Vacuum-Deposited versus Spin-Coated Emissive Layers for Fabricating High-Performance Blue-Green-Emitting Diodes

The electroluminescent characteristics of two sublimable cationic iridium(III) complexes that bear the same coordinated iridium(III) cation but different tetraphenylborate-type negative counterions have been investigated. Blue-green-emitting devices were successfully fabricated from these complexes using various preparation processes, namely, spin-coating and vacuum evaporation deposition. Experiments indicated that devices with vacuum-deposited emissive layers showed superior photoelectric properties relative to devices with spin-coated emissive layers, including a maximum current efficiency of 27.91 cd A^-1 , an external quantum efficiency of 10.48 %, a power efficiency of 27.73 lm W^-1 and the highest luminance of up to 25.34×10³  cd m^-2 , whereas the turn-on voltages were quite low. The overall device performance surely ranks among the best of phosphorescent organic light-emitting diodes based on ionic transition-metal complexes.