Voltage reduction of organic light-emitting device (OLED) with an n-type organic material and a silver cathode

In this paper, a 1.85V reduction in driving voltage of an OLED is presented by using an alkali-metal doped electron transport layer (ETL) and a silver (Ag) cathode. Such an ETL is composed of 2,9-dimethyl-4,7-diphenyl 1,10- phenanthroline (BCP) doped with Cseium (Cs) to increase the conductivity of the organic material and achieve ohmic contact at the ETL/cathode interface regardless the work function of the cathode material. Ag is used to replace the conventional aluminum as the cathode material due to its lower electrical resistivity and optical absorption in visible range. In our devices, the drive voltage was reduced by 1.45V when using MD technique only. When we change the cathode material from Al to Ag, the driving voltage has a further of 0.4V reduction. In those devices, current efficiency is around 3.3 to 4.1 cd/A at 100 mA/cm2.That corresponds to an improvement of 53.36% in power efficiency at 10 mA/cm2.