Catalyst-Free Growth of Zinc Oxide Nanorod Arrays on Sputtered Aluminum-Doped Zinc Oxide for Photovoltaic Applications

Incorporating tailored nanostructures into solar cells is a promising way to improve their photovoltaic conversion efficiency. For such solar cells, sputtered indium-doped tin oxide on glass is the standard substrate. As the global resources of indium are very limited, there is the challenge to move to other substrates and thus to synthesize nanostructures on these. We report on the growth and characterization of zinc oxide nanorod arrays on indium-free transparent conducting oxide substrates, in particular on sputtered aluminum-doped ZnO. We present a catalyst-free vapor-transport growth method at 510 degrees C, which allows for the growth of highly crystalline, well-aligned ZnO nanorods arrays with a tunable length, ranging from hundreds of nanometers to several micrometers. The nanorods exhibit an excellent crystal quality, as shown by photoluminescence measurements and high-resolution transmission electron microscopy. Optical transmission spectra show a sufficient transparency of the substrates, qualifying them for photovoltaic or optoelectronic applications. First solid-state dye-sensitized solar cells were built using nanorod arrays sensitized with a ruthenium-based dye and infiltrated with an organic hole conductor.