We report on the attainment of broadband white light emission from a host-guest light-emitting electrochemical cell, comprising a blue-emitting conjugated polymer as the majority host and a red-emitting small-molecule triplet emitter as the minority guest. An analysis of the energy structure reveals that host-to-guest energy transfer can be effectuated by both Förster and Dexter processes, and through a careful optimization of the active material composition partial energy transfer and white emission is accomplished at a low guest concentration of 0.5%. By adding a small amount of a yellow-emitting conjugated polymer to the active material, white light emission with a high color rendering index of 79, and an efficiency of 4.3 cd/A at significant luminance (>200 cd/m(2)), is realized.
Keywords: conjugated polymer; energy transfer; light-emitting electrochemical cell; solid-state lighting; triplet emission; white luminance.