Limits...
The work mechanism and sub-bandgap-voltage electroluminescence in inverted quantum dot light-emitting diodes.

Ji W, Jing P, Zhang L, Li D, Zeng Q, Qu S, Zhao J - Sci Rep (2014)

Bottom Line: Further, the EL from QD-LEDs at sub-bandgap drive voltages is achieved, which is in contrast to the general device in which the turn-on voltage is generally equal to or greater than its bandgap voltage (the bandgap energy divided by the electron charge).The high energy holes induced by Auger-assisted processes can be injected into the QDs at sub-bandgap applied voltages.These results are of important significance to deeply understand the EL mechanism in QD-LEDs and to further improve device performance.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Dongnanhu Road, Changchun 130033, China.

ABSTRACT
Through introducing a probe layer of bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (FIrpic) between QD emission layer and 4, 4-N, N- dicarbazole-biphenyl (CBP) hole transport layer, we successfully demonstrate that the electroluminescence (EL) mechanism of the inverted quantum dot light-emitting diodes (QD-LEDs) with a ZnO nanoparticle electron injection/transport layer should be direct charge-injection from charge transport layers into the QDs. Further, the EL from QD-LEDs at sub-bandgap drive voltages is achieved, which is in contrast to the general device in which the turn-on voltage is generally equal to or greater than its bandgap voltage (the bandgap energy divided by the electron charge). This sub-bandgap EL is attributed to the Auger-assisted energy up-conversion hole-injection process at the QDs/organic interface. The high energy holes induced by Auger-assisted processes can be injected into the QDs at sub-bandgap applied voltages. These results are of important significance to deeply understand the EL mechanism in QD-LEDs and to further improve device performance.

No MeSH data available.


The efficiency versus current density characteristics of the QD-LEDs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4225534&req=5

f7: The efficiency versus current density characteristics of the QD-LEDs.

Mentions: The introduction of FIrpic into the device not only decreases the Vth of the QD-LEDs, but also demonstrates that the concept — inserting a hole block layer to reduce the amount of holes injected into the QDs and consequently improving the charge balance in the QDs — is a good option. As shown in Figure 7, the normalized efficiency is shown as the function of applied current density. The results indicate that the efficiency roll-off of the devices with a FIrpic layer is reduced, which is ascribed to the improved charge balance. The efficiency roll-off of Device F is increased due to the unduly decrease of holes injected into QDs by the thick FIrpic layer, which degenerates the charge balance and efficiency roll-off. Additionally, the peak efficiency of the devices with FIrpic is decreased slightly, which is due to the exciton quenching induced by the accumulated holes at the FIrpic/QDs interface as proposed in our previous report27.


The work mechanism and sub-bandgap-voltage electroluminescence in inverted quantum dot light-emitting diodes.

Ji W, Jing P, Zhang L, Li D, Zeng Q, Qu S, Zhao J - Sci Rep (2014)

The efficiency versus current density characteristics of the QD-LEDs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4225534&req=5

f7: The efficiency versus current density characteristics of the QD-LEDs.
Mentions: The introduction of FIrpic into the device not only decreases the Vth of the QD-LEDs, but also demonstrates that the concept — inserting a hole block layer to reduce the amount of holes injected into the QDs and consequently improving the charge balance in the QDs — is a good option. As shown in Figure 7, the normalized efficiency is shown as the function of applied current density. The results indicate that the efficiency roll-off of the devices with a FIrpic layer is reduced, which is ascribed to the improved charge balance. The efficiency roll-off of Device F is increased due to the unduly decrease of holes injected into QDs by the thick FIrpic layer, which degenerates the charge balance and efficiency roll-off. Additionally, the peak efficiency of the devices with FIrpic is decreased slightly, which is due to the exciton quenching induced by the accumulated holes at the FIrpic/QDs interface as proposed in our previous report27.

Bottom Line: Further, the EL from QD-LEDs at sub-bandgap drive voltages is achieved, which is in contrast to the general device in which the turn-on voltage is generally equal to or greater than its bandgap voltage (the bandgap energy divided by the electron charge).The high energy holes induced by Auger-assisted processes can be injected into the QDs at sub-bandgap applied voltages.These results are of important significance to deeply understand the EL mechanism in QD-LEDs and to further improve device performance.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 3888 Dongnanhu Road, Changchun 130033, China.

ABSTRACT
Through introducing a probe layer of bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (FIrpic) between QD emission layer and 4, 4-N, N- dicarbazole-biphenyl (CBP) hole transport layer, we successfully demonstrate that the electroluminescence (EL) mechanism of the inverted quantum dot light-emitting diodes (QD-LEDs) with a ZnO nanoparticle electron injection/transport layer should be direct charge-injection from charge transport layers into the QDs. Further, the EL from QD-LEDs at sub-bandgap drive voltages is achieved, which is in contrast to the general device in which the turn-on voltage is generally equal to or greater than its bandgap voltage (the bandgap energy divided by the electron charge). This sub-bandgap EL is attributed to the Auger-assisted energy up-conversion hole-injection process at the QDs/organic interface. The high energy holes induced by Auger-assisted processes can be injected into the QDs at sub-bandgap applied voltages. These results are of important significance to deeply understand the EL mechanism in QD-LEDs and to further improve device performance.

No MeSH data available.