Compared with Cd-based QDs, InP-based QDs have lower photoluminescence quantum yields (PL QYs) and broader full-width at half-maximum (FWHM). In particular, bare InP core has extremely low PL QY (＜1%) due to the ease of oxidation of their highly reactive surface even in insert reaction chambers. It has been reported that the defects from oxidative species are probably the reasons for the non-radiative recombination and poor PL QY of these materials. Over the last decade, extensive studies have been conducted to improve the optoelectronic properties of InP-based QDs for display and lighting applications, such as growing shell or adding HF before shell growth. However, HF has serious corrosivity and toxicity, and the rapidly increased pressure when injecting HF at high temperature. Therefore, a safe and easy synthesis strategy is necessary for growing high-quality InP-based QDs.
The Solution: A group of Chinese scientists from Key Laboratory for Special Functional Materials of Ministry of Education, National & Local Joint Engineering Research Center for High-efficiency Display and Lighting Technology proposed a fluoride-free synthesis strategy to in-situ passivate the InP cores, in which zinc myristate reacted with phosphine dangling bonds to form Zn-P protective layer and protect InP cores from the water and oxygen in the environment.
The Result: InP/ZnSe/ZnS core/shell QDs with high PL QY and its corresponding high-brightness green InP-based QLEDs.
-High PL QY and narrow FWHM of InP/ZnSe/ZnS QDs: PL QY=91%, FWHM=44 nm
-High luminance of QLEDs: 175,084 cd m-2
-Long operational lifetime of QLEDs: T50@100 cd m-2 lifetime of more than 20,000 h
The Future: To realize the commercialization of full-color environmentally friendly QLED technology, the performance of green InP-based devices still requires further effort by researchers, such as exploring new synthesis methods of InP QDs, exploring the luminescence mechanism of QLEDs and exploring new structures of QLEDs.
Prof. Fei Chen and Zhenghui Wu mentioned: "With the acceleration of the commercialization of QDs in terms of display and lighting, the performance enhancement of environmentally friendly QDs and corresponding electroluminescent devices has become an urgent task. To realize the commercialization of full-color environmentally friendly QLED technology, the performance of green InP-based devices still requires further effort by researchers. We demonstrated a strategy to in-situ passivate the InP cores, in which zinc myristate reacted with P dangling bonds to form Zn-P protective layer and protect InP cores from the water and oxygen in the environment. This proposed a safe and easy operating route for high-performance green InP-based devices."
The Impact: These advancements provide a new idea for improving green InP based QDs and corresponding QLEDs, ultimately accelerating the commercialization process of environmentally friendly full color QLEDs without heavy metals.
The research has been recently published in the online edition of Materials Futures, a prominent international journal in the field of interdisciplinary materials science research.
Reference:
Yuanbin Cheng, Qian Li, Mengyuan Chen, Fei Chen, Zhenghui Wu and Huaibin Shen "High-brightness green InP-based QLEDs enabled by in-situ passivating core surface with zinc myristate."
https://doi.org/10.1088/2752-5724/ad3a83
