We investigated efficient blue organic light emitting diodes (OLEDs) containing fluorescent and phosphorescent emitters in the emitting layer (EML). We fabricated several hybrid blue OLEDs with different thicknesses or switching positions for the fluorescent and the phosphorescent EMLs using the fluorescent deep blue emitter 1,6-Bis(N-phenyl-p-CN-phenylamino)-pyrenes and the phosphorescent blue emitter iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C-2]picolinate. The fabricated device E stacked a 20nm thickness of phosphorescent EML and a 10nm thickness of fluorescent EML. Hybrid blue OLEDs have many advantages in terms of their electrical characteristics, as they have a lower efficiency roll-off than phosphorescent OLEDs and a higher efficiency than fluorescent OLEDs.