Poly[2-(N-carbazolyl)-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]/tris (8-hydroxyquinoline) aluminum heterojunction electroluminescent devices produced by cluster beam deposition methods

We have fabricated and characterized double-layer-type electroluminescent devices with the structure of indium-tin-oxide-coated glass/poly[2-(N-carbazolyl)-5-(2-ethylhexyloxy)-1, 4-phenylenevinylene] (CzEH-PPV)/tris(8-hydroxyquinoline) aluminum (Alq₃)/Li:Al, in which CzEH-PPV was used as a hole transport medium, and neutral and ionized cluster beam deposition (NCBD and ICBD) methods were applied to deposit Alq₃. The surface morphology observed by atomic force microscopy shows that NCBD and especially ICBD methods are more efficient in producing flat and smooth thin film surfaces in comparison to the conventional physical vapor deposition method. Studies of photoluminescence, electroluminescence (EL), and device characteristics demonstrate that the polymeric thin film is susceptible to ion radiation damage and the NCBD-based devices show better device performance, including lower threshold and turn-on voltages, improved EL intensity-voltage, current density-voltage, and external quantum efficiency (EQE)-current characteristics. In addition, the doping effect of the highly fluorescent dye molecule 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran into the Alq₃ layer reveals a complete energy transfer, color-tuning capability and enhanced EQEs.