Light Absorption in Semiconductor Nanowire Arrays with Multijunction Cell Structures

Abstract

The light absorption of various types of semiconductor nanowire (NW) arrays for photovoltaic applications was calculated. The electromagnetic field in multilayer structures containing NW arrays was calculated by the scattering-matrix treatment developed by Whittaker and Culshaw [Phys. Rev. B 60 (1999) 2610], and the absorptance spectra A(λ) of the NW arrays were obtained from the transmittance and reflectivity of the structures. The ultimate efficiency η and weighted average absorptance Aavr of the NW array solar cells were evaluated from A(λ). A general tendency of the light absorption in NW arrays in relation to their structural parameters, such as the pitch a of an NW array and the size d of an NW, was identified, and the differences between the optimum structural parameters of NW arrays in terms of light absorption in the cases of InP, GaAs, Si, and Ge were determined. The maximum η was obtained for a= 375, 350, 700, and 400 nm, for InP, GaAs, Si, and Ge NW arrays with d/a=0.5, respectively. Moreover, Aavr for multijunction structures consisting of GaAs and Ge NWs and GaAs NWs on a germaninum substrate was also calculated and showed that both of these structures exhibited good light trapping capabilities for photovoltaic applications. It is shown that the photogeneration profiles of carriers in two types of multijunction structures are different.