Comparative studies on EL performances of the OLEDs prepared by PVD, NCBD and ICBD methods

Organic light emitting diodes (OLEDs) with the structure of indium-tin-oxide glass/spin-coated poly[2-(N-carbazolyl)-5-(2-ethyl-hexyloxy)-1,4-phenylenevinylene]/8-hydroquinoline aluminum/Li:Al [ITO-glass/CzEH-PPV/Alq(3)/Li:Al] have been fabricated by applying three deposition methods: physical vapor deposition (PVD), neutral and ionized cluster beam depositions (NCBD and ICED). Atomic force microscopy (AFM) measurements show that the weakly bound and highly directional cluster beam is effective in producing uniform flat film surfaces. Photo- and electro-luminescence (PL, EL) spectra demonstrate that the NCBD and PVD methods produce more efficient EL devices and the introduction of neutral buffer layer to the ICED devices enhances the performances. DCM-doped devices show color-tuning capability and higher external quantum efficiency (EQE) compared to undoped devices.