Characteristics of blue organic light emitting diodes with different thick emitting layers

• Driving voltage increases in blue organic light emitting diode (OLED) with increasing the emitting layer (EML) thickness.
• Current efficiency and external quantum efficiency decrease when the EML thickness deviates from 35 nm.
• Luminance of 10,000 cd/m2 is obtained at low voltage of 5.0 V from OLED with EML of 15 nm thickness.

We fabricated blue organic light emitting diodes (called blue OLEDs) with emitting layer (EML) of diphenylanthracene derivative 9,10-di(2-naphthyl)anthracene (ADN) doped with blue-emitting DSA-ph (1-4-di-[4-(N,N-di-phenyl)amino]styryl-benzene) to investigate how the thickness of EML and hole injection layer (HIL) influences the electroluminescence characteristics. The driving voltage was observed to increase with increasing EML thickness from 15 nm to 70 nm. The maximum external quantum efficiency of 6.2% and the maximum current efficiency of 14 cd/A were obtained from the OLED with 35 nm thick EML and 75 nm thick HIL. High luminance of 120,000 cd/m2 was obtained at 7.5 V from OLED with 15 nm thick EML.