Arrays of nano-light-mixers for enhanced broadband and omnidirectional absorption of the solar radiation for solar energy technologies

Abstract

Broadband and omnidirectional absorption is the first requirement for any solar energy harvesting technology. For example, the realization of silicon thin-film photovoltaics is hampered by the low absorption coefficient of silicon. This work introduces the nano-light-mixer (NLM) array addressing this hurdle. Silicon surface nanopillar (NP) arrays have been demonstrated for efficient absorption of solar power. In this work, a NP is deformed into an NLM, and a NLM array is formed. The deformation entails the narrowing of the NP bottom diameter, and the introduction of sidewall surface decorations. A numerical investigation demonstrates an enhancement of ~25% in broadband absorption under normal illumination compared with an optimized NP array. A superior omnidirectional absorption is shown. The NLM array broadband absorption is driven by transmission suppression, higher photon penetration depths, and the generation of greater light intensity distributions in the vertical and horizontal directions. Next, NLM and NP arrays are fabricated, and their light trapping properties are examined with a near-field scanning optical microscopy (NSOM). The NSOM is employed to examine the period-dependency of the far-field and near-field responses for a 532 nm excitation (solar spectrum maximum). The NLM array is a promising approach to support optical absorption and light trapping for thin-film technologies.