Quantum-dot light-emitting diode with ultrathin Au electrode embedded in solution-processed phosphomolybdic acid

Abstract

We proposed to exploit phosphomolybdic acid (PMA) as a cost-efficient MoO_x source for combined spin-coating/sputtering/spin-coating deposition of a MoO_x/Au/MoO_x (MAM) composite electrode. The bottom PMA layer provides perfect wetting conditions for ultrathin Au film sputtering and prevents the formation of gold islands on the glass surface, while the top PMA layer helps to reduce light reflection. By optimizing the thickness of ultrathin Au films and PMA layers, we achieved maximum transmittance of 79% at 550 nm and a sheet resistance of only 22 Ω sq⁻¹ which is comparable to the resistance of ITO substrates (20 Ω sq⁻¹). MAM multilayer was explored both as a transparent electrode and as a hole injection layer (HIL) to eliminate ITO and PEDOT:PSS from solution-processed quantum-dot light-emitting diodes (QLEDs). The fabricated MAM-based QLED shows a peak external quantum efficiency (EQE) of 2.7% and maximum brightness of 12 000 cd m⁻² at 7 V. By performing bending tests of the polyethylene (PET) substrate coated with MAM electrode, we demonstrate that it is also a promising candidate for flexible transparent optoelectronics.