Spectral studies of thin films based on poly(N-vinylcarzole) and red dopant

Organic light-emitting diodes were fabricated with a structure of indium-tin-oxide (ITO)/poly(N-vinylcarzole)(PVK):4-(dicyanom-ethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)/8-tris-hydroxyquinoline aluminum (Alq3)/lithium fluoride (LiF)/Al. The energy transfer from PVK to Alq3 then to DCJTB and the charge trapping processes were investigated by employing the photoluminescence (PL) and electroluminescence (EL) spectra. With increasing thickness of the Alq3 layer, the PL and EL emission from PVK were decreased gradually, which indicated that the effective energy transfer occurred from PVK to Alq3 and then from Alq3 to DCJTB. At the same time, we found that the exciton recombination zone could be adjusted by controlling the Alq3 layer thickness and the applied voltages. The effects of different DCJTB concentrations on the optical and electrical characteristics of the devices were investigated, and an obvious red-shift was observed with the DCJTB dopant concentrations increasing in the PL and EL spectra.