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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 left panel represents the EL spectra of QD-LEDs at the operating voltage of 4.5 V. All the EL spectra are shown in a half-exponential coordinates to clearly exhibit EL components; the right panel represents the image of Device B driven under operating voltage of 3.0 V.
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f4: The left panel represents the EL spectra of QD-LEDs at the operating voltage of 4.5 V. All the EL spectra are shown in a half-exponential coordinates to clearly exhibit EL components; the right panel represents the image of Device B driven under operating voltage of 3.0 V.

Mentions: Figure 4 depicts the EL spectra of the QD-LEDs with and without FIrpic layer at an operation voltage of 5 V. Half-exponential coordinates are adopted to clearly exhibit EL components. We can see that the parasitic EL emission from the adjacent organic layers, which commonly occurs in QD-LEDs2, is not observed in our QD-LEDs. The pure QD emission at a peak wavelength of 605 nm with a FWHM of 42 nm illustrates the highly efficient radiative recombination of excitons in the QDs. Moreover, there is not any broadening feature or emission at the low-energy region in the EL spectra for each device, implying absence of emission from deep-level trap states. The EL peak wavelength is red-shifted (~3 nm) relative to the PL emission measured in toluene solution, which may be owing to the dot-to-dot interaction (e.g., Föster resonant energy transfer) in close packed solid films and the Stark effect induced by electric field. All of the results imply that the excitons are dominantly formed on QDs by the DCI 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 left panel represents the EL spectra of QD-LEDs at the operating voltage of 4.5 V. All the EL spectra are shown in a half-exponential coordinates to clearly exhibit EL components; the right panel represents the image of Device B driven under operating voltage of 3.0 V.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: The left panel represents the EL spectra of QD-LEDs at the operating voltage of 4.5 V. All the EL spectra are shown in a half-exponential coordinates to clearly exhibit EL components; the right panel represents the image of Device B driven under operating voltage of 3.0 V.
Mentions: Figure 4 depicts the EL spectra of the QD-LEDs with and without FIrpic layer at an operation voltage of 5 V. Half-exponential coordinates are adopted to clearly exhibit EL components. We can see that the parasitic EL emission from the adjacent organic layers, which commonly occurs in QD-LEDs2, is not observed in our QD-LEDs. The pure QD emission at a peak wavelength of 605 nm with a FWHM of 42 nm illustrates the highly efficient radiative recombination of excitons in the QDs. Moreover, there is not any broadening feature or emission at the low-energy region in the EL spectra for each device, implying absence of emission from deep-level trap states. The EL peak wavelength is red-shifted (~3 nm) relative to the PL emission measured in toluene solution, which may be owing to the dot-to-dot interaction (e.g., Föster resonant energy transfer) in close packed solid films and the Stark effect induced by electric field. All of the results imply that the excitons are dominantly formed on QDs by the DCI 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.