Efficient, Deep-Blue Organic Electrophosphorescence by Guest Charge Trapping

Recently, efficient blue electrophosphorescence in organic lightemitting devices has been generated by energy transfer from a fluorescent host to a phosphorescent guest molecule. As the energy gap of the guest becomes large, successively larger host energy gaps are required to maintain efficient exothermic energy transfer from host to guest. To alleviate this difficulty, the authors employ host molecules that act as an inert matrix, leaving the guest molecules to both conduct and trap charge, allowing for direct exciton formation on the guest phosphor. This eliminates the need to electrically excite the host, while allowing for efficient carrier collection, exciton formation, and recombination at the guest molecular sites. For efficient emission, however, an exothermic path from host to guest must be maintained to eliminate the transfer of excitons formed on guest molecules back to the lower energy host molecules.