23 citations
TL;DR: In this paper, the importance of the functional group density of polymeric insulators (PI) for organic thin-film-transistors (OTFTs) in terms of the insulator processing temperature and the exposure of a linearly polarized ultraviolet (LPUV) light was described.
Abstract: We describe the importance of the functional group density of polymeric insulators (PI) for organic thin-film-transistors (OTFTs) in terms of the insulator processing temperature and the exposure of a linearly polarized ultraviolet (LPUV) light. The PI layers processed at lower temperatures than the boiling temperature (Tb) of the solvent have higher densities of functional groups than those processed above Tb. The carrier mobility in the pentacene OTFT processed below Tb increases at least by a factor of three with maintaining other electrical properties such as the threshold voltage and the current on/off ratio. Our results suggest that the preferential alignment of the pentacene molecules is not the main physical mechanism for the mobility enhancement. From the mobility anisotropy resulting from the polarization of the LPUV, the packing density of the pentacene molecules on the PI layer, dictated primarily by the density of functional groups, is found to play a critical role on the magnitude of the mobility.
19 citations