Hole-transport-layer-free CdSe/ZnS core/shell red quantum-dot light-emitting diodes sensitized by TADF polymers

Abstract

Due to high photoluminescence quantum yields, narrow bandwidths and tunable colors, quantum dot light emitting diodes (QLEDs) have become one of the most promising display technologies. To simplify the device structure and improve the charge transport, a thermally activated delayed fluorescence (TADF) polymer was introduced into the emitting layer as an assistant host in this work. The TADF polymer facilitates the efficient utilization of triplet excitons through reverse intersystem crossing, promoting Förster energy transfer to QDs. By optimizing the host selection, the emission from the TADF polymer itself could be suppressed, which significantly improved the color purity of QLEDs. Without using any hole transport layer, the fabricated CdZnS/ZnS core/shell red QLEDs showed a maximum external quantum efficiency of 18.1%. The cascaded energy transfer in the ternary emitting layer provides a promising strategy to construct highly efficient and simplified QLEDs.