Combinatorial exploration of thermochromic thin films in V-M1-M2-O systems

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This project addresses the exploration of VO2-based thermochromic thin films in V-M1-M2-O systems (M1, M2: e.g. W, Mg, Er, Li) for future application in smart windows. Films to be developed will show high luminous transmittance (Tlum) and solar irradiation modulation (ΔTsol) upon a reversible phase transformation around room temperature. Addition of third elements can decrease the transition temperature (Tc) and improve the thermochromic performance (Tlum and ΔTsol) of VO2-based phases: e.g. W can effectively decrease Tc of VO2 (68°C), but Tlum and ΔTsol are deteriorated; alkaline and rare-earth metals improve Tlum but do not lower substantially Tc. Therefore, a multidimensional search space needs to be explored in order to identify a new multinary material which fulfils all necessary requirements. Thus, to achieve better performance of VO2-based thin films for smart windows, first, V-M1-O systems with unexplored elements for M1 will be investigated in search for elements which reduce Tc and improve Tlum. Then, quaternary systems (V-M1-M2-O) will be explored: synergistic effects of M1 and M2 on the thermochromic properties of VO2 are expected, to achieve lower Tc and higher Tlum. This needs a large experimental dataset which will be accomplished by synthesis of combinatorial materials libraries and their high-throughput characterization. The best identified systems will additionally be fabricated as nanoporous films by glancing angle deposition in order to further enhance Tlum, and a protective antireflective coating will be applied to further optimize Tlum.