Environmentally friendly energy resources are needed to meet our clean energy demand. Semiconductor nanoparticle and nanotube assemblies provide new ways to develop next generation solar cells.[1-4]. Of particular interest is the
nanowire/nanotube architecture which can significantly improve the efficiency of nanostructure based solar cells. We have now developed quantum dot solar cells by assembling different size CdSe quantum dots on TiO2 films composed of particle and nanotube morphologies (Scheme 1). Upon bandgap excitation, CdSe quantum dots inject electrons into TiO2 nanoparticles and nanotubes, thus enabling the generation
of photocurrent in a photoelectrochemical solar cell. These composite semiconductor nanostructures can be tailored to tune the photoelectrochemical response via size control of CdSe quantum dots and improve the photoconversion efficiency by facilitating the charge transport through TiO2 nanotube architecture. Ways to improve power conversion efficiency and maximize the light harvesting capability through the construction of a rainbow solar cell and carbon nanotube-semiconductor hybrid assemblies will be presented. The salient features of carbon nanotube and graphene scaffolds for facilitating charge collection and charge transport will also be discussed
