Ultrathin electron injection layer on indium-tin oxide bottom cathode for highly efficient inverted organic. light-emitting diodes

Abstract

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/WO3/Al was 4.2V and an efficiencies of 4.66cd/A and 1.51 1m/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.