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

Abstract

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.