Spirobifluorene modified electron transport materials for high efficiency in phosphorescent organic light-emitting diodes

Abstract

Spirobifluorene modified materials, 2,7-bis(4,6-diphenyl-1,3,5-triazin-2-yl)-9,9′-spirobi[fluorene] (SBFTrz), 2,7-bis(4-phenylbenzo[4,5]thieno[3,2-d]pyrimidin-2-yl)-9,9′-spirobi[fluorene] (SBFBTP) and 2,7-bis(4-phenylbenzofuro[3,2-d]pyrimidin-2-yl)-9,9′-spirobi[fluorene] (SBFBFP), which have good electron transport and thermal properties were developed as electron transport layers (ETLs). The common core, spirobifluorene, is good for transporting carriers due to two fluorene units perpendicular to each other and has a high triplet energy due to disconnection of conjugation through the sp³ carbon. Additionally, the electron transport moieties of diphenyltriazine, benzothienopyrimidine, and benzofuropyrimidine can provide good electron transport properties and high triplet energy. Therefore, the combination of the spirobifluorene core with the electron transport units offered ETLs overperforming a conventional ETL. The new ETL materials lowered device driving voltage, enhanced quantum efficiency, and more than doubled the lifetime of green phosphorescent organic light-emitting diodes.