Broadband and omnidirectional highly-transparent coverglasses coated with biomimetic moth-eye nanopatterned polymer films for solar photovoltaic system applications

Highly-transparent coverglasses coated with broadband and omnidirectional antireflective (AR) moth-eye nanopatterned ultra-violet (UV) curable polymer, i.e., Norland Optical Adhesive (NOA) 63, films are reported. The moth-eye nanopatterns on the NOA63 polymer films/glasses are transferred from the silicon molds with conical nanogratings (NGs) using poly-dimethylsiloxane stamps by a soft imprint lithography technique. For the NOA63 NGs/glasses, surface wetting behaviors, UV radiation/thermal effects, and optical properties, together with theoretical analyses using rigorous coupled-wave analysis calculations, are investigated. For a period of 380 nm, the NOA63 NGs/glass exhibits a hydrophobic surface with a water contact angle of ∼112°. Furthermore, it increases the transmittance of the bare glass over a wide range of wavelengths and incident light angles, showing the higher solar weighted transmittance (T_SW) of ∼93.2% at an incident angle (θ_i) of 0° and the larger average T_SW value of ∼83.6% at θ_i=10-70° than those (i.e., T_SW∼90.1% at θ_i=0° and average T_SW value of ∼81.5% at θ_i=10-70°) of the bare glass in the wavelength range of 350-1800 nm. In addition, it shows a relatively good stability under intense UV radiation and high temperature. By employing the 380 nm-period NG patterned NOA63 films into an AR coating of coverglasses in encapsulated III-V GaInP/GaInAs/Ge triple-junction solar photovoltaic (PV) sub-receiver modules, an enhanced power conversion efficiency (PCE) of 31.33% is obtained mainly due to an increased short-circuit current density (J_SC) of 14.68 mA/cm² compared to reference PV modules with the bare coverglass (i.e., PCE=30.12% and J_SC=14.07 mA/cm²) at θ_i=0°. For incident angle-dependent PV module characteristics, it also has more outstanding solar energy conversion properties in a wide θ_i range of 10-70°.