Elimination of grayscale viewing angle asymmetry in guest-host liquid crystal smart windows via surface-protrusion-induced random planar alignment

초록

Guest-host liquid crystal (GHLC) smart windows have attracted significant interest for their ability to regulate solar radiation through angular-selective absorption. While conventional vertically aligned (VA) GHLC cells effectively block oblique light while maintaining a clear normal view, they encounter severe viewing angle asymmetry when modulating grayscale levels. This distortion arises because the application of a vertical electric field causes the liquid crystal (LC) directors and dichroic dyes to tilt in a specific azimuthal direction, shifting the transmittance peak away from the normal axis. In this study, we propose a protrusion-induced random planar alignment (RPA) structure to eliminate this grayscale asymmetry. By incorporating a periodic array of cylindrical surface protrusions, we induce a multi-domain LC orientation that statistically averages the azimuthal absorption profiles. Full 3D optical simulations using the Berreman matrix method demonstrate that while a single-domain VA cell exhibits an asymmetric "crescent-shaped" transmittance contour during grayscale switching, the proposed RPA cell provides perfectly symmetrical viewing angle characteristics across all intensity levels. The device achieves a low driving voltage of approximately 8 V and maintains haze-free analog switching, offering a robust and high-quality solution for advanced architectural and automotive smart glazing applications.

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