Improvement of exciton utilization by suppressing exciton leakage for high efficiency blue and white organic light-emitting diodes

The performance of blue organic light-emitting diodes (OLEDs) plays a determinant role in the quality of white OLEDs (WOLEDs). In this paper, we fabricated high efficiency blue OLEDs using a bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato) iridium (FIrpic) doped exciplex composed of 1,3-bis(N-carbazolyl)benzene (mCP) and 4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine (B3PYMPM) as the emitter. In this device, the key to its design was the introduction of a thin DMAC-DPS layer adjacent to the emitter, which not only suppresses the exciton leakage, but also enhances the hole injection. As a result, the turn-on voltage, efficiency and efficiency roll-off of the resulting blue OLEDs were greatly improved. The turn-on voltage was as low as 2.6 V and the maximum external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) reached 23.3%, 46.1 cd A(-1), and 54.9 lm W-1, and remained at 21.9%, 43.2 cd A(-1), and 39.9 lm W-1 at a luminance of 1000 cd m(-2), respectively. Based on the structure of the fabricated blue OLEDs, a warm WOLED with the maximum EQE, CE and PE of 24.7%, 48.2 cd A(-1), and 52.0 lm W-1, and a CRI of over 80 was achieved by further inserting blue, yellow and red phosphorescent materials in the form of ultra-thin layers in a blue emitter.