Broadband Absorption Enhancement with Silicon Light Funnel Arrays

The Yablonovitch limit for light trapping can be exceeded using arrays of subwavelength structures as these introduce additional localized trapped modes (Mie modes) and hybridization of these with other modes (i.e. e.g. guided modes in the underlying substrate). We recently introduced the paradigm of light trapping based on arrays of subwavelength silicon light funnels (LFs). In the current work, we use 3D finite-difference time-domain (FDTD) calculations to examine light trapping and broadband absorption of the solar spectrum in free-floating LF arrays as well as in LF arrays coupled with underlying substrates. We show that the broadband absorption of the solar radiation in LF arrays is superior to that of optimized nanopillar arrays. The broadband absorption in free-floating LF arrays and in LF arrays coupled with underlying substrates are characterized by strong spectral absorption peaks that can reach the Yablonovitch limit. We investigate the absorptivity dependency on the bottom diameter of the LFs. We show that a 3 µm high LF array with D_b=100 nm exhibits ultimate absorption efficiency enhancement of ~14% and ~55% relative to optimized NP array and thin film, respectively. This work describes light trapping and broadband absorption of the solar radiation in LF arrays which can potentially pave the way to thin-film photovoltaic cells and other solar energy applications.

Keywords: light funnel arrays, array of subwavelength features, light trapping, nanophotonics, broadband absorption, photovoltaic technology.