Optical performance improvement of semi-transparent metal film electrodes with biomimetic subwavelength gratings for high-performance optoelectronic device applications

Abstract

We fabricated semi-transparent metal electrodes with biomimetic artificial antireflective subwavelength grating (SWG) structures at the surface of an ultraviolet (UV) curable polymer, i.e., Norland Optical Adhesive (NOA) 63, film on polyethylene terephthalate (PET) substrates for semi-transparent optoelectronic applications. The SWG patterns on the NOA63 film/PET were transferred from the silicon master molds with the conical SWG arrays by soft lithography. As a metal electrode, a silver (Ag) layer was deposited on the surface of the NOA63 SWG/PET substrates for different layer thicknesses. Compared with the Ag-coated flat bare PET (i.e., Ag/PET), the Ag/NOA63 SWG/PET showed a superior optical performance over a wide wavelength range of 400–1800 nm. At the Ag layer thickness of 17 nm, the Ag/NOA63 SWG/PET had lower average reflectance (R_avg) and higher average transmittance (T_avg) values of ∼25.1% and ∼33.9% than those (i.e., R_avg ∼ 55.2% and T_avg ∼ 26.4%) of the Ag/PET, respectively, indicating the maximum figure of merit value of 10.23 × 10⁻⁶ ohm⁻¹ (i.e., transmittance of 0.458 at a wavelength of 550 nm and sheet resistance of 39.71 ohm sq.⁻¹). Furthermore, the surface plasmon resonance phenomina (i.e., strong electric and magnetic fields) were observed around the surface of the Ag layer on NOA63 SWGs. Also, it exhibited less angle-dependent optical characteristics at light incident angles of 20–70° under non-polarized light. For optical behaviors, theoretical analyses were also performed by a rigorous coupled-wave analysis method, which gives a similar tendency with the experimentally measured data.