Abstract
The low efficiency and fast degradation of devices from ink-jet printing process hinders the application of quantum dot light emitting diodes on next generation displays. Passivating the trap states caused by both anion and cation under-coordinated sites on the quantum dot surface with proper ligands for ink-jet printing processing reminds a problem. Here we show, by adapting the idea of dual ionic passivation of quantum dots, ink-jet printed quantum dot light emitting diodes with an external quantum efficiency over 16% and half lifetime of more than 1,721,000 hours were reported for the first time. The liquid phase exchange of ligands fulfills the requirements of ink-jet printing processing for possible mass production. And the performance from ink-jet printed quantum dot light emitting diodes truly opens the gate of quantum dot light emitting diode application for industry.
Highlights
The low efficiency and fast degradation of devices from ink-jet printing process hinders the application of quantum dot light emitting diodes on generation displays
Together with the benefits from the efficient trap states passivation and stronger binding, we demonstrated that inkjet printing (IJP) processed quantum dot light emitting diodes (QLEDs) could achieve external quantum efficiency (EQE) of 16.6% and operation lifetime (LT95@1000nits) of 1833 h
X-ray diffraction (XRD) confirmed that the crystal structure of our QDs is wurtzite (Supplementary Fig. 1), the (100) wurtzite zinc selenide (ZnSe) surface model is chosen to study the trap states induced by under-coordinated anion and cation sties on the surface
Summary
The low efficiency and fast degradation of devices from ink-jet printing process hinders the application of quantum dot light emitting diodes on generation displays. Extensive engineering of core/shell structures has been carried out in previous reports including gradient intermedium shell and smaller energy gap shell martials With these methods, the external quantum efficiency (EQE) over 20% has been achieved and half lifetime of QLED device has reached over 2,000,000 h1–3,19. Several studies tried different types of ligands to eliminate trap states for better device efficiency[19,24,25], there is no effort to passivate both ionic traps in QLEDs. On the other hand, ligands play important roles in the compatibility of the inkjet printing solution process. Mixed passivation by two ligands was proposed[11,12], due to the relatively low ligand exchange coverage and the negative influence on optoelectrical property, it is challenging to obtain both sufficient passivation for dual traps and good emitting property of CQDs
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