Influence of thickness of electron transport layer and block layer on the properties of quantum dot light emitting diodes

In view of carrier injection unbalance problem of the quantum dot light emitting diode (QLED), the injection rate of holes and electrons in the quantum dots (QDs) layer was studied. QLED with structure of ITO/PEDOT:PSS/Poly-TPD/QDs/Alq3 was fabricated. The experiment results show that all the devices exhibit red light and the turn-on voltage rises as the Alq3 thickness increases from 25 nm to 45 nm. When the Alq3 thickness is 30 nm, the current efficiency of the device is high and the injection rate of holes and electrons in the QDs layer reaches a relative balance. Then, the luminescence properties of the devices were further studied through imbedding an electron blocking layer TPD into the QDs/Alq3 interface. When the TPD thickness is 1 nm, the device still exhibits red light, and green light begins to appear when the TPD thickness is 3 nm and 5 nm. The experiment results show that a thinner thickness and lower LUMO should be chosen for the electron blocking layer.