Sol-gel-based porous Ti-doped tungsten oxide films for high-performance dual-band electrochromic smart windows

The dual-band electrochromic smart window is based on sol-gel porous film featuring simultaneously a large optical modulation, high coloration efficiency, fast response, excellent bistability, and good cycle stability. • A facile and effective sol-gel strategy using a foaming agent to achieve porous Ti-doped tungsten oxide film for dual-band electrochromic smart windows is demonstrated for the first time. • The sol-gel film delivers impressive high-performance independent control of the transmittance of near-infrared and visible light. • The devices based on sol-gel film support selectively and independently regulate light and heat in sunlight. Dual-band electrochromic smart windows (DESWs) with independent control of the transmittance of near-infrared and visible light show great potential in the application of smart and energy-saving buildings. The current strategy for building DESWs is to screen materials for composite or prepare plasmonic nanocrystal films. These rigorous preparation processes seriously limit the further development of DESWs. Herein, we report a facile and effective sol-gel strategy using a foaming agent to achieve porous Ti-doped tungsten oxide film for the high performance of DESWs. The introduction of foaming agent polyvinylpyrrolidone during the film preparation can increase the specific surface area and free carrier concentration of the films and enhance their independent regulation ability of near-infrared electrochromism. As a result, the optimal film shows excellent dual-band electrochromic properties, including high optical modulation (84.9% at 633 nm and 90.3% at 1200 nm), high coloration efficiency (114.9 cm 2 C -1 at 633 nm and 420.3 cm 2 C -1 at 1200 nm), quick switching time, excellent bistability, and good cycle stability (the transmittance modulation losses at 633 and 1200 nm were 11% and 3.5% respectively after 1000 cycles). A demonstrated DESW fabricated by the sol-gel film showed effective management of heat and light of sunlight. This study represents a significant advance in the preparation of dual-band electrochromic films, which will shed new light on advancing electrochromic technology for future energy-saving smart buildings.