Path length enhancement in disordered media for increased absorption

TL;DR

This paper investigates how disordered media can enhance optical path lengths and light absorption in dielectric slabs through scattering, revealing optimal scattering conditions for maximum absorption enhancement.

Contribution

It provides a combined theoretical and numerical analysis of path length enhancement in disordered media, including analytical expressions and insights into optimal scattering regimes.

Findings

Long optical paths can occur with minimal scattering due to total internal reflection.

Maximum absorption enhancement occurs at an intermediate scattering strength.

The results can inform more efficient photovoltaic device designs.

Abstract

We theoretically and numerically investigate the capability of disordered media to enhance the optical path length in dielectric slabs and augment their light absorption efficiency due to scattering. We first perform a series of Monte Carlo simulations of random walks to determine the path length distribution in weakly to strongly (single to multiple) scattering, non-absorbing dielectric slabs under normally incident light and derive analytical expressions for the path length enhancement in these two limits. Quite interestingly, while multiple scattering is expected to produce long optical paths, we find that media containing a vanishingly small amount of scatterers can still provide high path length enhancements due to the very long trajectories sustained by total internal reflection at the slab interfaces. The path length distributions are then used to calculate the light absorption efficiency of media with varying absorption coefficients. We find that maximum absorption enhancement is obtained at an optimal scattering strength, in-between the single-scattering and the diffusive (strong multiple-scattering) regimes. This study can guide experimentalists towards more efficient and potentially low-cost solutions in photovoltaic technologies.