Improved film morphology and reduced defects in solution-processed red phosphorescent emission layer of the organic light-emitting diodes

Abstract The fabrication of highly efficient organic light-emitting diodes (OLEDs) by solution processes has become a hot research point due to the low production cost, high material utilization ratio and simple fabrication process. Herein, highly efficient, solution-processed red phosphorescent organic light-emitting diodes (PhOLEDs) using chlorobenzene (CB) and isopropanol (IPA) as mixed solvents are proposed. It is found that both the roughness and the defect states of emission layer (EML) prepared with mixed solvents are reduced. Thereby, the electroluminescence performance of PhOLEDs are enhanced compared with that of the ones with pure CB as the solvent. With CB:IPA ratio of 5:1, the current efficiency and the external quantum efficiency of device reach 27.1 cd/A and 17.2 %, respectively. These results prove that the use of IPA can improve the device performance even if it is not able to dissolve the organic materials, which breaks the limitation of the use of alcohol solvent in solution-processed OLEDs.