https://eva.fing.edu.uy/pluginfile.php/55828/mod_resource/content/1/kalogiru.pdf

Solar thermal collectors and applications

Transparent conductors as solar energy materials: A panoramic review

A Review on Photovoltaic/Thermal Hybrid Solar Technology

Electrochromic (EC) materials are able to change their optical properties, reversibly and persistently, by the application of an electrical voltage. These materials can be integrated in multilayer devices capable of modulating the optical transmittance between widely separated extrema. We first review the recent literature on inorganic EC materials and point out that today's research is focused on tungsten oxide (colouring under charge insertion) and nickel oxide (colouring under charge extraction). The properties of thin films of these materials are then discussed in detail with foci on recent results from two comprehensive investigations in the authors' laboratory. A logical exposition is obtained by covering, in sequence, structural features, thin film deposition (by sputtering), electronic band structure, and ion diffusion. A novel conceptual model is given for structural characteristics of amorphous W oxide films, based on notions of defects in the ideal amorphous state. It is also shown that the conduction band density of states is obtainable from simple electrochemical chronopotentiometry. Ion intercalation causes the charge-compensating electrons to enter localized states, implying that the optical absorption underlying the electrochromism can be described as ensuing from transitions between occupied and empty localized conduction band states. A fully quantitative theory of such transitions is not available, but the optical absorption can be modeled more phenomenologically as due to a superposition of transitions between different charge states of the W ions (6+, 5+, and 4+). The Ni oxide films were found to have a porous structure comprised of small grains. The data are consistent with EC coloration being a surface phenomenon, most likely confined to the outer parts of the grains. Initial electrochemical cycling was found to transform hydrated Ni oxide into hydroxide and oxy-hydroxide phases on the grain surfaces. Electrochromism in thus stabilized films is consistent with reversible changes between Ni hydroxide and oxy-hydroxide, in accordance with the Bode reaction scheme. An extension of this model is put forward to account for changes of NiO to Ni2O3. It was demonstrated that electrochromism is associated solely with proton transfer. Data on chemical diffusion coefficients are interpreted for polycrystalline W oxide and Ni oxide in terms of the lattice gas model with interaction. The later part of this review is of a more technological and applications oriented character and is based on the fact that EC devices with large optical modulation can be accomplished essentially by connecting W-oxide-based and Ni-oxide-based films through a layer serving as a pure ion conductor. Specifically, we treat methods to enhance the bleached-state transmittance by mixing the Ni oxide with other oxides characterized by wide band gaps, and we also discuss pre-assembly charge insertion and extraction by facile gas treatments of the films, as well as practical device manufacturing and device testing. Here the emphasis is on novel flexible polyester-foil-based devices. The final part deals with applications with emphasis on architectural “smart” windows capable of achieving improved indoor comfort jointly with significant energy savings due to lowered demands for space cooling. Eyewear applications are touched upon as well.

/pdf/electrochromics-for-smart-windows-thin-films-of-tungsten-aw0rai8h60.pdf

Electrochromics for smart windows: thin films of tungsten oxide and nickel oxide, and devices based on these

We demonstrate the controlled growth of high aspect ratio anatase TiO2 nanorods by hydrolysis of titanium tetraisopropoxide (TTIP) in oleic acid (OLEA) as surfactant at a temperature as low as 80 °C. Chemical modification of TTIP by OLEA is proven to be a rational strategy to tune the reactivity of the precursor toward water. The most influential factors in shape control of the nanoparticles are investigated by simply manipulating their growth kinetics. The presence of tertiary amines or quaternary ammonium hydroxides as catalysts is essential to promote fast crystallization under mild conditions. The novelty of the present approach relies on the large-scale production of organic-capped TiO2 nanocrystals to which standard processing of colloidal nanocrystals, such as surface ligand exchange, can be applied for the first time. Concentrated colloidal titania dispersions can be prepared for a number of fundamental studies in homogeneous solutions and represent a new source of easily processable oxide materia...

Low-Temperature Synthesis of Soluble and Processable Organic-Capped Anatase TiO2 Nanorods

Hybrid photovoltaic/thermal solar systems

Effect of the tungsten oxidation states in the thermal coloration and bleaching of amorphous WO3 films

Deposition and optical properties of optimised ZnS/Ag/ZnS thin films for energy saving applications

Copyright (c) 1997 Elsevier Science S.A. All rights reserved. Dielectric/Metal/Dielectric (D/M/D) thin films deposited on glass offer the possibility of significant energy savings in buildings and can find other applications as components of advanced materials design. In an effort to reduce the complexity and cost of production of D/M/D films, physical vapour deposition was used for the laboratory manufacture of ZnS/Ag/ZnS films on glass. ZnS was used because of its high refractive index, ease of deposition and low cost; Ag was used because of its low absorption in the visible spectrum. The films produced were of good quality, with luminous transmittance as high as 83.9%, IR reflectance above 90% and total hemispherical emittance equal to 6%. The ZnS layers were found not only to antireflect the Ag layer, but also to stabilise the ZnS/Ag/ZnS film, improve its adherence on glass and increase the film thermal resistance up to 240°C. A multipurpose computational optics tool based on the characteristic matrix formulation has been developed for the design and optimisation of the D/M/D films: The optimum thickness of each dielectric layer required to maximise the film luminous transmittance for a given metal layer thickness was established. The optical properties of the films designed were also predicted and the most suitable materials were identified. The optical properties of the films produced were measured and were found to compare favourably with the theoretical predictions. © 1997 Elsevier Science S.A.

P. Yianoulis

Papers

Hybrid photovoltaic/thermal solar systems

Effect of the tungsten oxidation states in the thermal coloration and bleaching of amorphous WO3 films

Deposition and optical properties of optimised ZnS/Ag/ZnS thin films for energy saving applications

Deposition and optical properties of optimised ZnS/Ag/ZnS thin films for energy saving applications

Degradation mechanisms of Pt counter electrodes for dye sensitized solar cells