Impact of electric fields on the emission from organic light-emitting diodes based on polyvinylcarbazole (PVK)

Influences of electric fields on the emission from organic light-emitting diodes (OLEDs) based on 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and polyvinylcarbazole (PVK) are studied. Electroluminescence (EL) spectra are very different from its photoluminescence (PL) for blend of PVK and BCP in the weight ratio M_PVK:M_BCP=1:3. EL spectrum of device ITO/Blend/BCP(20 nm)/Alq₃(12 nm)/Al maximizes at 500 nm. For trilayer device ITO/PVK/BCP(10 nm)/Alq₃(10 nm)/Al, the relative emission intensity of PVK to BCP, initially increases and then decreases with increasing electric field. Under high electric fields, holes can transport through thinner BCP layer and recombine with electrons in Alq₃ layer.