Triplet exciton confinement in phosphorescent polymer light-emitting diodes

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Abstract
A series of iridium complexes, with triplet energy levels above or below the triplet level of host polymer, were used to study the flow of excitons between the host and the dopants. The performance of phosphorescent polymer light-emitting diodes has been shown to be sensitive to the triplet energy of the dopant. When the dopant exciton level was higher than that of the host polymer, a “backward excitation energy transfer” occurred; hence, the photoluminescence is quenched and the device performance is poor. When the triplet energy level of the dopant was lower than that of the host polymer, the exciton is confined to the dopant site, and the device shows better performance due to this confinement.