Great thanks for reading this.
The CuO, MoO3, V2O5 are usually served as hole injection layers (HIL) in OLED/QLED. Generally, MoO3, V2O5, these two materials have been seen as natural n-type conductivity. CuO is p-type. So, how did the carrier type of HIL influence the OLED/QLED device charge transport? Or If the material with proper VBM (usually lower), it can serve as HIL, while the carrier type is not important?
The energy alignments to the contact layers of metal oxides determine the device structures whether metal oxides are p-type or n-type. The defects or impurities of metal oxides play important role to their charge transport properties. Furthermore, the contacts between metal oxides and organic semiconductors could lead to some interactions. The electrical driven devices can lead to some electrochemical reaction too. There are some refetences you could find online easily to explain in details.
The work function of hole or electron transport/injection layers matters. Keep in mind that the valance band maximum (ionization potential) is the fundamental property of a material. However, the work function is defined by the position of the Fermi level and thus can be different for the same material depending on the deposition or doping conditions. The type of conductivity does not matter. In terms of injection, there is no fundamental difference between holes and electrons. The injection of a hole could be considered as the extraction of an electron and vice versa.
You may refer to the paper of Greiner, M. T. et al., Universal energy-level alignment of molecules on metal oxides. Nat. Mater. 11, 76-81 (2012).
Dear Jingrui Ma ,
hope you are well!
In the light emitting diode where the active material is intrinsic, one has to supply such material with two injecting layers where one injects electrons and the other injects hole. The electron injection will be accomplished by injecting electrons from the conduction band of the EIL to the conduction band active layer. This means that the EIL must be n-type containing electron majority.
As for the HIL., if the holes are injected from the valence band of the HIL into the valence band of the i-layer, then the HIL must be p-type.
If the holes are injected from the conduction band of the HIL to the valence band of the i-layer then the material can be n-type provided the its Femilevel lies under the valence band edge.
Best wishes
Xuhua Wang Thanks a lot. The energy alignments determine the device structure and the defects or impurities of metal oxides play an important role in their charge transport properties. I read the related reports and the band edge location is more important to determine whether the materials can serve as HIL. Thanks again.
Viktor Brus One more question. The transport layer may be not the same conductivity as the function, if the ETL with the higher VBM close to the EML CBM?
Abdelhalim abdelnaby Zekry Prof. Abdelhalim abdelnaby Zekry, your comment also help me a lot. Great thanks!
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