Efficiency enhancement of organic light-emitting diodes with an oxygen-plasma-treated ITO substrate and an electron-injection layer of alkali-metal carbonates

The efficiency enhancement of organic light-emitting diodes with an oxygen-plasma-treated substrate and an electron-injection layer of alkali-metal carbonates (Li 2 CO 3 and Cs 2 CO 3 ) was studied. The Li 2 CO 3 and the Cs 2 CO 3 carbonates were thermally evaporated to a thickness of 1 nm. For the device with a Li 2 CO 3 layer, the luminance at 9.25 V of the device with the plasma-treated ITO substrate was found to be improved by approximately 10% compared to that of the device with the plasma-untreated ITO substrate, and the maximum luminance driving voltage was lowered by 1.0 V. For the device with a Cs 2 CO 3 layer, the luminance at 11.25 V of the device with the oxygenplasma-treated ITO substrate was found to be improved by approximately 42.3% compared to that of the device with plasma-untreated ITO substrate, and the maximum luminance driving voltage was lowered by 1.25 V. Especially, the luminous efficiencies of the devices with the Li 2 CO 3 and the Cs 2 CO 3 layers were confirmed to have been increased by 50.0% and 78.1%, respectively, when the oxygen-plasma-treated ITO substrate was used.