Solar power conversion efficiency in modulated silicon nanowire photonic crystals

It is suggested that using only 1 mu m of silicon, sculpted in the form of a modulated nanowire photonic crystal, solar power conversion efficiency in the range of 15%-20% can be achieved. Choosing a specific modulation profile provides antireflection, light trapping, and back-reflection over broad angles in targeted spectral regions for high efficiency power conversion without solar tracking. Solving both Maxwell's equations in the 3D photonic crystal and the semiconductor drift-diffusion equations in each nanowire, we identify optimal junction and contact geometries and study the influence of the nanowire surface curvature on solar cell efficiency. We demonstrate that suitably modulated nanowires enable 20% efficiency improvement over their straight counterparts made of an equivalent amount of silicon. We also discuss the efficiency of a tandem amorphous and crystalline silicon nanowire photonic crystal solar cell. Opportunities for hot carrier collection and up-conversion of infrared light, enhanced by photonic crystal geometry, facilitate further improvements in power efficiency. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752776]