Improved Efficiencies in Organic Light Emitting Diodes Made with CdSe/ZnS Quantum Dots and a Semiconducting Polymer

In this study, we report the fabrication and characterization of organic/inorganic hybrid polymer light emitting diodes (PLEDs) made with ZnS-capped CdSe core/shell type nanocrystals and a light-emitting polymer poly[2-phenyl-3-(9,9-dihexylfluoren-2-yl)-1,4-phenylene vinylene]-co-[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene]. The device using pristine polymer as active layer emitted yellow light with a maximum brightness of 3949 cd/m(2) and maximum external quantum efficiency of 0.27 cd/A at 10 V. After blending with the CdSe/ZnS quantum dots (QDs), the device showed a much higher brightness of 8192 cd/m(2) and external quantum efficiency of 1.27 cd/A at 7 V, while the driving voltage was lowered. The experimental results revealed that CdSe/ZnS QDs act as a hole-blocker in the devices. More efficient electron-hole recombination process inside polymer layer results in large improvement in luminescence and efficiency.