Comparative optical analysis of GaAs nanostructures for photovoltaic applications using finite element method

Abstract

In this manuscript, a thorough comparative analysis of six GaAs based nanostructures (hollow and solid) is performed on the basis of their optical performance. These nanostructures are known to exhibit excellent anti-reflection properties, owing to their ability to generate a broadband absorption spectrum through efficient photon harvesting. Using the Finite Element Method (FEM) of the commercially available COMSOL Multiphysics package, the absorption characteristics, optical short circuit current density (JSC), electric field and photogeneration rates of six different nanostructures namely concentric nanocylinder (CNCy), hollow concentric nanocylinder (HCNCy), inverted nanopencil (INPe), hollow nanopencil (HNPe), nanorod + nanohemisphere (NR + NHe), and hollow nanorod + hollow nanohemisphere (HNR + HNHe) are computed. The optical performance of these nanostructures is largely dependent on their geometrical parameters such as filling ratio (FR = Diameter/Period), spacing and structural dimensions. The optimized values of these parameters can play a vital role in capturing the optical resonance modes by the nanostructures to produce absorption enhancement. It has been observed that the nanostructures with base diameter of 240 nm, period in the range of 300–350 nm and FR of 0.8 exhibit better optical characteristics. Optical JSC and optical efficiency of 29.45 mA cm−2 and 42.26%, respectively for CNCy nanostructure with FR of 0.8 and diameter of 240 nm is the highest among all the nanostructures. The effect of the angle of incidence of the photons striking the nanostructures on the average absorptance in both Transverse Electric (TE) and Transverse Magnetic (TM) modes are also investigated. In addition to this, we have also computed the effective refractive index for all the nanostructures using Maxwell Garnett formula in order to estimate the surface anti-reflection characteristics of these nanostructures.