High efficiency and low roll-off white phosphorescent organic light-emitting diodes by employing various acceptor ratio in exciplex-forming co-host

The exciplex-forming co-host system has demonstrated significant potential in the development of high-efficiency white organic light-emitting diodes (WOLEDs). However, there have been limited investigations into the electroluminescence (EL) performance of WOLEDs utilizing exciplex-forming co-hosts with varying electron donor/electron acceptor mixing ratios. In this work, we fabricated two complementary-color WOLEDs by employing PO-01-TB doped in the mCP:PO-T2T exciplexforming co-host and FIrpic doped mCP host as the orange and the blue emission layers, respectively. The effects of various mixing ratios of mCP:PO-T2T on device performance were explored. It was observed that decreasing the PO-T2T content resulted in a blue shift in the emission peak, indicating an increase in the energy of the mCP:PO-T2T exciplex. The enhancement facilitates the energy transfer to the blue phosphor FIrpic, thereby improving the exciton utilization and reducing efficiency roll-off at high luminance. By optimizing the device structure, the all-phosphorescent warm WOLED using mCP:PO-T2T (2:1) exciplex host was achieved with a maximum EQE of 21.1 %, which remained 20.6 % at 100 cd/m2 and 18.4 % at 1000 cd/m2, demonstrating high EQE and low efficiency roll-off.