Double-type-I charge-injection heterostructure for quantum-dot light-emitting diodes

Enforcing balanced electron-hole injection into the emitter layer of quantum-dot light-emitting diodes (QLEDs) remains key to maximizing the quantum efficiency over a wide current density range. This was previously thought not possible for quantum dot (QD) emitters because of their very deep energy...

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Bibliographic Details
Published in:Materials horizons 2022-08, Vol.9 (8), p.2147-2159
Main Authors: Wang, Li-Xi, Tang, Cindy G, Tan, Zhao-Siu, Phua, Hao-Yu, Chen, Jing, Lei, Wei, Png, Rui-Qi, Chua, Lay-Lay, Ho, Peter K. H
Format: Article
Language:English
Subjects:
Charge injection
Current density
Emitters
Energy bands
Heterostructures
Light emitting diodes
Nanoparticles
Organic semiconductors
Quantum dots
Quantum efficiency
Semiconductors
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Summary:Enforcing balanced electron-hole injection into the emitter layer of quantum-dot light-emitting diodes (QLEDs) remains key to maximizing the quantum efficiency over a wide current density range. This was previously thought not possible for quantum dot (QD) emitters because of their very deep energy bands. Here, we show using Mesolight® blue-emitting CdZnSeS/ZnS QDs as a model that its valence levels are in fact considerably shallower than the corresponding band maximum of the bulk semiconductor, which makes the ideal double-type-I injection/confinement heterostructure accessible using a variety of polymer organic semiconductors as transport and injection layers. We demonstrate flat external quantum efficiency characteristics that indicate near perfect recombination within the QD layer over several decades of current density from the onset of device turn-on of about 10 μA cm −2 , for both normal and inverted QLED architectures. We also demonstrate that these organic semiconductors do not chemically degrade the QDs, unlike the usual ZnMgO nanoparticles. However, these more efficient injection heterostructures expose a new vulnerability of the QDs to in device electrochemical degradation. The work here opens a clear path towards next-generation ultra-high-performance, all-solution-processed QLEDs. Enforcing balanced electron-hole injection into the emitter layer of quantum-dot light-emitting diodes through a double-type-I heterostructure using polymer semiconductors maximizes the quantum efficiency over a wide current density range.
ISSN:2051-6347
2051-6355
DOI:10.1039/d1mh00859e