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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 schematic work mechanism in QD-LEDs, direct charge-injection (left) and energy-transfer (right). charges injection into QDs,  electrons injection into HTL, and  energy transfer from HTL molecules to QDs.
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f1: The schematic work mechanism in QD-LEDs, direct charge-injection (left) and energy-transfer (right). charges injection into QDs, electrons injection into HTL, and energy transfer from HTL molecules to QDs.

Mentions: As is well-known, there are two mechanisms proposed to explain the EL processes in QD-LEDs111213. For the first one, carriers transported through charge-transport layers are directly injected into QDs, where they can form excitons that then can radiatively recombine, as shown in Fig. 1 (left panel). The second one depends on the ability to form excitons on the organic molecules surrounding the QD film that then resonantly transfer the exciton energy to QDs. This work mechanism is schematically shown in Fig. 1 (right panel). Hereafter, we refer to the first mechanism as direct charge-injection type (DCI-type) and the second one as energy-transfer type (ET-type). In order to determine the work mechanism in inverted QD-LEDs, the following two demands must be met: (1) the EL must only originates from QDs; (2) the DCI and ET processes can be separately probed, i.e., a delicate design of the QD-LEDs should be implemented to preclude the involvement of these two processes.


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 schematic work mechanism in QD-LEDs, direct charge-injection (left) and energy-transfer (right). charges injection into QDs,  electrons injection into HTL, and  energy transfer from HTL molecules to QDs.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: The schematic work mechanism in QD-LEDs, direct charge-injection (left) and energy-transfer (right). charges injection into QDs, electrons injection into HTL, and energy transfer from HTL molecules to QDs.
Mentions: As is well-known, there are two mechanisms proposed to explain the EL processes in QD-LEDs111213. For the first one, carriers transported through charge-transport layers are directly injected into QDs, where they can form excitons that then can radiatively recombine, as shown in Fig. 1 (left panel). The second one depends on the ability to form excitons on the organic molecules surrounding the QD film that then resonantly transfer the exciton energy to QDs. This work mechanism is schematically shown in Fig. 1 (right panel). Hereafter, we refer to the first mechanism as direct charge-injection type (DCI-type) and the second one as energy-transfer type (ET-type). In order to determine the work mechanism in inverted QD-LEDs, the following two demands must be met: (1) the EL must only originates from QDs; (2) the DCI and ET processes can be separately probed, i.e., a delicate design of the QD-LEDs should be implemented to preclude the involvement of these two processes.

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.