Strengthening lattices, yields ultra-high efficiency in Perovskite LEDs

Strengthening lattices, yields ultra-high efficiency in Perovskite LEDs
by Riko Seibo
Tokyo, Japan (SPX) Sep 01, 2024

The College of Engineering at Seoul National University has announced a significant advancement in the development of ultra-high efficiency perovskite nanocrystal light-emitting diodes (LEDs). This achievement was made possible by a research team led by Professor Tae-Woo Lee from the Department of Materials Science and Engineering at Seoul National University, in collaboration with Professor Andrew M. Rappe of the University of Pennsylvania. Their work involved reinforcing the perovskite lattice and mitigating the material's natural low-frequency dynamics. The findings were published in the journal 'Nature Communications' on July 24.

Perovskite, a semiconductor material composed of cube-shaped nanocrystals, includes organic cations, metal cations, and halogen elements. It has been recognized for its potential as a next-generation light emitter due to its superior color purity, tunability, and cost-efficiency.

Before 2014, perovskites were mainly used in solar cells, as their luminescence was insufficient for visibility at room temperature. However, Professor Tae-Woo Lee saw the potential of perovskites as future emitters and secured essential patents for perovskite light-emitting materials in 2014. By 2015, his team had increased the efficiency of perovskite LEDs from 0.1% to 8.53%, bringing it in line with phosphorescent OLEDs. This breakthrough spurred global research into enhancing the efficiency of perovskite emitters.

Professor Lee's team continued to lead in this area, achieving a near-theoretical maximum external quantum efficiency (EQE) of 28.9% in 2022, along with a peak brightness of 470,000 nits and an operational lifespan of up to 30,000 hours. To further commercialize this technology, Professor Lee's startup, SN Display Co. Ltd., showcased prototypes at the CES in 2022 and 2023.

The team identified a critical challenge in the reduction of luminescence efficiency due to the ionic nature of perovskite. The weak ionic bonds in perovskite materials can cause large-amplitude displacement of atoms within the crystal lattice, resulting in dynamic disorder that interferes with the radiative recombination process, leading to exciton dissociation and decreased luminescence efficiency. Addressing this issue, however, has been underexplored until now.

In collaboration with Professor Andrew M. Rappe and Professor Omer Yaffe of the Weizmann Institute of Science, Professor Lee's team proposed a novel mechanism to enhance the luminescence efficiency of perovskite emitters by incorporating conjugated molecular multipods (CMMs). These CMMs bind to the perovskite lattice, strengthening it and reducing dynamic disorder, which in turn improves the luminescence efficiency.

This work resulted in the creation of ultra-high-efficiency LEDs with an EQE of 26.1%, one of the highest efficiencies recorded in perovskite nanocrystal LEDs. Notably, this improvement was achieved by enhancing the material's intrinsic emission efficiency rather than altering the device structure to boost light outcoupling efficiency.

The perovskite emitters developed by Professor Lee's team hold great promise as future display technologies. Given that green is a critical color in the Rec. 2020 standard for ultra-high-definition displays, achieving high-efficiency green emitters is crucial. The LEDs created by the team emit light at wavelengths close to the green primary color in the Rec. 2020 standard, potentially accelerating the development of next-generation displays.

Professor Tae-Woo Lee remarked, "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."

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."

The lead author of this study, Dong-Hyeok Kim, is a PhD candidate at Seoul National University, focusing on next-generation perovskite light emitters. Dr. Seung-Je Woo, a Marie-Curie Fellow at the University of Cambridge, is researching optoelectronic materials using ultrafast laser spectroscopy. Dr. Claudia Pereyra Heulmo, from the University of Pennsylvania, is currently investigating optoelectronics at the University of the Republic in Montevideo, Uruguay. Dr. Min-Ho Park, after postdoctoral research at Seoul National University and work at Samsung Display, is now an assistant professor at Soongsil University.

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

Research Report:Surface-binding molecular multipods strengthen the halide perovskite lattice and boost luminescence