White light emission from exciplex in a bilayer device with two blue light-emitting polymers

Abstract
Bilayer polymer light-emitting diodes with two blue light-emitting materials, poly(N-vinylcarbazole) (PVK) and poly(2-dodecyl-p-phenylene) (C12O-PPP), can emit blue or white light, depending on the solvent used in the fabrication of the second layer, C12O-PPP. If hexane (the nonsolvent for PVK) is used, the device emits blue light as a single layer device with C12O-PPP. However, if toluene (the cosolvent for the two polymers) is used, the device emits white light originating from an exciplex emission at the bilayer interface in addition to the exciton emission from C12O-PPP. At low temperatures, the intensity of the exciplex emission drops and that of the exciton emission becomes dominant.