Growth of Ordered Nanostructure Arrays including Nanotubes and Nanorods for High Efficiency Solar Cells

Research and development in the field of high efficiency solar energy conversion relies heavily on the fabrication of the photoabsorber materials as nanotubular or nanowire architectures, since these morphologies gives better photocurrent output with lese coverage of the active material. However, fabrication of the nanostructured semiconducting materials as vertically aligned, highly ordered nanowire or nanotubular arrays with precise distribution of size and shape over the entire region of interest is still a significant challenge to overcome. In this presentation, we will describe a straightforward approach for the fabrication of CdTe nanorod and nanotube arrays with a high degree of precision through confined electrodeposition on lithographically patterned nanoelectrodes. This technique has the potential of growing these nanotube/nanowire arrays over a significantly large area that can be scaled up to the industrial manufacturing scale. The desired nanoelectrode pattern was defined through electron beam lithography on indium tin oxide coated glass, which was used as a typical conducting substrate, and electrodeposition of the semiconducting material of interest (CdTe) on the nanoelecrodes was used to grow the nanotubes/nanowires. Nanosphere Photo Lithography technique was used to define nanorod/nanowire patterns over a significantly larger area (4 x 4 cm²). It is interesting to note that the measured photocurrent density of nanotube device created by this protocol exceeds that obtained from a thin film device fabricated under similar conditions by several orders of magnitude. The ability to tune the entire nanotube/nanorod diameter, length, shape, packing density, and nanotube wall thickness, make this method a versatile tool to fabricate and investigate the nano-structured photovoltaic devices and study their structure-property relationship. Additionally the ability to create uniform nanotube/nanorod arrays through one-step electrodeposition makes this protocol unique. The simplicity of this method opens up a window of opportunities to investigate the effect of morphology on the solar cell efficiency of different semiconducting materials. In this presentation we will discuss the growth of nanorod and nanotube arrays through patterned electrodeposition on nanoelectrodes, and discuss detailed investigation of their characterization and solar cell efficiencies along with future prospects for tuning the efficiencies even further.