Fabrication and Performance Evaluation of a Nanostructured ZnO-Based Solid-State Electrochromic Device.

In this study, we present an all-solid-state electrochromic device (ECD) that eliminates the need for hard-to-obtain materials and conventional liquid/gel electrolytes. Using a cost-effective and industrially scalable spray coating technique, we developed an ECD containing a layer of zinc oxide nanorods (ZnOnano) synthesized via a simple solochemical route. The device configuration includes a preformed Al-coated glass substrate, acting as a counter electrode, within a glass/Al/ZnOnano/PEDOT:PSS architecture. The device exhibits reversible switching between light blue and dark blue states upon application of -1.2 V and +2.8 V, respectively, with a significant difference in transmittance between bleached and colored states in the visible-NIR spectrum, featuring a high coloration efficiency of 275.62 cm2/C at 600 nm. The response times required for both coloring and bleaching states were 9.92 s and 7.51 s, respectively, for a sample with an active area of 5.5 × 2.5 cm2. Regarding the electrochemical stability of the ZnO-based ECD, the transmittance modulation reached around 8.01% at 600 nm after 12,800 s, following initial variations observed during the first 10 cycles. These results represent significant progress in electrochromic technology, offering a sustainable and efficient alternative to traditional ECDs. The use of economical fabrication techniques and the exclusion of critical materials highlight the potential for widespread industrial adoption of this novel ECD design.

Effect of reaction parameters on the formation and properties of ZnO nanocrystals synthesized via a rapid solochemical processing.

ZnO nanocrystals were successfully prepared under mild conditions by solochemical method from sodium hydroxide and zinc nitrate hexahydrate in 3 h refluxing. In this process the dependence of the morphologies, sizes and formation mechanisms of the ZnO nanocrystals on the reaction temperature was investigated. The samples were analyzed by X-ray diffraction (XRD), including Rietveld analyses, transmission electron microscopy (TEM), Raman spectroscopy and UV-Visible absorption spectroscopy. The X-ray diffraction patterns revealed that the formed products are pure ZnO with hexagonal (wurtzite) structure. Rietveld analyses of the XRD patterns showed anisotropic effects on the size and microstrain of ZnO nanocrystals. The anisotropy on the crystallite size decreases as the reaction temperature increases. The microstrain remains constant up to 90 degrees C when reached highest values in all directions. The transmission electron microscopy images showed short ZnO nanorods and rounded shape nanoparticles for all samples. The average size (length by diameter) ratio of the ZnO nanorod increased from 1.5 to 2.4 when reaction temperature was raised from 50 degrees C to 80 degrees C and decreased to 1.4 as the temperature was further increased to 90 degrees C. The HRTEM image of the sample prepared at 90 degrees C showed that ZnO nanocrystals have their c-axes as the primary growth direction. The wurtzite structure in ZnO nanorods has been verified by its characteristic E2 mode in the Raman spectra of all samples. All Raman peaks (especially for E2 mode) observed for the sample prepared at 90 degrees C showed huge intensity reduction and linebroadening, except for the second order Raman mode at about 1068 cm(-1) which presented a very huge and unusual increase on intensity. All samples presented a blue shift in the excitonic absorption compared to ZnO bulk that increases alongside with reaction temperature. In addition a mechanism for the synthesis of ZnO nanocrystals using zinc nitrate hexahydrate and sodium hydroxide by the solochemical method has also been proposed.

Effects of reaction temperature on structural properties of ZnO nanocrystals prepared via solochemical technique.

In this research, ZnO nanocrystals were prepared in a few hours by solochemical processing using sodium hydroxide and zinc nitrate hexahydrate as raw materials. Different reaction temperatures have been investigated and revealed their effects on the crystallite size, morphology and crystalline phase of ZnO nanocrystals. Materials synthesized by this technique were investigated employing X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV-Visible spectroscopy and Rietveld method. XRD and TEM showed that the ZnO samples are formed by a single hexagonal phase of wurtzite structure containing predominantly rod-like particles, except for the sample obtained at 90 degrees C that is basically formed by rounded nanometric particles. The sample obtained at 90 degrees C presented the smallest average crystallite size (approximately 20 nm) and the highest blue shift between the UV-Vis absorption spectra of the samples when compared to that of ZnO bulk. These size/disorder effects can also explain the attenuation of the ZnO Raman spectrum with increase of reaction temperature.

The rapid preparation of ZnO nanorods via low-temperatures solochemical method.

Substantial efforts have been devoted towards researching routes that provide an appropriate and simple approach for the production of zinc oxide (ZnO) nanocrystals. Here, a rapid and inexpensive solochemical method was employed to synthesize ZnQ nanocrystals through the decomposition of zinc chloride (ZnCl2) and sodium hydroxide (NaOH) at 50 degrees C, 70 degrees C and 90 degrees C. The powders were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The products showed high purity, nearly uniform rod-like morphology and nanometric crystallite sizes. With increasing reaction temperature, the crystallites become smaller and rounded. The Raman results reveal correlations between Raman line widths and intensities with ZnO nanorods dimensions. More specifically, the line widths are large and therefore less intense as the nanorod becomes smaller.

Production and characterization of ZnO nanocrystals obtained by solochemical processing at different temperatures.

The semiconductor zinc oxide (ZnO) has been widely used because it presents exclusive novel physical and chemical properties at the nanometer scale. In this work, ZnO nanocrystals were synthesized via solochemical processing in a few hours without any subsequent treatment. ZnCl2 and NaOH were adopted as synthesis precursors. ZnO production was realized at different reaction temperatures to verify the effect of this parameter on synthesis. The synthesis temperatures studied were 50 degrees C, 70 degrees C and 90 degrees C. The materials obtained at different reaction temperatures were characterized by X-ray diffraction (XRD) and the Rietveld method. The size and morphology of the ZnO particles obtained at 50 degrees C were evaluated by transmission electron microscopy (TEM). ZnO powders have hexagonal wurtzite structure and nanometric-sized crystallites. Microstrain increased and the average crystallite size decreased with the increase in reaction temperature.