Solution-processible N-P=O resonance-host molecules are applied successfully in spin-coated phosphorescent light-emitting diodes (PHOLEDs) to selectively and self-adaptively tune the electrical properties for balanced charge transportation. The resonance-molecule-hosted PHOLEDs exhibit a high maximum quantum efficiency of 16.5% and a low efficiency roll-off down to 0.7%, highlighting the significant progress of these solution-processed PHOLEDs with high efficiency and flat efficiency roll-off achieved simultaneously.