Exciplex emission from bilayers of poly(vinyl carbazole) and pyridine based conjugated copolymers

We present photoluminescence and electroluminescence studies of bilayers and blends formed from poly(vinyl carbazole) (PVK) and poly(pyridyl vinylene phenylene vinylene) (PPyVPV) copolymer derivatives. Bilayers of PVK and the PPyVPV copolymers have a photoluminescence emission which cannot be assigned to either the photoluminescence of PVK or the PPyVPV layer. The blends of the two polymers show a similar new photoluminescence emission for a large range of concentrations. Absorption and photoluminescence excitation spectra confirm that the additional feature is an excited state species which results from an exciplex at the polymer/polymer interface. Bilayer light-emitting devices utilizing the PPyVPV copolymers show an electroluminescence spectrum consistent with emission from the exciplex. The efficiency of the bilayer devices as compared to single layer devices increases by over three orders of magnitude due to the exciplex formation and the elimination of exciton formation near the luminescence quenching electrodes.