Phase Modulation Induced by a Photoelectric Field in Liquid Crystal Cells with Dye-Sensitized Titania Layers

In this study, we found that a photoelectric field in nematic liquid crystal (LC) cells that contains dye-sensitized titania (TiO2) layers leads to phase modulation of the LCs. When light is injected into the device, the Ru-dye is excited and electron-hole pairs are generated. The excited electrons then are transited to the conduction band of the TiO2 and transported to the ITO electrode. The holes are transported to the opposite electrode, passing through the LCs and hole-transporting layers. This charge separation by the diffusion process induces a photoelectric field across the LC cells. The birefringence of the LCs was investigated using transmission ellipsometric methods in the absence of external applied voltage. In addition, the electro-optic properties with and without the photoelectric field were compared in twisted nematic LC cells. Furthermore, optically addressed spatial light modulation by the photoelectric field was confirmed using real-time optical images.