Pure Mg Cathode for\nHighly Efficient Single-Layer\nOrganic Light-Emitting Diodes

Highly efficient single-layer organic light-emitting\ndiodes (OLEDs)\nare demonstrated by using a pure Mg cathode that is seeded with a\nsmall amount of Ag nucleation sites. Bis(4-phenylthieno[3,2-<i>c</i>]pyridinato-<i>N</i>,C2’)(acetylacetonate)iridium(III)\n(PO-01)-doped devices with three-, two-, and one-region doping configurations\nexhibit maximum external quantum efficiency (EQE) values of 22.8%,\n21.7%, and 11.2%, respectively, which are the highest reported to\ndate for orange single-layer OLEDs. Moreover, the EQE of the one-region\ndevice can be raised to 18.2% when using a codopant to balance electron\nand hole traps. Charge transport characteristics are also investigated\nby single-carrier devices, which reveal that bipolar hosts with well-balanced\nhole and electron transport are not a prerequisite for achieving high-efficiency\nsingle-layer OLEDs; instead, dopants play a crucial role in determining\nthe location of the recombination zone due to the charge trapping\neffect.