Improvement of Transparent Conducting Performance on Oxygen-Activated Fluorine-Doped Tin Oxide Electrodes Formed by Horizontal Ultrasonic Spray Pyrolysis Deposition.

In this study, highly transparent conducting fluorine-doped tin oxide (FTO) electrodes were fabricated using the horizontal ultrasonic spray pyrolysis deposition. In order to improve their transparent conducting performances, we carried out oxygen activation by adjusting the ratio of O2/(O2+N2) in the carrier gas (0%, 20%, and 50%) used during the deposition process. The oxygen activation on the FTO electrodes accelerated the substitution concentration of F (FO•) into the oxygen sites in the FTO electrode while the oxygen vacancy (VO••) concentration was reduced. In addition, due to growth of pyramid-shaped crystallites with (200) preferred orientations, this oxygen activation caused the formation of a uniform surface structure. As a result, compared to others, the FTO electrode prepared at 50% O2 showed excellent electrical and optical properties (sheet resistance of ∼4.0 ± 0.14 Ω/□, optical transmittance of ∼85.3%, and figure of merit of ∼5.09 ± 0.19 × 10-2 Ω-1). This led to a superb photoconversion efficiency (∼7.03 ± 0.20%) as a result of the improved short-circuit current density. The photovoltaic performance improvement can be defined by the decreased sheet resistance of FTO used as a transparent conducting electrode in dye-sensitized solar cells (DSSCs), which is due to the combined effect of the high carrier concentration by the improved FO• concentration on the FTO electrodes and the fasted Hall mobility by the formation of a uniform FTO surface structure and distortion relaxation on the FTO lattices resulting from the reduced VO••• concentration.

Fast-switching electrochromic properties of mesoporous WO3 films with oxygen vacancy defects.

In this study, mesoporous WO3 films with oxygen vacancy defects have been fabricated using the camphene-assisted sol-gel method. By controlling the optimized weight ratio of camphene on the WO3 films, we developed a unique film structure of the WO3 phase with both mesoporous morphology and oxygen vacancy defects due to the distinctive effect of camphene. The mesoporous WO3 films with oxygen vacancy defects fabricated using 10 wt% camphene showed superb multifunctional electrochromic (EC) properties with both fast switching speeds (5.8 s for coloration speed and 1.0 s for bleaching speed) and high coloration efficiency (CE, 51.4 cm2 C-1), which include the most prominent properties, particularly for switching speeds among WO3-based films reported so far. The attractive EC properties are due to the synergistic effects of the mesoporous morphology and oxygen vacancy defects on the WO3. The fast switching speeds are mainly caused by the reduced Li+ diffusion pathway due to the mesoporous morphology and increased electrical conductivity due to the oxygen vacancy defects. In addition, the increased CE value is due to the large transmittance modulation as a result of a more effective electrostatic contact of the mesoporous morphology and an increased optical bandgap of the oxygen vacancy defects on the WO3. Therefore, this unique film structure of the mesoporous WO3 films with oxygen vacancy defects can be potentially regarded as a novel EC material for high-performance EC devices.

Activated mesoporous carbon nanofibers fabricated using water etching-assisted templating for high-performance electrochemical capacitors.

Activated mesoporous carbon nanofibers (AMCNFs) are synthesized by a sequential process of electrospinning, water etching-assisted templating, and acid treatment. Their morphologies, crystal structures, melting behavior, chemical bonding states, surface properties, and electrochemical performance are investigated for three different polyacrylonitrile (PAN) to polyvinylpyrrolidone (PVP) weight ratios - PAN : PVP = 8 : 2, 7 : 3, and 6 : 4. Compared to other samples, the AMCNFs with an optimum weight ratio of 6 : 4 show the highest specific surface area of 692 m(2) g(-1), a high volume percentage of mesopores of 43.9%, and an increased amount of carboxyl groups (10.5%). This results in a high specific capacitance of 207 F g(-1), a high-rate capability with a capacitance retention of 93%, a high energy density of 24.8-23.1 W h kg(-1), and an excellent cycling durability of up to 3000 cycles. The electrochemical performance improvement can be explained by the combined effect of the high surface area relative to the increased electrical double-layers, the high volume fraction of mesopores relative to shorter diffusion routes and low resistance pathways for ions, and the increased amount of carboxyl groups on the CNF surface relative to enhanced wettability.

Surface modification and characterization of electrosprayed Sn-doped In2O3 thin films.

We synthesized Sn-doped In2O3 (Indium tin oxide, ITO) thin films using electrospray and spin-coating. Scanning electron microscopy, atomic force spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Hall-effect measurement, and UV-vis spectrophotometry measurements were performed to investigate the morphological, structural, chemical, electrical, and optical properties of the electrosprayed ITO films with a sol-layer coating for surface modification. To obtain the optimum performance of the resultant ITO thin films after surface modification, we heat-treated them at four different temperatures of 450 degrees C (sample A), 550 degrees C (sample B), 650 degrees C (sample C), and 750 degrees C (sample D) using microwave heating. Surface modified ITO thin films calcined at 550 degrees C (sample B) using electrospray and spin-coating are observed to have superior resistivity (9.9 x 10(-3) 2 Ω x cm) and optical transmittance (-92.08%) owing to the improved densification of the ITO surface by spin-coating and the formation of uniform ITO thin films by electrospraying.

Synthesis and characterisation of polygonal indium tin oxide nanocrystals.

Polygon ITO (Sn-doped In2O3) nanocrystals were synthesised via electrospinning, and their morphology, structural properties, and chemical composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). To determine the optimum conditions for the fabrication of polygon ITO nanocrystals, calcination temperature after the electrospinning process was controlled at 500 degrees C, 600 degrees C, 700 degrees C, and 800 degrees C, and the amount of PVP polymer was controlled at 4 wt%, 7 wt%, and 10 wt%. For comparison purposes, single In2O3 nanocrystals were also synthesised via electrospinning and calcination. The results show that ITO nanocrystals fabricated at a calcination temperature of 800 degrees C and with 10 wt% of PVP polymer exhibit clear polygon structure with single-crystallinity, which may be explained in terms of the effect of Sn doping in the In2O3 matrix and the oriented aggregation and Oswald ripening growth during the fusion process of ITO nanocrystals.