Antireflection Mechanism and Reflectance Optimization Modeling of Three‐Level Hierarchical Micro‐Nano Structures

Although laser‑processed hierarchical micro‑nano structures hold great potential for silicon antireflection, it remains difficult to quantitatively correlate complex multi‑scale morphological features with optical response. This work addresses this bottleneck by developing a multi‐scale semi‐analytical reflectance model. Utilizing three‐level micro‐nano structures reported in our prior study, which were fabricated by our two‐step nanosecond laser‐assisted waterjet and femtosecond laser processing, we reveal the respective antireflection mechanisms of each structural level. The microscale V‐grooves provide a light‐trapping effect; laser‐induced periodic surface structures (LIPSS) promote light absorption via multi‐order grating diffraction inside the silicon substrate while resulting in negligible non‐zero‐order reflection toward air; and random nanoparticles mitigate the abrupt change in interfacial refractive index via the effective medium effect. Integrating ray tracing, grating diffraction, effective medium layer thin‐film interference and nanoparticle scattering, the proposed model predicts that structure reflectance drops with rising V‐groove aspect ratio while being nearly insensitive to groove width. The model establishes a quantitative relationship between hierarchical structural parameters and reflectance, enabling parameter‐guided design of laser‐textured silicon antireflection surfaces. Experimental validation confirms the predictive capability of the model, with the optimized structure achieving a minimum reflectance of 4.5% within 300–1000 nm.