A direct evidence for the energy transfer from phosphorescent molecules to quantum dots in a driving light emitting diode

The energy transfer (ET) processes are considered to enhance the emission in the organic/inorganic quantum dots (QDs) hybrid structures. And efficient QDs based light emitting diodes (QLEDs) have been widely reported by employing this hybrid device design. However, such ET processes have so far been only verified in the photoluminescence regime. Therefore, it is insufficient and unconvincing to elaborate the electroluminescence (EL) mechanism in the devices. Here we for the first time demonstrate the ET process between phosphorescent bis(4,6-difluorophenylpyridinato-N,C2)-picolinatoiridium (FIrpic) and QDs in a QLED under the electrical excitation regime by means of transient EL technology. The prolonged EL decay in the transient EL spectrum confirms that the FIrpic molecules with long exciton lifetime, just like an exciton reservoir, can harvest both the leaked electrons from the QDs and holes injected from hole transport layer, which then form excitons and transfer their energy to the QDs.