Remarkable improvement in electroluminescence benefited from appropriate electron injection and transporting in ultraviolet organic light-emitting diode

Abstract

Suitable thickness of LiF and 4,7-diphenyl-1, 10-phenanthroline with slightly weakened electron injection and transporting is proposed to match the intractable hole injection capacity in ultraviolet organic light-emitting diode (UV OLED). By using this strategy, the device performance is remarkably improved. With 4,4′-bis(carbazol-9-yl)biphenyl (CBP) and 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ) as emitters, the UV OLED shows maximum radiance of 5.8mW/cm2 and external quantum efficiency of 2.1% with emission peak of ~380nm predominantly from TAZ and noticeable shoulder emission of ~410nm from CBP. The retarded electron injection and transporting contribute to optimizing hole–electron recombination zone and balance within the emitting layers, which accounts for the improved electroluminescent intensity. The detailed mechanism is further clarified with impedance spectroscopy.