Surfactant-free synthesis of sub-stoichiometry tungsten oxide nanoparticles and their use as anode buffer layers in organic solar cells

On-Demand Activation of Photochromic Nanoheaters for High Color Purity 3D Printing

“…The XPS spectra of the pristine WO 3 consist of a doublet peak due to spin–orbit coupling assigned as W 4f 7/2 and W 4f 5/2 with binding energies of 35.9 and 38.1 eV, respectively, which corresponds to W 6+ . Furthermore, the XPS analysis of the W 4f spectra after UV illumination suggests the reduction of the W 6+ to W 5+ which appears as an additional doublet peak shifted 1 eV at lower energies in line with the previous reports studying plasma excitation . We have not observed a complete reduction of the tungsten into W 5+ oxidation state after UV-treatment which confirms that the photoreduction mechanism takes place near the surface of the NCs as previously reported and agrees with the model of the formation of tungsten bronzes being responsible for the photochromic effect …”

“…Carbon black powder was purchased from PlasmaChem. WO 3 was synthesized following the procedure of Brutsch et al and dispersed in a concentrated form in deionized water. This method was selected as it produces small, uncoated nanoparticles with a high surface-to-volume ratio, which has been shown to be advantageous for maximizing the photothermal heating efficiency of nanoparticles, − and will also aid the rate of photochromic excitation, which largely occurs at the particle surface. ,, The small particle size also introduces quantum confinement effects which blueshift the absorption band edge out of the visible, leading to more transparent NPs (in their unexcited state).…”

“…This process has been shown to be highly reversible and stable over thousands of cycles 38 . WO3 NPs are synthesized following the procedure outlined by Brutsch et al 29 and were dispersed in water at a concentration of 3 g/L and their spectra are shown in Fig. 1a along with solutions of CB and GNRs, next to photos of the solutions.…”

“…One of the most promising of these materials is tungsten­(VI) oxide, WO 3 , which has a strong absorption in the NIR that can be efficiently switched on and off using electricity (electrochromic) or ultraviolet radiation (photochromic) . Moreover, WO 3 is stable at high temperatures well above 400 °C , and can be readily synthesized as nanoparticles using cheap reactants. , In this work, we utilize for the first time the photochromic properties of WO 3 NPs to develop a 3D printing method that offers very high color purity and achieves white 3D printed objects via photothermal sintering with low cost NIR light sources.…”

“…27 Moreover, WO 3 is stable at high temperatures well above 400 °C26,28 and can be readily synthesized as nanoparticles using cheap reactants. 29,30 In this work, we utilize for the first time the photochromic properties of WO 3 NPs to develop a 3D printing method that offers very high color purity and achieves white 3D printed objects via photothermal sintering with low cost NIR light sources.…”