Low-Electric-Field-Driven Smart Window Enabled by Poly(vinyl chloride) Gel with Carbon Nanotube Transparent Electrodes

Among various kinds of active transparency-tunable smart windows, voltage-controlled surface microroughness in transparent elastomer membranes attracts extensive attention due to its compactness, low cost, large tuning range, etc. However, this kind of smart window device usually features high driving voltage (thousands of volts), slow response, and unstable performance. Herein, a low-electric-field-driven transparency-tunable smart window is proposed based on voltage-induced roughness variation in electroactive poly(vinyl chloride) (PVC) gel actuators. Highly conductive mesh-like single-walled carbon nanotube (CNT) transparent film and highly transparent indium tin oxide glass are used as the PVC gel actuator’s anode and cathode, respectively. The surface micromorphology of a CNT–PVC gel interface shows drastic roughness variation by applying an external voltage, thereby enabling the transparency change of the PVC gel-based smart window. The proposed transparency-tunable window achieves an exceptional in-line transmittance tuning range of 18–67% under an ultralow driving electric field of 2 V/μm. The operational voltages are significantly lower than those of other reported transparency-tunable windows operating on the same principle (tens of volts per micron). Moreover, the proposed smart window device demonstrates excellent haze retention property, good humidity resistance (30–90%), and outstanding cyclic stability (10000 cycles). The response time is evaluated visually and is less than 1 s under a 400 V applied voltage, which demonstrates near-instantaneous switching capabilities suitable for both smart windows and dynamic displays. Finally, the potential application of the device is further explored by fabricating a refreshable 7-segment display that dynamically switches between Arabic numerals in real time.