Recently, Professor Du Zuliang reported that the use ofQDs@PFN as a light-emittinglayer, which solved the problem of large hole injection barrier at the hole transport layer/light-emitting layer interface in the quantum dot light emitting diodes (QLEDs). The research work is published inOrganic Electronics, 2019, 66, 110–115. (SCI, IF=3.68)

https://doi.org/10.1016/j.orgel.2018.11.045

For solution-processed quantum dot light-emitting diodes (QLEDs), improving hole injection efficiency to balance carriers in the emitter is a priority for achieving high device performance. Aiming at this, we introduce a new strategy by utilizing advantage of special properties of poly [(9,9-bis(3’-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-ioctyl-fluorene)(PFN), in which a small amount of PFN is simply mixed with CdSe/CdS/ZnS QDs (QDs@PFN) as emitting layer (EML). For QDs@PFN EML, the PFN additive not only can appreciably upshift the valence band maximum (VBM) of the QDs layer by 0.41 eV through interaction between its lone-pair electrons of the nitrogen atom and the QDs surface, but also maintains efficient electron injection/transport of QDs due to n-type semiconductor property. As a consequence, the hole injection efficiency has been remarkably improved in QDs@PFN EML-based device and then the optimized QLED has been successfully realized with a maximum current efficiency of 16.21 cd A⁻¹and corresponding to the EQE of 14.77%, meaning a 1.8-fold improvement. The results demonstrated that adding a small amount of polymer materials containing aliphatic amine groups into QDs EML could be a simple and effective way to improve hole injection while maintaining effective electron injection/transport in high-performance all-solution-processed QLEDs.