Highly efficient hybrid light-emitting device using complex of CdSe/ZnS quantum dots embedded in co-polymer as an active layer

We propose a highly efficient hybrid light-emitting device (LED) with a single active layer where CdSe/ZnS quantum dots (QDs) are dispersed as a guest material in a conjugated polymer (co-polymer) matrix used for a host material. In our structure, the QDs act on light-emitting chromophores by trapping the migrating excitons in the co-polymer matrix via Förster energy transfer, and improve the charge balance within the copolymer by trapping the injected electron carriers. Experimental results show that the electroluminescent properties highly depend on the doping density of the QDs within the co-polymer matrix, where the luminance as well as the external current efficiency are initially enhanced with increasing the concentration of the dispersed QDs in the co-polymer solution, and then such properties are degraded due to aggregation of the QDs. We can get the maximum brightness of 9,088 cd/m² and the maximum external current efficiency of 7.5 cd/A in mixing ratio of the QDs by 1.0 wt%. The external current efficiency is enhanced by over 15 times and the turn-on voltage is reduced in comparison with the corresponding values for a reference device that uses only a co-polymer as an active layer.