Broadband Absorption in Thin Films Motivated by Strong Light Bending

Abstract

Photon management toward the absorption over a wide spectral range of the solar light is important to various absorption‐based photonic devices. The key for high absorption in thin films is the ability to “bend the light” from the normal direction into the in‐plane direction. Broadband absorption enhancement is reported in thin films decorated with top surface light funnel arrays (LF arrays) due to strong bending of the light by the arrays into the films, in contrast with excitation of thin films by top surface nanopillar arrays (NP arrays) that is governed by forward scattering. The broadband absorption in the film below the LF array (LF film) is 40% higher than that in a film below an optimized NP array (NP film). Also, the strong light bending by the LF arrays into the underlying film induces strong absorptivity peaks substantially exceeding the Yablonovitch limit for both the LF film and the total array–film complex. Finally, the superior LF film broadband absorption is due to strong light bending from the normal direction into the in‐plane direction which is manifested in efficient generation of mode hybridizations.

Keywords

• gratings
• light bending
• nanophotonics
• nanopillar arrays
• optical absorption
• solar energy