Original Research ARTICLE
Transparent TiO2 and ZnO thin films on glass for UV protection of PV modules
- 1Department of Built Environment and Energy Technology, Linnaeus University, Sweden
- 2Department of Applied Physics, School of Engineering, Royal Institute of Technology, Sweden
- 3Department of Engineering Sciences, Uppsala University, Sweden
- 4RISE Glass section, RISE Research Institutes of Sweden, Sweden
Failure of PV modules frequently occurs as a result of degradation of its encapsulation by destructive UV radiation. Both the life expectancy and efficiency of PV modules can be improved by reducing the transmittance of the destructive UV radiation through the cover glass without compromising the transmittance in the visible wavelength region. In addition, if the absorbed UV photons can be down-shifted to wavelengths that can be more efficiently converted to electrical energy, an additional increase of the PV efficiency could be achieved. In this study we have investigated transparent ZnO and TiO2 thin films deposited by spray pyrolysis on soda lime silicate float glass as functional layers on PV cover glass. The optical bandgap, UV-cutoff, UV-Vis transmittance, reflectivity (total and diffuse) and photoluminescence have been determined. The ZnO coating shifted the optical bandgap to longer wavelengths, resulting in a reduction of the transmittance of destructive UV radiation by up to approximately 85 %. Distinct photoluminescence peak at 377 nm and at 640 nm were observed for one of the ZnO samples. The TiO2 coated glasses also showed an increased UV cut-off, which resulted in a reduction of transmittance of destructive UV radiation by up to 75%. However, no photoluminescence peaks could be observed from the TiO2 films with 325 nm excitation laser and can be explained by the fact that only indirect interband transitions are accessible at this excitation wavelength. Deposition of both ZnO and TiO2 coatings resulted in a reduction of the transmitted light convertible by PV modules, by up to 12.3 and 21.8%, respectively. The implication of the results is discussed in terms of lifetime expectancy and efficiency of PV modules.
Keywords: float glass, thin films, UV protection, Photovoltaic modules (PV), cover glass, transparent intelligence, solar energy materials, Photoluminescence (PL)
Received: 30 Nov 2018;
Accepted: 30 Sep 2019.
Copyright: © 2019 Johansson, Peralta, Jonson, Anand, Österlund and Karlsson. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Stefan Karlsson, RISE Glass section, RISE Research Institutes of Sweden, Växjö, SE-351 96, Sweden, Stefan.Karlsson@ri.se