Speaker
Description
Colloidal quantum dots (QDs)-based light-emitting diodes (QD-LEDs) has been actively researched due to the potential impacts to the display and lighting industry base on the unique properties of QDs itself such as size-dependent bandgap tune ability, narrow emission spectrum, and low-cost solution-based processing.
Introduction
Indiumphosphide (InP) based quantum dot (QDs) has been considered as an environmentally friendly alternative to Cd-based QDs due to their promising photoluminescent (PL) and electroluminescent (EL) properties and potential for the display market. Here, the research efforts on improving the efficiency and stability of InP EL-QD-LED and the remained challenges of PL applications will presented including current investigations. Our broad understanding of the design approach InP QD materials can provide new opportunities to overcome the remained research issues for the commercialization of QDs in the next-generation information display market. Since the inkjet printing technology for patterning of QD layers is essential for the full-colour display applications, we will also present the related activities.
Green and red InP QD-LEDs
InP-based QDs have been identified as one of the most promising materials for green and red emission in displays. The high and stable QY of InP-based QDs can be accomplished by controlling the confinement of electron and hole wave functions under the electric field and the charged conditions in the device in order to have high EQE of QD-LEDs. The alloyed QD core structure would be the favourable QD design for efficient EL devices because it can provide a smoothed quantum confinement in the core, which minimizes Auger quenching. The confined electron and hole wave functions in the core and additional proper shell design i.e. optimized thickness and materials will reduce the exciton polarization under the applied electric field and provide the effective passivation of particles. InP-based inverted device has been experienced the lack of efficient electron injection into the conduction band minimum (CBM) of the InP-based QDs due to the higher energy off-set from the CBM of ZnO nanoparticle (NP) electron transport layers (ETLs). Therefore, the Mg-doped ZnO (i.e. ZnMgO) NPs which has the higher CBM as compared to the ZnO NPs are often used the alternative ETLs. In this research, a ZnO/ZnMgO bilayer was utilized as the ETL in order to improve the electron injection into the synthesized red InPZnSeS/ZnSe/ZnS QDs.
QD-LED Printing
Green and red InP/ZnSe/ZnS QDs and blue ZnSeTe/ZnSe QDs were sophisticatedly designed for application in QD-LEDs by optimizing different precursor, shell thickness, and organic surface ligands. Optimizing charge carrier balance and the recombination zone in the multi-layered device structure is key for the development of highly efficient and stable InP-based QLEDs. Developing high-performance QD-LEDs based on InP-based QDs is quite important to bring QD-LEDs into the future market. Our results show that InP/ZnSe/ZnS QDs and blue ZnSeTe/ZnSe QDs are the most promising candidates for the Cd-free QD-LEDs considering QY, FWHM and performance in the device. Finally, several layers of such QD-LED structures can be easily ink-jet printed.
Starting from hole injection layers and cross linked HTL the solution-based InP QDs of the three main colors of a RGB-display can be printed. Based on these printing processes, the way paving to a fully ink-jet printed QD-LED display in the near future.
Acknowledgment
The authors would like to thank the Korea government Ministry of Trade, Industry and Energy (MOTIE) for financial support via “2016 Consulting business through utilization of excellent technical manpower in Germany” and funded by European Union’s Horizon 2020 research and innovation programme under grant agreement No. 862410.
References
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| Keywords | Quantum Dot, QD-LED, InP, Ink-Jet Printing |
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