Hybrid smart window for visibility control and heat blocking utilizing NMP-LC liquid crystal tunable scattering mode with nanostructured VO2 metasurface

Abstract

A hybrid smart window is demonstrated by integrating vanadium dioxide (VO₂) nanostructured thin film (nSTF), prepared using oblique angle deposition, with a liquid crystal (LC) doped with nanoporous microparticles (NMP-LC mode). The device exhibits a non-reciprocal effect due to its asymmetric nature involving absorption and scattering layers, where the thermochromic performance is superior when the VO₂ side faces outward. Although the thermochromic properties of VO₂ are slightly reduced during device integration, the infrared (IR) blocking capability is enhanced. When the VO₂ side faces outward, the device achieves T_IR ∼ 19 % and R_IR ∼ 52 %, compared to T_IR ∼ 17 % and R_IR ∼ 41 % when the LC side faces outward. This IR blocking, achieved through reflection and absorption, mimics the effect of an insulating layer, contributing to energy savings. The LC, enriched with nanoporous microparticles, exhibits a tunable scattering effect that allows dynamic control of visible light transparency. Additionally, the VO₂ nSTF aligns the LC and functions as an electrode, lowering production costs. The optical properties of the VO₂ nSTF are modeled using the anisotropic Bruggeman formalism and the 4 × 4 matrix formalism. The transmission and reflection characteristics in the non-scattering state agree well with experimental observations for both the VO₂ nSTF and the full device. However, in the scattering state, while general trends are captured, quantitative agreement requires more rigorous scattering models. The operation voltage is found to decrease when the frequency is reduced, hence reducing the required operation power by more than an order of magnitude. The integration of the two materials, VO₂ and NMP-LC, enhances the functionality of smart windows, advancing their potential for achieving near-zero energy solutions.