Near-infrared reflecting/transmitting smart windows based on chiral nematic liquid crystals with enhanced electrically switching performance.

Abstract

This paper addresses global warming concerns stemming from energy consumption, particularly in buildings, which contribute 40% to global energy use. Smart windows that reflect near-infrared radiation have emerged as a solution to reduce indoor temperatures. Chiral nematic liquid crystals (CLCs) play a crucial role in this technology. Numerous approaches have been explored for regulating indoor temperatures using liquid crystals. Despite achieving ideal transparency, rapid switching speeds, negligible power consumption, and user control over switching, reported samples often face challenges when attempting to revert from either the focal conic state or the transmitting state back to the initial reflecting state. In this work, for the first time to our knowledge, CLC cells with electrical reversibility are visually demonstrated rapidly switching between reflective and transmitting modes. Cell thickness emerged as a pivotal factor in achieving smart window reversibility, with 3µm identified as the optimal choice. Samples exhibited effective IR reflection, high visible transparency, and complete reversibility, marking a significant step toward practical smart windows to combat global warming.