A multicolor electrochromic device with on-demand solar thermal management for smart building envelopes

Buildings account for over 30% of global energy consumption, about half of which is used for heating, cooling, and ventilation to regulate indoor temperatures. With the energy crisis looming, saving energy from thermal regulation in buildings will make a significant contribution to sustainable development. Windows and walls are major enveloping parts of buildings, responsible for regulating light and heat indoors from the sun. However, compared to the well-studied smart windows, research on smart building envelopes is still lacking. Herein, we demonstrate a reflective-type dual-function electrochromic (DFEC) device for building envelopes, capable of producing rich color variations in the visible (VIS) and achieving large average reflectivity modulation of over 80% in the near infrared (NIR). Due to the inherent energy recyclability of EC batteries, the DFEC devices reveal ultra-low energy consumption of 30.7 mWh/m² and power consumption of 0.4 mW/cm² in single EC cycle. As a demonstration, the DFEC device exhibits a remarkable performance in solar thermal management with a temperature difference of 5 °C between its colored (heating) and bleached (cooling) states, indicating an extensive potential for application in energy-efficient building envelopes.