Energy saving, transparency changing thermochromism in dye-doped cholesteric liquid crystals for smart windows

Abstract

An electrically switchable smart window is made from a dye-doped Cholesteric liquid crystal (CLC). In this work, the impact of coumarin dye (0.3 and 1 wt%) on the structural and electro-optical properties of CLCs that reflect IR and blue light (Blue) was explored. The results suggest that high transmittance in Visible and NIR useful to preserve interior transmittance as well as heat suited for all seasons. Temperature-dependent microscopic studies confirmed the homogenous solubility of the dye in CLCs. The fabricated smart window was observed to show three switchable modes, comprising planar (P), focal-conic (FC), and homeotropic (H) states, depending on the applied voltages (1 kHz). The structural observations from microscopic studies and the transmission spectra of pure and dye-doped composites with and without the application of voltage are consistent. The visual transmittance of dye doped CLC increased from 84% in the planar state (OFF state) to 18% in the focal conic state (3 V/µm) and 92% in the homeotropic state (5 V/µm) with a short response time (<1ms). Using dye and CLCs, we demonstrated the functionality of the device as smart windows for energy saving, privacy windows as well as for authenticated/unauthenticated QR codes. To investigate the impact of both pure CLC and dye-doped CLC devices on interior temperature management, a solar simulator device was used. The findings demonstrate that the device can be used as a smart window to regulate the internal temperature throughout the year, cutting down on the expense of operating artificial lighting, heating, and cooling systems for buildings. In comparison to pure CLCs, coumarin dye-doped CLCs showed high transmittance in the transparent and homeotropic state and a low transmittance in the scattering state when an electric field is applied and it also exhibited a good stability over repeated switching cycles.