A concept for switchable, energy-generating ‘smart’ windows

Smart’ windows, mostly based on chromogenic events triggered chemically, electrically or otherwise, are able to variably control the amount of light that passes into a room space, but make no use of the rejected light. Photovoltaic ‘windows’ such as those based on thin films or tiled photovoltaic cells, on the other hand, may used absorbed light to generate electricity, but are incapable of adjusting transparency. I propose to use fluorescent dye guests in a liquid crystal host sandwiched between glass panels as a new type of ‘smart’ window. The dye material absorbs a variable amount of light depending on its orientation, which may be altered at will by aligning the liquid crystal host through application of an electric field. The absorbed light, rather than being lost, is re-emitted by the fluorescent molecules. A significant fraction of this light becomes trapped in the glass window panels by total internal reflection, and becomes concentrated along the edges of the device. To the edges of the glass waveguides may be attached small photovoltaic cells for generation of electricity. In this work I discuss preliminary results on model ‘smart’ window systems. I demonstrate that there is a variation of absorption upon adjusting the voltage applied to the cell. While there is a concurrent decrease in the amount of light emitted from the edge as the transmission of the window is increased, the variation in edge output is less than the variation in transmission, due to enhanced efficiency of light transport as the dye molecules alter their alignments.