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Identifier

000401034

Title

Ανάπτυξη και μελέτη καινοτόμων χρωμικών επιστρώσεων και διατάξεων για εφαρμογή σε "Έξυπνα Παράθυρα"

Alternative Title

Growth and study of novel chromic coatings and devices for "Smart Windows"

Author

Λουλουδάκης, Δημήτρης

Thesis advisor

Κυριακίδης, Γεώργιος

Reviewer

Κουδουμάς, Εμμανουήλ
Ηλιόπουλος, Ελευθέριος

Abstract

In recent years, chromic coatings have attracted a lot of interest due to the need for the understanding of the physical mechanisms influencing their response and the optimization of their functionality, because of the large number of new technological applications that can be involved such as optical switches, thermal relays, sensors, transistors, thermochromic and electrochromic windows. This thesis focuses on thermochromic and electrochromic materials and devices based on vanadium and tungsten oxides respectively, emphasis given on the development of "smart windows" for energy saving. In particular, the thesis concerns a parametric study regarding the development of thermochromic and electrochromic materials and the investigation of their functionality so that both the physical mechanisms affecting their response can be understood, and the deposition conditions as well as the basic characteristics that result in optimal functionality, combined with simple and low cost production, can be determined. Chemical vapor deposition and hydrothermal growth have been used for the deposition of the materials, while the basic characterization includes X-ray diffraction, Raman Spectroscopy, Scanning Electron Microscopy, transmittance measurements, X-ray photoelectron spectroscopy and cyclic voltammetry. Vanadium dioxide thin layers were grown for the first time at temperatures as low as 350^oC onto glass substrates with a tin dioxide pre-coating, using an atmospheric pressure chemical vapor deposition system, the layers exhibiting significant thermochromic behavior despite their low crystallinity. The parametric study performed indicated that optimal thermochromic behavior appears in uniform layers of monoclinic vanadium dioxide, its effective growth requiring deposition temperatures of 450-500^oC. Furthermore, reduction of the transition temperature was found possible only with doping: a 1.5% tungsten doping reduced the transition temperature from 68^oC to 44^oC. Vanadium dioxide layers were also grown for first time on flexible glass substrate, the layers exhibiting very good thermochromic properties, a result that can broaden the range of thermochromic applications. In this case, doping with tungsten resulted in a transition temperature of 38^oC. In all cases, correlation of the basic characteristics of the layers with their functionality was performed and as was found out, the thermochromic behavior is strongly affected by the phase, the crystallinity and the surface morphology. Correspondingly, electrochromic layers of tungsten trioxide were grown, using a low pressure chemical vapor deposition system, the layers exhibiting significantly improved coloration efficiency, as compared with others already reported in the literature. The parametric study performed indicated that the electrochemical/electrochromic behavior of the layers depends on basic characteristics such as phase, thickness, crystallinity and preferred growth orientation. Finally, depositions of vanadium pentoxide layers were performed with hydrothermal growth at very low temperatures, 95^oC, where, a strong influence of the pH of the starting solution on the stability and the functionality of the layers was observed.

Language

Greek

Subject

Chemical vapor deposition

Coloration efficiency

Electrochromic layers

Hydrothermal growth

Thermochromic layers

Transition temperature

Tungsten trioxide

Vanadium dioxide

Vanadium pentoxide