A facile synthesis of porous amorphous/crystalline TiO2 hybrids for enhanced electrochromic performances

Abstract

Porous crystalline/amorphous TiO2 (c/a-TiO2) hybrid films have been successfully grown on FTO substrates via a solvothermal reaction followed by a simple air annealing treatment. By adjusting reaction temperature, the porous structure and the proportion of amorphous TiO2 phase can be feasibly modulated. The in-situ transformation of crystalline TiO2 from amorphous phase could ensure the optimal crystalline/amorphous interface contact. The obtained c/a-TiO2 hybrid films shows excellent electrochromic properties which can switch between green color and transparent state with large optical contrast (59.3%) at 700 nm, high coloration efficiency (24.3 cm2 C−1) and short switching time (bleaching time of 2.0 s and coloration time of 12.1 s). Due to the desired porous structure for short Li+ ions diffusion paths and crystalline/amorphous interface enables low energy barrier and fast ion migration during the insertion/extraction of Li+ ions, the c/a-TiO2 hybrid film not only exhibits lower threshold voltage (+0.2 ∼ −1.5 V vs Ag/AgCl) and faster response than single crystalline anatase TiO2 (c-TiO2) counterpart, but also owns higher coloration efficiency and better durability than single amorphous TiO2 (a-TiO2). Compared to the commonly blue color of c-TiO2, the success to gain green color by using the prepared c/a-TiO2 hybrid film makes it very attractive for constructing electrochromic devices. Our study here also offers an alternative way of designing TiO2-based nanostructures for high-efficiency electrochromic applications.