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

• Moth-eye patterned NOA63 films are fabricated on coverglasses by a soft lithography.
• NOA63 nanogratings (NGs) suppress the surface reflection of coverglasses.
• NOA63 NGs/coverglass effectively enhances the efficiency of III–V photovoltaic modules.
• NOA63 NGs/film is very promising for high-performance photovoltaic systems.

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 (TSW) of ~93.2% at an incident angle (θi) of 0° and the larger average TSW value of ~83.6% at θi=10–70° than those (i.e., TSW~90.1% at θi=0° and average TSW value of ~81.5% at θi=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 (JSC) of 14.68 mA/cm2 compared to reference PV modules with the bare coverglass (i.e., PCE=30.12% and JSC=14.07 mA/cm2) at θi=0°. For incident angle-dependent PV module characteristics, it also has more outstanding solar energy conversion properties in a wide θi range of 10–70°.