Flexible Transparent Electrodes Formed from Template-Patterned Thin-Film Silver.

Abstract

Template-patterned, flexible transparent electrodes (TEs) formed from an ultrathin silver film on top of a commercial optical adhesive - Norland Optical Adhesive 63 (NOA63) - are reported. NOA63 is shown to be an effective base-layer for ultrathin silver films that advantageously prevents coalescence of vapor-deposited silver atoms into large, isolated islands (Volmer-Weber growth), and so aids the formation of ultrasmooth continuous films. 12 nm silver films on top of free-standing NOA63 combine high, haze-free visible-light transparency (T ≈ 60% at 550 nm) with low sheet-resistance ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msub><mi>R</mi> <mi>s</mi></msub> <annotation>${\mathcal{R}}_s$</annotation></semantics> </math> ≈ 16 Ω sq^-1), and exhibit excellent resilience to bending, making them attractive candidates for flexible TEs. Etching the NOA63 base-layer with an oxygen plasma before silver deposition causes the silver to laterally segregate into isolated pillars, resulting in a much higher sheet resistance ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msub><mi>R</mi> <mi>s</mi></msub> <annotation>${\mathcal{R}}_{s}$</annotation></semantics> </math>  > 8 × 10⁶ Ω sq^-1) than silver grown on pristine NOA63 . Hence, by selectively etching NOA63 before metal deposition, insulating regions may be defined within an otherwise conducting silver film, resulting in a differentially conductive film that can serve as a patterned TE for flexible devices. Transmittance may be increased (to 79% at 550 nm) by depositing an antireflective layer of Al₂O₃ on the Ag layer at the cost of reduced flexibility.