A New Approach to Reducing Dynamic Disorder in Perovskite Nanocrystals

According to a study published in Nature Communications on July 24^th, 2024, the College of Engineering at Seoul National University announced that a research team led by Professor Tae-Woo Lee from Seoul National University’s Department of Materials Science and Engineering, in collaboration with Professor Andrew M. Rappe of the University of Pennsylvania, created an ultra-high efficiency perovskite nanocrystal light-emitting diodes.

This was accomplished by strengthening the perovskite lattice while inhibiting the material's natural low-frequency dynamics.

Background

Perovskite is a semiconductor material made up of cube-shaped nanocrystals containing organic cations, metal cations, and halogens. Due to their high color purity, tuneability, and cost-effectiveness, perovskite light emitters have gained popularity as possible next-generation emitters.

Prior to 2014, perovskites were largely employed in solar cells since their luminescence was not bright enough to be seen at ambient temperature. Despite this restriction, Professor Tae-Woo Lee identified perovskite’s promise as a next-generation emitter early on and acquired a portfolio of foundational patents for perovskite light-emitting materials in 2014.

Furthermore, in 2015, his team produced the first study report proving the improvement of efficiency in perovskite LEDs from 0.1% to 8.53%, which is equivalent to the level of phosphorescent OLEDs. This breakthrough has prompted researchers throughout the world to do extensive and in-depth studies on enhancing the efficiency of perovskite emitters studies

As a pioneer in this field, Professor Lee’s team advanced perovskite self-emissive devices in 2022, attaining an external quantum efficiency (EQE) of 28.9% (almost theoretical maximum), peak brightness of 470,000 nits, and an operating lifespan of up to 30,000 hours.

Moving closer to commercialization, Professor Lee’s startup business, SN Display Co. Ltd., displayed TV and tablet display prototypes at the CES (Consumer Electronics Show) in 2022 and 2023, which drew a lot of attention from industry professionals.

However, the study team recognized the need to address a crucial challenge: the drop in luminescence efficiency caused by the perovskite’s intrinsic ionic nature. Perovskite materials, unlike standard inorganic semiconductors, are made up of weak ionic bonds, and large amplitude displacement of atoms in their crystal lattices can result in dynamic disorder.

This dynamic disorder disrupts the radiative recombination process in perovskite materials, resulting in exciton dissociation and lower luminescence efficiency. Despite the need to overcome this fundamental restriction, little research has been conducted on how dynamic disorder influences the luminous characteristics of perovskites and ways to improve efficiency by minimizing it.

Achievements

Professor Tae-Woo Lee’s team, in collaboration with Professor Andrew M. Rappe of the University of Pennsylvania in the United States and Professor Omer Yaffe of the Weizmann Institute of Science in Israel, proposed a novel mechanism for increasing the luminescence efficiency of perovskite emitters by incorporating conjugated molecular multipods (CMMs).

The process is that the lattice is reinforced when CMM attaches to its surface, which suppresses low-frequency dynamics and lowers dynamic disorder in the lattice. Ultimately, this resulted in increased luminescence efficiency for perovskite materials.

A notable accomplishment is the development of ultra-high-efficiency LEDs with a 26.1% EQE. This value, which is among the highest in perovskite nanocrystal LED efficiency, is particularly noteworthy because it was attained by improving the material’s intrinsic emission efficiency rather than by designing the device structure to increase light outcoupling efficiency.

Expected Effects

It is acknowledged that Professor Lee's team's perovskite emitters have great promise for use as next-generation display emitters. Because green makes up the majority of the color standard for ultra-high-definition screens in Rec. 2020, developing high-color purity and high-efficiency green emitters is crucial to the development of new display technologies.

The study team's LEDs have electroluminescence wavelengths almost identical to the Rec. 2020 standard's main green hue. This innovation is anticipated to accelerate the commercialization of next-generation screens dramatically.

This research presents a new material-based approach to overcoming the intrinsic limitations of perovskite light emitters. We anticipate that this will significantly contribute to the development of high-efficiency, long-lifetime perovskite light-emitting devices and the commercialization of next-generation displays.

Tae-Woo Lee, Professor, Seoul National University

Professor Andrew M. Rappe added, “Together we have shown the power of molecules in strengthening perovskites and making them better light emitters. By combining the powers of molecular chemistry, physics, mechanics, and optics, we are inventing new materials to lead us into a bright and energy-efficient future.”

Introduction to the Research Team

Dong-Hyeok Kim, the study’s lead author, is a PhD candidate at Seoul National University's Department of Materials Science and Engineering. His research focuses on creating next-generation perovskite light emitters.

Dr. Seung-Je Woo, a Marie-Curie Fellow at the Cavendish Laboratory at the University of Cambridge, researches optoelectronic materials with ultrafast laser spectroscopy.

Dr. Claudia Pereyra Heulmo of the University of Pennsylvania is presently researching optoelectronics at the University of the Republic in Montevideo, Uruguay. Dr. Min-Ho Park is an assistant professor in the Department of Materials Science and Engineering at Soongsil University, having previously completed postdoctoral research at Seoul National University and worked at Samsung Display.

The study was supported by the Research Leader Program and Outstanding Researcher Exchange Support (BrainLink) program promoted by the Ministry of Science and ICT (MSIT) and National Research Foundation of Korea (NRF) and the National Science Foundation of the USA, as part of the IMOD Science and Technology Center.

Journal Reference:

Kim, D.-H., et al. (2024) Surface-binding molecular multipods strengthen the halide perovskite lattice and boost luminescence. Nature Communications. doi.org/10.1038/s41467-024-49751-7.