Nanowire-based Solar Cells

Excitonic solar cells – including organic, hybrid organic-inorganic and dye-sensitised cells (DSCs) – are promising devices for inexpensive, large-scale solar energy conversion. The DSC is currently the most efficient and stable excitonic photocell. Central to this device is a thick nanoparticle film that provides a large surface area for the adsorption of light-harvesting molecules. However, nanoparticle DSCs rely on trap-limited diffusion for electron transport, a slow mechanism that can limit device efficiency, especially at longer wavelengths. We have introduced a new version of the dye-sensitised cell in which the traditional nanoparticle film is replaced by a dense array of oriented, crystalline ZnO nanowires. The direct electrical pathways provided by the nanowires ensure the rapid collection of carriers generated throughout the device, and a full Sun efficiency of 3.5% has been demonstrated, limited primarily by the surface area of the nanowire array. We are now extending our synthetic strategy to design nanowire electrodes with much larger areas available for dye adsorption. It is worth noting that the advantages of the nanowire geometry are even more compelling for other types of excitonic photocells, such as inorganic-polymer, inorganic composite hybrid devices, in which an oriented, continuous and crystalline inorganic phase could greatly improve charge collection.

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