Efficient light trapping mechanisms in subwavelength surface arrays of light funnel mixers for omnidirectional and broadband absorption of solar energy.

Achieving broadband and omnidirectional solar absorption is critical for advancing high-efficiency photovoltaic technologies. Surface engineering via subwavelength arrays offers a robust pathway for enhanced light trapping. Recently, Light Funnel Mixer (LFM) arrays-comprised of inverted subwavelength cones featuring deep subwavelength sidewall decorations-have demonstrated superior absorption potential. This study investigates the influence of the LFM bottom diameter on light-trapping efficiency using Near-field Scanning Optical Microscopy (NSOM). Two complementary characterization modes are employed: the analysis of far-field distributions under near-field excitation and the mapping of near-field distributions under far-field excitation. The optical response of LFM arrays is benchmarked against standard Light Funnel (LF) and Nanopillar (NP) arrays to isolate the impact of the structural decorations. Our results indicate that, unlike LF structures, LFM arrays exhibit a strong performance dependency on the bottom diameter. Specifically, decreasing the bottom diameter leads to a significant reduction in far-field reflection. Simultaneously, the near-field intensity within the LFM arrays increases as the bottom diameter narrows, indicating enhanced optical excitation and the generation of greater lateral momentum components. These findings directly imply a higher probability of photon absorption in optimized LFM geometries. Experimental observations are corroborated by three-dimensional numerical calculations, providing a comprehensive understanding of the mechanisms governing enhanced light-matter interaction in decorated subwavelength architectures. This work underscores the importance of precise geometric tuning in the design of next-generation solar energy harvesters.