Liquid Crystal Nanocomposites for Possible Photovoltaic Applications: Structural and Electronic Properties

Luz Martinez-Miranda (University of Maryland)

Organic photovoltaic cells are studied because of their ease of fabrication and relatively low price. Liquid crystals exhibit molecular orientation in their ordered phases (the smectic and the nematic). Alignment of the liquid crystal such that the delocalized electrons are parallel to the substrate provides a path for electrons, and holes, to move between and to reach the electrodes. Nanoparticles incorporated in a liquid crystal tend to align in rows in the liquid crystal. Together they form a heterojunction whose properties can be varied according to the nanoparticle size and shape, and the type of liquid crystal used. We have observed the role that order plays in the transfer of charges in the smectic 8CB - ZnO nanoparticle or nanorod/nanocomposite by studying the system's current-voltage (IV) curve. We investigate the role of order in the transfer of charges in the smectic 8CB - ZnO nanorod nanocomposite for nanorods 7x5x5nm3 or 12x5x5nm3 in size, and find it is larger than for the 5nm nanoparticle by at least an order of magnitude, and increases up to a concentration of 35% wt of ZnO. This is accompanied with an increase in the ordering of the liquid crystal, as observed in the analysis of the X-ray scans. Nanowires combined with liquid crystals have the same effect while providing more support to the structure. A polymeric liquid crystal has the same effect in offering more support to the nanoparticles. The enhanced ordering of the liquid crystals can contribute to the increase in the efficiency of solar cells made up of organic materials.

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