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

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 cm(2) 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 similar to -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.

Automated summary

Porous crystalline/amorphous TiO2 hybrid films with excellent electrochromic properties were successfully grown through a solvothermal reaction and air annealing treatment. The films exhibited large optical contrast, high coloration efficiency, and short switching time. They also showed lower threshold voltage and better durability compared to single crystalline and single amorphous TiO2 materials.