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. Electrochromic films based on tin-doped indium oxide nanocrystals dispersed in a niobium oxide glass are now realized from solution at room temperature. The chain-like topology of niobium oxide improves the electrochemical properties of these films.