Polythiophene-nanoWO3 bilayer as an electrochromic infrared filter: a transparent heat shield

Abstract

A power-efficient, ultrafast and stable organic–inorganic hybrid electrochromic device fabricated using WO₃ and P3HT as active materials has been demonstrated herein for dual application in an electrochromic window as well as an IR filter. The device when turned ON using a bias as low as 1 V shows heat shielding effect as well as increased optical transparency to keep the area cooler by ∼8 °C (22%) to maintain the room temperature at 302 K, as imaged using an IR camera. The solid state electrochromic IR filter device was fabricated in simple cross bar geometry with the WO₃/P3HT bilayer sandwiched between two electrodes. The device works on the principle of a bias-induced redox change process, as established using electrochemical and spectroscopic investigations. The device exhibits superior electrochromic behavior with dual function, with a maximum color contrast of ∼60% in the IR region with excellent coloration efficiency of ∼380 cm² C⁻¹ at 520 nm and stability of more than 1600 ON/OFF cycles without compromising its performance. Possibility of the device to be used as an electrochromic window and heat shield has been demonstrated using real life experiments.