Highly efficient and eco-friendly InP-based quantum dot light-emitting diodes with a synergetic combination of a liquid metal cathode and size-controlled ZnO nanoparticles

Abstract

Colloidal quantum dot light-emitting diodes (QLEDs) are the most promising candidates for next-generation displays due to wide color gamut, high contrast ratio, and narrow bandwidth emission. However, high efficiency QLEDs based on toxic cadmium-based quantum dots (QDs) are strictly regulated by environmental law, and therefore environmentally friendly fabrication methods using non-cadmium-based QDs are indispensable for industrial applications. In this study, an eco-friendly and scalable fabrication strategy based on a synergetic combination of colloidal InP QDs, a eutectic gallium-indium liquid metal, and size-controlled ZnO nanoparticles was developed to produce highly efficient, environmentally friendly, solution-processable QLEDs. The cathode electrode of a gallium alloy liquid metal was applied using a simple screen-printing method, and the InP/GaP/ZnS green QDs with an excellent photoluminescence quantum yield of 85% were facilely prepared and incorporated into the device through spin coating process, ensuring that high device efficiency of InP-based QLED was achieved through uniform electroluminescence of active area. In addition, a size-controlled synthetic method for ZnO nanoparticles as the electron transfer layer was developed to improve the quantum efficiency of InP QDs, and consequently the optoelectronic performance of the resulting device was higher than that of conventional device in terms of current density, luminance, and external quantum efficiency.