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Title: Charge Transport and Thermal Properties of A Semicrystalline Polymer Semiconductor
Keywords: Charge transport, PBTTT, Organic semiconductor, Charge modulation spectroscopy, Organic device, Thermal property
Issue Date: 29-Jul-2010
Citation: ZHAO LIHONG (2010-07-29). Charge Transport and Thermal Properties of A Semicrystalline Polymer Semiconductor. ScholarBank@NUS Repository.
Abstract: The charges residing in molecular pi-conjugated organic semiconductors (OSCs) dissolved in solutions have been well-established spectroscopically to be polarons self-trapped by lattice relaxation. However there is recent evidence that in molecular crystals and in ordered polymer OSC films, they are show a significant delocalization across the pi-conjugated chains. Here we report evidence for a novel polaron delocalization transition that coincides with the ring-twist transition (Tr) in tetradecyl-substituted poly[2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene-2,5-diyl] (PBTTT). We established the existence of an onset temperature for correlated ring twisting along the polymer chain through a combination of electronic, infrared and Raman vibrational spectroscopies, which have been supported by quantum chemical calculations. We then established that the field-induced polarons become more delocalized across the Tr transition from their infrared and optical charge-modulation spectra in field-effect transistors. This surprising effect arises from the suppression of the intrachain lattice relaxation of the polarons which promotes their interchain delocalization across coherent segments. However electrical characteristics reveal that these polarons are still confined by thermal disorder on a longer length scale in a Gaussian-like density-of-states (DOS). Therefore polymer OSCs can support delocalized polarons that are now appear close to the boundary of band transport. A corollary of these results is the importance of suppressing electron?lattice coupling to promote the required polaron delocalization that may ultimately reach band transport.
Appears in Collections:Ph.D Theses (Open)

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