Direct monitoring of recombination zone shift during lifetime measurement of phosphorescent organic light-emitting diodes

Recombination zone of phosphorescent organic light-emitting diodes during lifetime measurement was directly monitored using a red sensing layer inserted at different positions of blue phosphorescent emitting layer. The shift of recombination zone could be identified by the change of red intensity of the red sensing layer because the red intensity reflects the exciton density around the red sensing layer. Gradual shift of the recombination zone from hole transport layer side to electron transport layer side could be directly tracked according to driving time of the device.