Integrated three-dimensional photonic nanostructures for achieving near-unity solar absorption and superhydrophobicity

In this paper, we proposed and realized 3D photonic nanostructures consisting of ultra-thin graded index antireflective coatings (ARCs) and woodpile photonic crystals. The use of the integrated ARC and photonic crystal structure can achieve broadband, broad-angle near unity solar absorption. The amorphous silicon based photonic nanostructure experimentally shows an average absorption of & SIM;95% for lambda = 400-620 nm over a wide angular acceptance of theta = 0 & DEG;-60 & DEG;. Theoretical studies show that a Gallium Arsenide (GaAs) based structure can achieve an average absorption of > 95% for lambda = 400-870 nm. Furthermore, the use of the slanted SiO2 nanorod ARC surface layer by glancing angle deposition exhibits Cassie-Baxter state wetting, and superhydrophobic surface is obtained with highest water contact angle theta(CB) & SIM; 153 & DEG;. These properties are fundamentally important for achieving maximum solar absorption and surface self-cleaning in thin film solar cell applications.