Electron and Ambipolar Transport in Organic Field-Effect Transistors
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ABSTRACT: Indigoids have received much attention as the candidates of sustainable ambipolar organic semiconductor. However, the low charge carrier mobilities extremely limit their practical applications. Therefore, in-depth understanding of their electronic-structure properties and rational molecular modifications are urgently required. Here, we propose a promising strategy to design ambipolar organic semiconductors based on indigo fragments. Moreover, we predicted the organic crystal structures by evolutionary algorithm combined with DFT-D method. Charge transport properties have been significantly improved for the designed molecules, such as narrower energy gaps, higher electron affinity, larger transfer inte-grals as well as much smaller reorganization energies for hole and electron. Thusly, remarkable ambipolar charge transport behavior has been predicted, for example, the charge carrier mobilities are up to h /l e = 7.71/5.42 cm2V-1s-1 for NN-indigo-6,6 0-2CN and l h /l e = 5.15/2.13 cm2V-1s-1 for C 9-NN-indigo-6,6 0-2CN respectively.Organic Electronics 05/2015; 24(2015):12-25. DOI:10.1016/j.orgel.2015.05.021 · 3.68 Impact Factor
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ABSTRACT: Diketopyrrolopyrroles (DPPs) have recently gained attention as building-blocks for organic semiconducting polymers and small molecules, however the semiconducting properties of their hydrogen-bonded (H-bonded) pigment forms have not been explored. Herein we report on the performance of three archetypical H-bonded DPP pigments, which show ambipolar carrier mobilities in the range 0.01-0.06 cm(2)/V s in organic field-effect transistors. Their semiconducting properties are correlated with crystal structure, where an H-bonded crystal lattice supports close and relatively cofacial π-π stacking. To better understand transport in these systems, density functional theory calculations were carried out, indicating theoretical maximum ambipolar mobility values of ∼0.3 cm(2)/V s. Based on these experimental and theoretical results, H-bonded DPPs represent a viable alternative to more established DPP-containing polymers and small molecules where H-bonding is blocked by N-alkylation.Organic Electronics 12/2014; 15(12). DOI:10.1016/j.orgel.2014.09.038 · 3.68 Impact Factor
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ABSTRACT: Organic crystalline semiconductors with highly ordered molecular packing could be vital components in novel low power consumption light sensors due to their unique light absorption and charge carrier transport properties. In this work, we show that nanofibers made from naphthyl end-capped bithiophenes can be used for low-voltage, high responsivity organic phototransistors (OPTs). Density functional theory (DFT) calculations have been carried out to estimate the device properties related to charge transport and photon absorption. In terms of the calculation of the reorganization energy upon charge transfer, we used an extended method to include inter-molecule interactions. Experimentally, the device performance of the 5,5-bis(naphthyl)-2,2'-bithiophene (NaT2) nanofiber OPTs has been compared with that of a thin film OPT with inferior molecular ordering. The better photoresponsivity of the nanofiber OPT compared with the thin film OPT under monochromatic illumination at various wavelengths suggests that the NaT2 nanofiber-based OPTs have great potential to be used as high performance nano-scale light detectors. Moreover, the absorption of the nanofiber-based OPTs is also polarization sensitive, which provides another advantage of nanofiber-based devices in terms of potential novel sensor design.Organic Electronics 06/2014; 15(6). DOI:10.1016/j.orgel.2014.02.023 · 3.68 Impact Factor