Bifunctional solid state electrochromic device using WO3/WS2 nanoflakes for charge storage and dual-band color modulation

Abstract

A new methodology to enhance electrochromic performance and make it multifunctional ready has been demonstrated where an all-organic solid state electrochromic device has been made to display dual band color switching in the visible and near-infrared (NIR) spectrum. Additionally, energy storage capabilities have been added to make it a multifunctional solid-state device. A mixture of WS₂/WO₃ synthesized by the hydrothermal technique was characterized by X-ray diffraction, scanning electron microscopy (SEM), and Raman microscopy, prior to being used as a dopant with polythiophene (P3HT) and ethyl viologen (EV) active electrochromic layers. In situ kinematics was performed to check the electrochromic performance of the device in two wavelength (visible ∼515 nm and NIR ∼800 nm) regions. The fabricated device shows improved electrochromic performance in terms of switching time, color contrast, efficiency, and stability/cyclability in both wavelength regions of the electromagnetic spectrum. A very small external voltage bias (±1.5 V) was enough to switch the device (magenta ↔ blue) very quickly by taking less than a second's time. Furthermore, the supercapacitive performance parameters of the device have been investigated through cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) curves, and electrochemical impedance spectroscopy (EIS). The results show that the specific capacitance value of the device is ∼50 F g⁻¹ at a current density of 1 A g⁻¹ along with a fast response (charging/discharging) time and excellent energy density. The designed electrochromic supercapacitor device successfully demonstrated excellent capacitive performance along with ability as an electrochromic indicator and paves the way for the integration of electrochromic energy storage indicators in various energy storage or energy-efficient buildings.