Indium-tin-oxide free transparent electrodes using a plasmon frequency conversion layer

Abstract

Transparent electrodes to enhance external quantum efficiency (EQE) in optoelectronic devices are proposed based on the suppression of surface plasmons (SPs) at the metal–dielectric (or metal–organic) interface using a frequency conversion layer. Plasmonic absorption at metal-based electrodes causes severe optical losses in the planar stacks of optoelectronic devices. Even though Ag is suitable for transparent electrodes owing to its lowest absorption coefficient compared to other metals, the surface plasmon resonant frequency (SPRF) of Ag is located in the visible region (i.e., ω_SP ∼ 3.9 eV, λ_SP = 500–550 nm). Thus, incident light is absorbed by surface plasmon resonance (SPR) at the interface between Ag and dielectric materials. These plasmonic resonances could be dramatically suppressed by adding a 2 nm-thick Al interlayer with resonance frequency out of the visible region (i.e., ω_SP ∼ 15 eV, λ_SP = 250–300 nm), which results in an extreme enhancement of the optical transmittance of Ag-based electrodes from 68% to 91% at 470 nm. These approaches for highly transparent and conductive multilayer stacks are applicable to universal optoelectronics because they are straightforward, cost-effective and reliable even in large area fabrication.