Nanocolumnar ZnO films for photovoltaic applications

Zinc oxide (ZnO) is a wide gap semiconductor that if grown under nanostructured form, is suitable for photovoltaic applications as a way to enlarge the active part of a solar cell. Voids of enlarged surfaces of textured substrates can be filled with a thin absorber. The main advantage of such light-collecting devices is the short electronic transport distance needed which reduces the requirement of large diffusion lengths. Crystalline ZnO nanocolumns were obtained by electrodeposition on polycrystalline conductive glass and on monocrystalline GaN substrates. Sizes and surface–volume ratios of the ZnO columns depend mainly on the growth parameters such as current density, deposition time and temperature of the bath. The intense ultraviolet photoluminescence emission observed in ZnO columns grown under different conditions depends mainly on post-annealing treatment.