Liquid-crystal–electrochromic-material interface: A p-n-like electro-optic junction

A liquid crystal (LC) cell has been made by using a standard sandwich configuration with one of the indium tin oxide (ITO) electrodes covered by a thin layer of tungsten trioxide (WO₃). In this kind of cell optical polarization switching (observed under a crossed polarizer microscope) occurs for only one of the two polarities of an ac external applied electric field, while in the usual liquid crystal cells the electro-optic response does not depend on the sign of the field. The inhibiting switching configuration corresponds to anodic polarization of the tungsten trioxide film in which the deintercalation of cations occurs. Here we present the time behavior of charge and discharge for both the anodic and cathodic currents. A model based on charge carrier exchange between the ITO-WO₃ and WO₃-LC interfaces and also electrochemical processes is reported. Our model is also capable of explaining the electric and electro-optic asymmetric responses of the cell. Numerical calculations confirm the model.