An embodiment of nanostructure includes a conductive substrate; an insulating layer on the conductive substrate, metal nanoparticles, and elongated single crystal nanostructures. The insulating layer includes an array of pore channels. The metal nanoparticles are located at bottoms of the pore channels. The elongated single crystal nanostructures contact the metal nanoparticles and extend out of the pore channels. An embodiment of a photovoltaic device includes the nanostructure and a photoabsorption layer. An embodiment of a method of fabricating a nanostructure includes forming an insulating layer on a conductive substrate. The insulating layer has pore channels arranged in an array. Metal nanoparticles are formed in the pore channels. The metal nanoparticles conductively couple to the conductive layer. Elongated single crystal nanostructures are formed in the pore channels. A portion of the insulating layer is etched away, which leaves the elongated single crystal nanostructures extending out of the insulating layer.
STATEMENT OF GOVERNMENT SUPPORT
 This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in this invention.