Biomimetic parabola-shaped AZO subwavelength grating structures for efficient antireflection of Si-based solar cells

We report the fabrication and investigation of the parabola-shaped periodic subwavelength grating (SWG) structures on aluminum-doped zinc oxide (AZO) film/Si substrate, which are formed by a novel re-deposition method using the AZO dot arrays as a seed layer, for broadband and omnidirectional antireflection. For fabricated parabola-shaped AZO SWG structures, the antireflection characteristics are investigated, together with theoretical analysis based on a rigorous coupled-wave analysis method. The parabola-shaped AZO SWG structure suppresses significantly Fresnel reflections compared to the AZO film and the AZO dot arrays (or cylindrical AZO SWGs with a hemispherical top) because of its linear gradient-refractive-index change between the AZO and air. For the parabola-shaped AZO SWG/initial AZO film of 600 nm after 45 min re-deposition, it exhibits a low average reflectance of∼5% with a solar weighted reflectance of 5.3% while maintaining a reflectance less than 25.6% over a wide wavelength region of 300–1100 nm up to the incident angle of θ_i=70°. The electrical properties of the fabricated AZO SWG structures are also discussed.