High-performance OLEDs based on 4,5-diaza-9,9′-spirobifluorene ligated rhenium(I) complex with enhanced steric hindrance

► A novel synthesized Re(I) complex with large steric hindrance. ► Excellent photophysical properties of the Re(I) complex. ► Superior electron-transporting ability of Re-DSBF. ► Highly efficient and emitter concentration insensitive Re(I)-doped OLEDs. ► Outstanding performances from non-doped device based on Re-DSBF as emitter.