ICMCTF2017 Session C3-1: Thin Films for Energy-related Applications

There is renewed interest in combining solar photovoltaic technologies with thermally insulating glazings. Modern cities have multi storey buildings with large areas of glazed facades that represent the majority of the building envelope. These facades have large energy exchanges with the environment that must be managed efficiently in order to avoid major energy wastage. The combination of PV technologies with thermal insulating glazings is a novel approach with potential to increase the harvesting of solar energy while minimising unwanted energy exchanges. New technologies for PV such as perovskite cells have shown good efficiency while allowing for some useful residual light transmission with an options for a choice of colour. There is a synergy with double glazed insulating units, first because of the local generation of energy while minimising losses, and second because the perovskite cells are moisture sensitive. In a synergistic design the thermal insulating glazing can act as a protective encapsulation of the cells. Recent advances and the current status of available technologies in this area will be discussed in this paper .

Thermochromic vanadium dioxide (VO₂) undergoes a fully reversible semiconductor-metal transition (SMT) at a critical temperature T_t of ~68 °C with a dramatic change in electric and optical properties, which makes it an attractive candidate for use in smart windows. Switchable VO₂ and W-doped vanadium dioxide (W_xV_1-xO₂) thin films are grown successfully over quartz substrates via electron beam evaporation technique by using VO₂ / W_xV_1-xO₂ as targets at room temperature (RT) followed by a post annealing process at different temperatures. The films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM) and optical transmittance measurement. The XRD analysis shows that the as-deposited films are amorphous, and that transform into (011)-preferred orientation of monoclinic VO₂ (VO₂(M)) after annealing at 500 °C under vacuum. Moreover, (011) peak of W-doped VO₂ films shifts to a lower diffraction angle as compared with un-doped VO₂ films which confirm the incorporation of W ions into the VO₂ lattice. Temperature dependent optical transmittance (T-T) measurement demonstrates the thermochromic properties, with a reduction in the phase transition temperature (T_t) as observed in W-doped VO₂ films, which is attributed to the variation of electron structure in VO₂ due to doping.

The electrical conductivity changes in metal oxides when exposed to atmosphere have attracted considerable interest in the field of gas sensing. Several candidate metal oxides (SnO₂, ZnO, TiO₂ and Ga₂O₃, WO₃) have high sensitivity to gases. Among these metal oxide, Gallium oxide (Ga₂O₃), the stable oxide of gallium, finds attractive applications in luminescent phosphors, high temperature sensors, antireflection coatings, and solar cells. Ga₂O₃ has been recognized as a deep ultraviolet transparent conducting oxide (UV–TCO), which makes the material a potential candidate for transparent electrode applications in UV optoelectronics. Ga₂O₃ thin film has proven to detect the presence of oxygen at high temperatures (>700 °C). However, recent trends and demand for reliable oxygen sensors imposed restrictions on the response time and sensitivity. In this work, we proposed and investigate to modify the properties of Ga₂O₃ by selectively doping with titanium (Ti). Ti doped β- Ga₂O₃ thin films with variable Ti content were deposited by co-sputtering of the Ga-oxide ceramic and Ti metal by varying the sputtering power to these targets. The effect of Ti on the crystal structure and electronic properties of β- Ga₂O₃ thin films is significant. The results will be presented and discussed in the context of utilizing these materials in oxygen sensor applications.