Linear topology in amorphous metal oxide electrochromic networks obtained via low-temperature solution processing


Amorphous transition metal oxides are recognized as leading candidates for electrochromic window coatings that can dynamically modulate solar irradiation and improve building energy efficiency. However, their thin films are normally prepared by energy-intensive sputtering techniques or high-temperature solution methods, which increase manufacturing cost and complexity. Here, we report on a room-temperature solution process to fabricate electrochromic films of niobium oxide glass (NbOx) and ‘nanocrystal-in-glass’ composites (that is, tin-doped indium oxide (ITO) nanocrystals embedded in NbOx glass) via acid-catalysed condensation of polyniobate clusters. A combination of X-ray scattering and spectroscopic characterization with complementary simulations reveals that this strategy leads to a unique one-dimensional chain-like NbOx structure, which significantly enhances the electrochromic performance, compared to a typical three-dimensional NbOx network obtained from conventional high-temperature thermal processing. In addition, we show how self-assembled ITO-in-NbOx composite films can be successfully integrated into high-performance flexible electrochromic devices.

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Figure 1: Chemical condensation of polyniobate cluster (POM) films.
Figure 2: Compositional and structural analysis of chemically condensed (cc) NbOx films.
Figure 3: Characterization of local structure.
Figure 4: Spectroelectrochemical measurements for chemical-condensed films and devices.


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This work was carried out at the University of Texas at Austin and the Molecular Foundry, Lawrence Berkeley National Laboratory, a user facility supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231. This research was supported by a US Department of Energy ARPA-E grant. D.J.M. and G.H. acknowledge support of the Welch Foundation (F-1848 and F-1841, respectively). PDF measurements were performed at beamline ID15B of the European Synchrotron Radiation Facility (ESRF), Grenoble, France. GIWAXS data was acquired at beamline 11–3 of the Stanford Synchrotron Radiation Lightsource (SSRL). We thank D. Van Campen and C. Miller for assistance at SSRL. We also thank B. Koo for providing some of the ITO and CeO2 nanocrystals, as well as G. Garcia and J. Rivest for helpful discussions.

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A.L. and Y.W. contributed equally to this work. A.L., Y.W. and T.L. synthesized the materials, carried out the experiments, and analysed the data. P.X. and G.H. performed the DFT simulations. A.F.-M. and A.P. conducted the PDF measurements, data analysis, and interpretation. O.Z. and C.S.C. conducted the EIS and the Raman measurements, respectively. A.L., Y.W. and D.J.M. were responsible for experimental design and wrote the manuscript, which incorporates critical input from all authors.

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Correspondence to Anna Llordés or Delia J. Milliron.

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Competing interests

D.J.M. has a financial interest in Heliotrope Technologies, a company pursuing commercial development of electrochromic devices.

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Llordés, A., Wang, Y., Fernandez-Martinez, A. et al. Linear topology in amorphous metal oxide electrochromic networks obtained via low-temperature solution processing. Nature Mater 15, 1267–1273 (2016).

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