Path length enhancement in disordered media for increased absorption
Résumé
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.