Aggregate particles comprising titanium dioxide (TiO.sub.2) nanotubes, methods for making the aggregate particles, photoelectrodes for solar cells including aggregate particles of nanomaterials, methods for making the photoelectrodes, and solar cells that include the photoelectrodes.
STATEMENT OF GOVERNMENT LICENSE RIGHTS
 This invention was made with Government support under Grant No. DE-FG02-07ER46467 awarded by United States Department of Energy and under Grant No. FA9550-06-1-0326 awarded by the Air Force Office of Scientific Research. The Government has certain rights in the invention.