Rational geometrical design of multi-diameter nanopillars for efficient light harvesting

Three-dimensional arrays of nanostructures have drawn increasing attention for solar energy harvesting in recent years. In this work, with Ge as the model material, the broadband solar spectrum absorption of arrays of multi-diameter nanopillars is explored with finite difference time domain simulations. It is found that light absorption of a nanopillar array is either determined by the material filling ratio or by transverse resonance leaky modes depending on input wavelength. A properly designed multi-diameter nanopillar array can compete with a nanocone array on broadband light absorption capability. As single crystalline multi-diameter nanopillars can be grown with a bottom-up approach, the investigation here provides important design guidelines for the fabrication of efficient nanostructured photovoltaic and other optoelectronic devices. (C) 2013 Elsevier Ltd. All rights reserved.