Solvothermally-synthesized tin-doped indium oxide plasmonic nanocrystals spray-deposited onto glass as near-infrared electrochromic films

Nanocrystals of semiconducting, highly-doped metal oxides present localized surface plasmon resonance properties responsible for intense optical absorption in the near-infrared (NIR) spectral range. These features make them strong candidates for designing “new generation”, spectrally-selective electrochromic smart windows and other optoelectronic devices. In the present study, nanocrystals of tin-doped indium oxide (ITO) are solvothermally-synthesized in benzyl alcohol. Their structure, morphology and composition are assessed by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, while their optical plasmonic behavior is evidenced by means of VIS-NIR spectrometry and electron energy loss spectroscopy coupled to scanning transmission electron microscopy. Remarkably, the latter setup allows for the value-added acquisition of high-resolution mappings and quantifications of the nanocrystals individual plasmon responses at both surface and bulk levels. Inks of ITO nanocrysals are then spray-coated onto glass to act as NIR-modulating plasmonic electrochromic layers. ITO dispersions are straightforwardly deposited from low toxic media (isopropanol) according to a room-temperature procedure implying no harsh chemical or thermal post-treatment – only a mild drying step at 100 °C for 10 min. Finally, in situ spectroelectrochemical measurements completed on the films immersed in liquid electrolyte show appreciable NIR contrasts (up to 40%) upon electrochemical charge/discharge, together with a >80% VIS transmittance.