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.

Photo-induced vacancy defects are employed strategically to imbue semiconductors with enhanced performance characteristics for many important applications such as surface-enhanced Raman scattering (SERS) sensing, photocatalysis, and photovoltaic applications. However, the long-term maintenance and use of photo-induced vacancy defects remain elusive, because of their rapid self-healing upon air exposure. In this study, we demonstrate that photo-induced oxygen vacancy (PIV_O) defects can be stabilized by the photoexcitation of metal–organic framework (MOF) materials, which is crucial for SERS analysis. The PIV_O defects in MOF materials are stable for at least two weeks in the ambient atmosphere, owing to the combination of steric hindrance and electron delocalization around vacancy defects, which significantly contrasts the short lifetime (within minutes) of PIV_O defects in metal-oxide semiconductors. With the formation of stable PIV_O defects, a prominent SERS enhancement surpassing that of pristine MOFs is achieved, accompanied with a reduced limit of detection by three orders of magnitude. Moreover, the additional SERS enhancement rendered by PIV_O defects can be stably retained and is effective for monitoring various small molecules, such as dopamine and bisphenol A.