The relationship between the substitution position of the diphenylphosphine oxide on the spirobifluorene and device performances of blue phosphorescent organic light-emitting diodes

A high triplet energy host (SPPO11) with a diphenylphosphine oxide group attached to the 4 position of the spirobifluorene was synthesized and its device performances were compared with those of the triplet host with the diphenylphosphine oxide at the 2 position of the spirobifluorene (SPPO1). The thermal stability of the SPPO11 was much better than that of the SPPO1 and the efficiency of the blue PHOLED with the SPPO11 host was higher than that of the blue PHOLED with the SPPO1 host. The SPPO11 could be effectively used as the high triplet energy host in the blue PHOLED and a high quantum efficiency of 17.2% and a current efficiency of 35.3 cd/A were obtained in the blue PHOLED with the SPPO11 host.