Highly efficient blue light-emitting diodes containing spirofluorene derivatives end-capped with triphenylamine/phenylcarbazole

A series of blue fluorescent emitters based on spirofluorene were synthesized via the Horner–Wadsworth–Emmons reaction in moderate yields. Multilayered OLEDs were fabricated with a device structure of ITO/DNTPD (60 nm)/NPB (30 nm)/MADN: Blue dopant materials 1–5 (30 nm)/Alq3 (20 nm)/LiF (1.0 nm)/Al (200 nm). All devices showed efficient blue emission. Among those, device using compound 1 as a dopant material give the best performance with high brightness (2778 cd/m2 at 8.5 V) and high efficiency (4.9 cd/A, 2.3 lm/W, and 4.0% EQE at 20 mA/cm2). The peak wavelength of electroluminescence was 473 nm with CIEx,y coordinates of (0.15, 0.17) at 8.5 V. A deep blue device with CIEx,y coordinates of (0.15, 0.12) at 8.5 V showed a luminous efficiency of 1.8 cd/A and an external quantum efficiency of 1.9% at 20 mA/cm.