Performance improvement of polymer light-emitting diodes based on fluorene copolymer with cesium fluoride/aluminum cathode

Polymer light-emitting diodes with saturated red emission were fabricated using the copolymer, poly [2, 749, 9-dioctyl) fluorene-co-5, 5'-(4, 7-diselenophenyl) -2,2'-yl-2, 1, 3-benzothiadiazole] (PFO-SeBT). Special attention was paid to polymer/electrode interface modification. The highest eleetroluminescence external quantum efficiency of 1.79%, which was more than twice that of devices with low work function metal cathode Ba/Al, was achieved by incorporation of CsF/Al cathode with carefully optimized thickness of CsF, and insertion of PVK layer in the PFO-SeBTI/anode interface. Efficient improvement of electron injection of CsF/Al cathode and blocking effect of PVK to electrons were proposed to be responsible for the improved performances of the device.