Novel hole blocking material for organic light-emitting devices

Abstract

Two novel boron complexes, i.e, bis (dimesitylboron) stilbene (DMBSB) and bis (dimesitylboronphenyl) acetylene (DMBPA) with the lowest unoccupied molecular orbital (LUMO) of 3.0 eV and the highest occupied molecular orbital (HOMO) of about 6.3 eV.are reported in the paper. Compared to bathocuproine (BCP), the characteristics of two novel materials as hole blocking layer (HBL) were studied in triple layer organic light-emitting devices (OLEDs). The OLEDs were fabricated by conventional thermal vacuum deposition using N, N'-biphenyl-N, N'-bis-(1-naphenyl)-1, 1'-biphenyl -4, 4'-diamine (NPB) as a hole transporting layer (HTL), and tris (8-hydroxyquinolinato) aluminum (Alq) as an electron transport layer (ETL). The results showed that DMBSB efficiently confines the exciton recombination zone into the HTL (NPB layer), and the devices have a current density of 600 mA/cm² at 19.5 V with a luminance of 504 cd/m², and a turn-on voltage of 7.7 V. The device of DMBPA material as the HBL has green light emission even with current density of 532 mA/cm² and a maximum luminance of 1000 cd/m² at 20 V, and a turn-on voltage of 7.9 V. The electroluminescent (EL) spectrum showed an emission peak at 516 nm with a shoulder at 429 nm, corresponding to CIE coordinates of (0.28, 0.40), which indicates that light emission from Alq layer and NPB layer occurres simultaneously.