Solution-processed small molecule-based blue light-emitting diodes using conjugated polyelectrolytes as electron injection layers

摘要

Organic blue light-emitting diodes were studied using the solution processable small molecule 2,7-dipyrenyl-9,9'-dioctyl-fluorene (DPF) as the light-emitting material. The devices were fabricated in two simple structures: indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/DPF/LiF/Al and ITO/PEDOT: PSS/DPF/PFN-BIm_4/Al, where PFN-BIm_4 is poly[9,9'-bis[6"-(N,N,N-trimethylammonium) hexyl]fluorene-alt-co-phenylene] with tetrakis(imidazolyl)borate counterions. The LiF or PFN-BIm_4 act as electron injection layers. The ITO/PEDOT:PSS/DPF/PFN-BIm_4/Al device, in which all organic layers are cast from solution, has a turn-on voltage of 3.8 V, a luminance of 2000 cd/m~2, and an efficiency of 0.6 cd/A. Using the PFN-BIm_4 layer shows a significant improvement of the device performance when compared to the LiF layer.