White light emission from a polymer-macromolecule blend system due to energy and charge transfer

The emission color of organic-light-emitting diodes (OLEDs) can be tuned by doping the active layer with fluorescent polymers, dyes or macromolecules. We built white light emitting OLEDs with an external electroluminescence ( EL) quantum efficiency of up to 1.8% by doping a blue-light-emitting ladder type poly(paraphenylene) with an orange emitting fully pi-conjugated macro- molecule. For the EL spectra we found a much stronger contribution from the guest emission than in photoluminescence, which is attributed to charge ca rrier trapping at the guest and subsequent EL in addition to excitation ene rgy migration of singlet excitons from the host to the guest.