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 (NbO_x) and 'nanocrystal-in-glass' composites (that is, tin-doped indium oxide (ITO) nanocrystals embedded in NbO_x 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 NbO_x structure, which significantly enhances the electrochromic performance, compared to a typical three-dimensional NbO_x network obtained from conventional high-temperature thermal processing. In addition, we show how self-assembled ITO-in-NbO_x composite films can be successfully integrated into high-performance flexible electrochromic devices.