Highly efficient and emitter concentration insensitive phosphorescent electroluminescent devices based on a novel rhenium(I) [Re(I)] complex, i.e., (4,5-diaza-9,9′-spirobifluorene)R (CO)₃Br (Re-DSBF), were established. Non-doped device based on Re-DSBF as emitter exhibited outstanding performances with the peak luminance of 8531 cd m⁻² and maximum current efficiency of 16.8 cd A⁻¹, which were the highest reported to date for non doped phosphorescent electroluminescent devices based on Re(I) emitters. Such excellent performances are closely related to the steric hindrance, large Stokes shift, and short luminescent lifetime of Re-DSBF complex. The luminescent mechanisms of those devices were also investigated.