Ultrathin Electron Injection Layer on Indium–Tin Oxide Bottom Cathode for Highly Efficient Inverted Organic Light-Emitting Diodes

We have fabricated a highly efficient inverted bottom-emission organic light-emitting diode (IBOLED) based on an indium–tin oxide (ITO) bottom cathode deposited with an ultrathin 1 nm layer of Mg to promote electron injection. The threshold voltage of this IBOLED with a structure of ITO/Mg/Alq 3 /NPB/WO 3 /Al was 4.2 V and an efficiencies of 4.66 cd/A and 1.51 lm/W were achieved at an operational voltage of 8.9 V and a brightness of 940 cd/m 2 . In comparison with an ITO/Alq 3 bottom cathode composition, a reduction in drive voltage from 13.8 to 7.8 V in voltage was obtained at 1 mA/cm 2 . A charge-transfer dipole model is proposed to rationalize the enhanced electron injection.