RESUMEN
This study theoretically proved that although reciprocal optical devices can show asymmetric transmittivity (AT) under controlled incident modes (i.e., conditional AT), they cannot guarantee AT with arbitrary incident light modes, whereas only nonreciprocal optical devices can possibly guarantee AT. Besides, the thermodynamics of both reciprocal and nonreciprocal optical devices were discussed to show that the second law of thermodynamics is valid anyway. Furthermore, the diode-like behaviors of optical and electronic devices were compared. Electrons are identical to electronic devices, so electronic devices could have asymmetric conductance regardless of electrons. In contrast, electromagnetic waves are different from optical devices as transmittivity of different modes can be different, so reciprocal optical devices showing conditional AT cannot guarantee AT when incident modes are arbitrary. The mathematical proof and characteristic comparisons between electronic and optical diodes, which are firstly presented here, should help clarifying the necessary nonreciprocity required for being optical diodes.
RESUMEN
Uncontrolled sunlight entering through windows contributes to substantial heating and cooling demands in buildings, which leads to high energy consumption from the buildings. Recently, perovskite smart windows have emerged as innovative energy-saving technologies, offering the potential to adaptively control indoor solar heat gain through their impressive sunlight modulation capabilities. Moreover, harnessing the high-efficiency photovoltaic properties of perovskite materials, these windows have the potential to generate power, thereby realizing more advanced windows with combined light modulation and energy harvesting capabilities. This review summarizes the recent advancements in various chromic perovskite materials for achieving light modulation, focusing on both perovskite structures and underlying switching mechanisms. The discussion also encompasses device engineering strategies for smart windows, including the improvement of their optical and transition performance, durability, combination with electricity generation, and the evaluation of their energy-saving performance in building applications. Furthermore, the challenges and opportunities associated with perovskite smart windows are explicated, aimed at stimulating more academic research and advancing their pragmatic implementation for building energy efficiency and sustainability.
RESUMEN
A wearable textile that is engineered to reflect incoming sunlight and allow the transmission of mid-infrared radiation simultaneously would have a great impact on the human body's thermal regulation in an outdoor environment. However, developing such a textile is a tough challenge. Using nanoparticle-doped polymer (zinc oxide and polyethylene) materials and electrospinning technology, we have developed a nanofabric with the desired optical properties and good applicability. The nanofabric offers a cool fibrous structure with outstanding solar reflectivity (91%) and mid-infrared transmissivity (81%). In an outdoor field test under exposure of direct sunlight, the nanofabric was demonstrated to reduce the simulated skin temperature by 9 °C when compared to skin covered by a cotton textile. A heat-transfer model is also established to numerically assess the cooling performance of the nanofabric as a function of various climate factors, including solar intensity, ambient air temperature, atmospheric emission, wind speed, and parasitic heat loss rate. The results indicate that the nanofabric can completely release the human body from unwanted heat stress in most conditions, providing an additional cooling effect as well as demonstrating worldwide feasibility. Even in some extreme conditions, the nanofabric can also reduce the human body's cooling demand compared with traditional cotton textile, proving this material as a feasible solution for better thermoregulation of the human body. The facile fabrication of such textiles paves the way for the mass adoption of energy-free personal cooling technology in daily life, which meets the growing demand for healthcare, climate change, and sustainability.
