A study on green organic light-emitting diodes with high electron mobility in hole block and electron transport layers.

The electron mobility and hole blocking ability of BPhen, BCP, and ET137 were investigated by fabricating an electron only device and hole only device, respectively. Although it was observed that ET137 has the highest electron mobility, the device with ET137 as electron transporting layer was unable to obtain high efficiency alone and it was necessary to use a hole blocking layer because of the poor hole blocking ability due to the high-lying HOMO energy level. We fabricated green-emitting phosphorescent devices with various hole blocking layers and electron transporting layers. It was demonstrated that the high electron mobility of the electron transporting layer and hole blocking layer leads to high efficiency in organic light-emitting diodes. The device with BPhen and ET137 as hole blocking layer and electron transporting layer, respectively, showed the best efficiency properties. The maximum values of luminous efficiency, power efficiency, and quantum efficiency were 41.1 cd/A, 26.9 Im/W and 12.4%, respectively.