Abstract
Electroluminescent efficiency of organic light-emitting diodes with Ir-based emitter depends strongly on the nature of the hole transport layer used. The efficiency is not correlated with the oxidation potential of the hole transport material. Instead, we found that many of the hole transport materials used can quench the photoluminescence intensity of the Ir green emitter and the photoluminescent quenching efficiency correlates well with the device efficiency. Based on the pulse radiolysis energy transfer experiments, we established the origin of the photoluminescent quenching as due to energy transfer from the excited state of Ir green emitter to the triplet state of the hole transport material.