This study focuses on the microstructural modifications of regioregular poly(3-hexylthiophene) (rr-P3HT) in the small active channel of thin-film transistors (TFTs) during operations. Polarized absorption and micro-Raman spectroscopy analyses allow us to probe directly the conformation transitions of rr-P3HT chains parallel or perpendicular to the channel by means of exciton bandwidth, interchain electronic coupling, and effective conjugation length. The results of absorption spectra and a joint experimental-theoretical study of Raman spectra show that an external source-to-drain electric field can align rr-P3HT chains parallel to the channel, improving electrical performance after long-term operations, especially charge transport properties. In comparison, the applied external gate field induced an increase in amorphous fraction of the rr-P3HT films. After the analysis, we propose a chain rearrangement model driven by an external electric field to interpret the changes of the effective conjugation length of rr-P3HT, rather than thermal annealing. Our observations provide a thorough explanation for the previously unknown relationships of structure-electronic properties under the extended operations of polymer TFT devices.
Polycondensation of 4-bis[2-(1-methylpyrrol-2yl)vinyl]-2,5-didodecyloxybenzene and squaric acid yielded the polysquaraine SQ with two isomeric subunits1,3-addition (zwitterionic) and 1,2-addition (diketonic) moietiesin the main chain structure. The former featured a C−O/CO infrared (IR) absorption frequency at 1622 cm −1 ; the latter, a CO signal at 1716 cm −1 . Traditional synthesis yielded SQ as a powder with metallic luster that could not be cast as a polymer film from solution. When the ionic liquid [Oct 3 NMe][TfO] (IL) was present in the cosolvent of BuOH and benzene (1:3), however, the resulting SQI x polymers (x = 0.01−5 wt %) did not precipitate from solution, making it possible to cast continuous free-standing films with a large area (>1 × 1 cm 2 ). A greater content of IL in the solution favored the formation of the 1,3-addition zwitterionic subunits in the SQI x polymer main chains, thereby changing the physical and optical properties of the polysquaraine, as evidenced in IR and optical absorption spectra. The features in the UV−Vis−NIR absorption spectra of SQ and SQI x were dependent on the IL concentration and the nature of the solvent. Among our synthesized SQI x polymers, SQI 0.01 and SQI 0.1 formed flexible free-standing films with metallic luster, smooth surfaces, and good semiconductivities (2.27 × 10 −5 and 4.74 × 10 −5 S/cm, respectively). X-ray diffraction patterns revealed that the presence of IL in the polymerization medium increased the SQI x interchain packing distance. SQI 0.01 and SQI 0.1 possessed thermal stabilities comparable with that of SQ. Our successful use of IL in the preparation of SQI x polymers appears to have great potential for application in ionic liquid−related organic or polymeric preparation and processing.
Ag/ZnO nanorod structure was synthesized by using the hydrothermal method to grow ZnO nanorods and melted silver nonoparticles into ZnO nanorods by thermal annealing process in vacuum at 700 oC. The photocatalytic activity for methylene blue decolorization is enhanced by silver nanoparticles melted into a ZnO nanorod structure owing to the formation of Schottky barrier near the Ag/ZnO interface prolongs the recombination of electron-hole pairs effectively. The size effect of silver nanoparticles in the Ag/ZnO nanorod structure for photocatalytic activity was discussed which was changed from 12 to 34 nm. The smaller silver nanoparticle size sample shows better decolorization efficiency of methylene blue solution owing to the higher surface area of Ag/ZnO nanoroad. Ag/ZnO nanorod films have been characterized by X-ray diffraction (XRD), UV-vis spectroscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The dye decolorization significantly increased from 69 to 99 % after UV light irradiation for 8 hr by the optimum Ag/ZnO nanorod film.
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