Nondoped blue fluorescent organic light-emitting diodes based on benzonitrile-anthracene derivative with 10.06% external quantum efficiency and low efficiency roll-off

摘要

In this manuscript, by utilizing limited conjugation of carbazole and easily realizing triplet-triplet annihilation properties of 4-(anthracen-9-yl)benzonitrile, two new blue materials 4-(10-(9-phenyl-9H-carbazol-3-yl)anthracen-9-yl)benzonitrile (3CzAnBzt) and 4-(10-(4-(9H-carbazol-9-yl)phenyl)anthracen-9-yl)benzonitrile (pCzAnBzt) were designed and synthesized. In both cases, these compounds exhibited small energy gap and orbit overlapped between excited state of T-m and S-n, which would accelerate the triplet-triplet annihilation process. Additionally, when these two compounds were used as emitters in nondoped devices, the triplet energy was utilized efficiently through triplet-triplet annihilation, excellent blue electroluminescence performances were achieved. The maximum external quantum efficiency values were 10.06% and 9.23% for 3CzAnBzt and pCzAnBzt, respectively. The efficiency roll-off for 3CzAnBzt and pCzAnBzt were very low, the EQEs still remained 8.97% and 7.10% at the luminescence of 1000 cd m(-2). (0.14, 0.14) and (0.14, 0.10) are the Commission International de L'Eclairage coordinates for 3CzAnBzt and pCzAnBzt, respectively, at the voltage of 6 V. Up to now, the outstanding EL performances were the state-of-the-art compared to previously reported nondoped blue EL devices.