Researchers at the University of Liège and the University of Namur have developed an innovative electrochromic material capable of independently regulating light and heat in buildings. Based on a mixed molybdenum-tungsten oxide (MoWOx), this breakthrough paves the way for even more efficient and energy-saving smart windows.
E
lectrochromic windows are intelligent glazings capable of modulating their colouring or, more generally, their state of transparency/opacity when an external electric current is applied to it. This property makes it possible to control the intensity of solar radiation entering a building without the need for blinds or curtains. This type of window is already manufactured industrially and used technologically in some buildings. Still, current products do not allow separate control of visible light (VIS) and near-infrared radiation (NIR), which are linked to incident luminosity and heat, respectively. Researchers at the University of Liège and the University of Namur, with support from the F.R.S.-FNRS, have therefore developed a new formulation of electrochromic material, called MoWOx*, which is based on a "dual-band" functionality that allows selective and independent modulation of incoming light and heat flows.
Through this new formulation, these scientific teams have demonstrated the occurrence of an innovative optical mode, known as 'warm', for the first time for this type of oxide. In this mode, the glass remains transparent to infrared radiation to allow heat to pass through while only partially filtering out visible light. This feature is particularly interesting for cold climates and winter periods, where maximising solar heat gain while reducing solar glare can considerably reduce the energy consumption of buildings, particularly in terms of heating and artificial lighting.
A plasmonic nanomaterial for advanced optical filtration
This "dual-band" functionality is based on the incorporation of nanostructured plasmonic compounds in intelligent glass. A plasmonic material is a material whose free electrons can oscillate collectively under the effect of light. Depending on its composition and structure, it can then selectively absorb, reflect, or scatter light. This innovation lies precisely in the application of these plasmonic properties of MoWOx to the case of intelligent glazing.
On this basis, the composition and morphology of the plasmonic nanostructures directly influence the optical selectivity of the filtering, enabling the glazing to be adapted more precisely to users' needs. "Thanks to this technology, we can adjust the transmission of light and heat through windows in real-time, which represents a giant step towards optimising the energy efficiency of buildings," explains Florian Gillissen, a researcher at the University of Liège and first author of the article published in Advanced Optical Materials(1).
His colleague Professor Michaël Lobet, a F.R.S.-FNRS Research associate and first author of the article published in ACS Applied Optical Materials (2), emphasises the complementary nature of the university consortium: "The theoretical and numerical modelling was carried out at UNamur in Professor Luc Henrard's team, while the synthesis and characterisation of the materials was carried out under the direction of Professor Rudi Cloots and Dr Anthony Maho at the University of Liège. It is these synergies between theoretical modelling and manufacturing that have enabled the characterisation of these MoWOx materials."
Illustration of the absorption measurement of samples in powder form using the Kubelka-Munk method (left), and evolution of the absorption spectrum of a plasmonic material as a function of the nature of its environment. | © ACS
A promising application for the buildings of the future
Future intelligent glazing incorporating these new components could ultimately revolutionise energy management in buildings. At a time when the energy transition remains an absolute priority, these innovative windows will help to achieve carbon neutrality targets and construct buildings with virtually zero energy consumption.
This study was carried out as part of the F.R.S.-FNRS-funded PLASMON EC project, in collaboration between the GREEnMat laboratory at the University of Liège and the Institut de la matière structurée (NISM - Structured Matter Institute) at the University of Namur, in close connection with researchers at the Institut de Chimie de la Matière Condensée in Bordeaux (ICMCB - Institute of Condensed Matter Chemistry). The team now plans to further optimize this technology by improving the stability and switching speed of the material while exploring new manufacturing techniques on a larger scale. At the same time, the study of fundamental processes is continuing in order to feed future applied developments, both for intelligent glazing and for other electronic display and labelling technologies.
* The term MoWOx (Mo1-yWyO3-δ) comes from the chemical composition of the material, which is a mixed oxide of molybdenum (Mo) and tungsten (W). Here's how it's formed:
(1) Florian Gillissen, Michaël Lobet, Jennifer Dewalque, Pierre Colson, Gilles Spronck, Rachel Gouttebaron, Mathieu Duttine, Brandon Faceira, Aline Rougier, Luc Henrard, Rudi Cloots, Anthony Maho, Mixed Molybdenum–Tungsten Oxide as Dual-Band, VIS–NIR Selective Electrochromic Material, Advanced Optical Materials, 13 février 2025. doi.org/10.1002/adom.202401995
(2) Michaël Lobet, Florian Gillissen, Nicolas De Moor, Jennifer Dewalque, Pierre Colson, Rudi Cloots, Anthony Maho, Luc Henrard, Plasmonic Properties of Doped Metal Oxides Investigated through the Kubelka-Munk Formalism, ACS Applied Optical Materials, 3 février 2025. doi.org/10.1021/acsaom.4c00432
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