Yellow phosphorescent organic light-emitting device is prepared, and the structure of the device is ITO/HAT-CN/TAPC/TCTA/POAPF…PO-01/Bphen/LiF/Al. The efficiency roll-off of the device fits the triplet-polaron quenching model well. Then, electron-only and hole-only devices are designed. Experimental results show that the holes are majority carriers in light-emitting layer and PO-01 traps holes. The efficiency of the device rolls off drastically due to excitons quenching caused by PO-01 trapping excess holes at high current density. The method of N-doping is used to increase the electron injection, which reduces excess holes in the light-emitting region, improves the carriers balance of the device, and alleviates the excitons quenching caused by excess holes, thereby improving the efficiency roll-off.