Niobium and Fluorine Dually Doped Titanium Oxide Nanosheet Arrays for Selective Dual-Band Electrochromic Applications

Abstract

Dual-band electrochromic (EC) films selectively modulating visible (VIS) and near-infrared (NIR) light promise an attractive option for efficiently utilizing solar energy. Anatase titanium dioxide (TiO2) promises dual-band EC capability; however, it suffers from the difficulty in circumventing the obstacle in the NIR region and sluggish reaction kinetics as well as poor cycling stability. In this work, 2D (Nb, F) co-doped TiO2 nanosheets (NSs) arrays are reported as an effective single-component dual-band EC material. The co-doping can induce an oriented growth of freestanding ultrathin NSs with exposed (001) facets which promote the EC reaction kinetics. The high aspect ratio and orientation of the nanosheets favor the localized surface plasmon resonance (LSPR) effect triggered by electrochemical bias voltages, thus achieving independent modulation of the NIR transmittance. Three application scenarios of the NSs can be presented based on selective, efficient, and high optical modulation in the NIR and VIS regions (79.5% at 700 nm and 78.4% at 1300 nm, respectively), unprecedented fast bleaching/coloring times (3.0/8.4 s), and a long cycle life (500 cycles). Moreover, the films exhibit multi-color EC and energy storage materials. This work may provide an insight into the single-component dual-band EC mechanism of 2D TiO2 nanostructures and present promising potential for energy saving and smart display applications.