Performance Evaluation of ‘Battery-Like’ and Hybrid Electrochromic Devices for Dynamic Solar Control in Buildings

This study evaluated the optical and electrochemical properties of tungsten oxide Electrochromic (EC) layers prepared by evaporation and electrodeposition. Minor differences in transparency were observed in the visible part of the solar spectrum. However, evaporated WO₃ films exhibited a charge capacity of 43.75 mC/cm² and a higher bias potential for complete bleaching (approximately 750 mV versus Ag/AgCl). This is in contrast to electrodeposited films, which exhibited a charge capacity of 24.87 mC/cm² and a bias potential of less than 250 mV versus Ag/AgCl. These differences in charge capacity and bias potential are due to the different film morphologies. Film thickness and porosity affect the number of coloration sites and the number of Li⁺ ions intercalated into the WO₃ film. Then, "battery-like" and hybrid Electrochromic Devices (h-ECDs) were prepared, achieving a Coloration Efficiency (CE) of up to 52 cm²/C and a contrast ratio of up to 15:1, depending on the device type and EC layer deposition method. Improved open circuit memory was achieved with "battery-like" devices irrespective of the EC layer deposition method. However, hybrid ECDs exhibited lower operating voltages and a lower bleaching capability under short circuit conditions. Thus, h-ECDs consume less energy to change color and are promising alternatives to "battery-like" devices for the dynamic control of incoming solar radiation in buildings.