Organic light-emitting diodes with improved hole-electron balance by using molecular layers of phthalocyanine to modify the anode surface

By using the Langmuir-Blodgett (LB) technique, well-defined molecular layers of 2,9,16-tri(tert-butyl)-23-(10-hydroxydecyloxy)phthalocyanine were fabricated. These LB films have been employed to modify an anode surface of organic light-emitting devices. The insertion of LB films between an indium tin oxide (ITO) and hole-transport layers leads to an increase in device efficiency as a result of an improvement of the balanced carrier injection. An external quantum efficiency of 0.88% and a brightness of 10840 cd/m² for a device with a structure of ITO/two LB layers/N, N′-diphenyl-N, N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD)/tris(8-hydroquinolinato)aluminium (Alq₃)/Al were obtained, while the external quantum efficiency and brightness for the device without LB layers of ITO/TPD/Alq₃/Al were 0.51% and 5744 cd/m², respectively.