The limited optical contrast and band adjustment range are the main factors that restrict chromic materials. In this study, Li+/Al3+ composite solid electrolyte is incorporated between VO2 and WO3 chromic functional layers to construct a new type of VO2 based electrothermal dual responsive devices. The dual responsive devices deliver optical contrast over 50% and independent modulation of visible and near infrared band. In addition to displaying four reversible optical states in response to environmental temperature and external voltage, the devices effectively utilize the synergistic effect of Li+/Al3+ hybrid ions. Furthermore, the optimized Li+/Al3+ composite electrolyte is proved to effectively control phase transition of VO2 and significantly improve the electrochromic properties of WO3 as well. Finally, the electro‐thermal dual responsive devices show excellent service stability in simulated outdoor environment of over 10 000 cycles. Combined with the above advantages, it is expected to develop smart windows and derivative products with large size, long life, remarkable energy saving effect and pleasant comfort.
Flexible vanadium dioxide (VO 2 ) thermochromic films show great potential for large-scale fabrication and possess broader applications compared with VO 2 coatings on rigid substrates. However, the fabrication of flexible VO 2 films remains a challenge so far, leading to the scarcity of research on flexible VO 2 films for smart windows. With the aim to obtain a flexible VO 2based films with excellent optical properties and a long service life, we designed and successfully fabricated a flexible ITO/VO 2 /ITO (IVI) film on the colorless transparent polyimide substrate, which could be directly attached to glasses for indoor temperature modulation. This flexible IVI film effectively enhances the luminous transmittance (T lum ) and solar modulation ability (ΔT sol ) (15 and 68% increase relative to a VO 2 single layer), reduces the thermal emissivity (ε T ) (50.7% decrease relative to a VO 2 single layer), and exhibits better durability than previously reported structures. Such excellent comprehensive performance offers it great potential in practical applications on smart windows. This work is supposed to provide a new strategy for facile direct fabrication of flexible VO 2 films and broaden the applications of flexible VO 2 in more coatings and devices.
VO2 is a very promising material due to its semiconductor-metal phase transition, however, the research on fs laser-induced phase transition is still very controversial, which greatly limits its development in ultrafast optics. In this work, the fs laser-induced changes in the optical properties of VO2 films were studied with a variable-temperature Z-scan. At room temperature, VO2 consistently maintained nonlinear absorption properties at laser repetition frequencies below 10 kHz while laser-induced phase transition properties appeared at higher repetition frequencies. It was found by temperature variation experiments at 100 kHz that the modulation depth of the laser-induced VO2 phase transition was consistent with that of the ambient temperature-induced phase transition, which was increased linearly with thickness, further confirming that the phase transition was caused by the accumulation of thermal effects of a high-repetition-frequency laser. The phase transition process is reversible and causes substantial changes in optical properties of the film, which holds significant promise for all-optical switches and related applications.
Building energy consumption for heating and cooling is a critical issue that has garnered wide attention due to its significant impact on global warming and sustainability. In particular, windows account for >20% of building energy loss. There is an urgent need for the independent optimization of thermal radiative properties of windows for tri-band radiation, including visible, near-infrared (NIR), and mid-infrared (MIR). Here we develop a new electrochromic structure for thermal management of windows, which is able to maximize the utilization of both solar radiation of visible and NIR light and radiative cooling of MIR light. We propose a tri-stable electrochromic device (ECD) based on the phase transitions of VO2 and WO3 films. The VO2-WO3 based ECD could realize three different optical states to independently regulate visible and NIR transmittance. Due to the decoupled barrier for opaque state in rutile LixVO2, our device also maintains non-volatility and tri-stability (<10% bleaching over 4 hours). Moreover, we introduce a new approach for thermal regulation by optimizing the emissivity of outside (εMIR-O of 0.79) and inside (εMIR-I of 0.33) electrodes to minimize radiative heat exchange between the indoor and outdoor environments. Outside experiments were performed in Sanya, China, realizing continuous all-day cooling of ~2-8 °C compared to low-e windows on a typical clear sunny day at Southern China latitudes. Simulation shows that this new ECD exhibits a higher heating and cooling energy savings than a commercial low-E glass in most climates around the world. Our findings render great opportunities for the innovative energy-saving window designs that can help achieve global carbon neutrality and sustainability.
Metal-to-insulator transition (MIT) of vanadium dioxide (VO2) has been widely researched. However, the high phase transition temperature (PTT) and single thermal phase transition severely limit its application. Hereby, the dynamic...
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