Efficient narrowband red electroluminescence from a thermally activated delayed fluorescence polymer and quantum dot hybrid

Abstract

Multiresonant effect is believed to be a promising molecular design rule to solve the bottleneck of wideband electroluminescence (EL) for thermally activated delayed fluorescence (TADF) materials. However, the realization of narrowband red EL still remains a big challenge due to the limited intramolecular charge transfer. Here, a hybrid emitting layer (EML) composed of a TADF polymer and red quantum dots (R-QDs) has been proposed for narrowband EL in red region. Such a hybrid EML can ensure efficient Förster resonance energy transfer and charge trapping to some degree, improve photoluminescent quantum yields, harvest the generated triplet excitons, and favor hole injection/transporting to simply device structure free of hole-transporting layer. As a consequence, the wideband TADF with a full-width at half-maximum (FWHM) of 87 nm is successfully converted to a narrowband red emission with a FWHM of 29 nm. Also, the corresponding device achieves a state-of-art external quantum efficiency as high as 14.9% (16.7 cd A-1, 16.3 lm W-1) together with Commission Internationale de l’Eclairage coordinates of (0.67, 0.32). The results clearly indicate the great potential of the hybrid EML for narrowband red EL.