Purdue researchers have developed a novel approach to realize extremely efficient light emitters and lasers that combines the benefits of both aggregated and single-molecule states within a 2D hybrid perovskite superlattice. 

Organic-inorganic hybrid perovskites are semiconducting materials that are a promising option for the future oflighting and power generation. Traditionally, organic luminescent molecules are used either as closely packed aggregates or as single molecules diluted within another matrix. While this model has garnered significant research interest, the behavior of these molecules in a loosely confined space remains poorly understood. 

Published in Nature, Letian Dou, Charles Davidson Associate Professor of Chemical Engineering, Brett Savoie, Coyle Mission Collegiate Professor of Engineering at the University of Notre Dame, and Kang Wang, a former Purdue postdoctoral researcher, collaborated with international researchers to discover a new phase of molecular aggregate that forms in a two-dimensional (2D) hybrid perovskite superlattice with a near-equilibrium spacing, referred to as a "single-molecule-like aggregate" (SMA). In this phase, the molecular emitters are held in proximity (i.e., within 1 nanometer [10^-9 meter] range from each other) but surprisingly remain electronically isolated with minimized electronic interference from neighboring molecules.

This novel structure combines the advantages of both single molecules and molecular aggregates, leveraging molecular interactions for optimized performance. On one hand, the tightly packed molecules behave like individual entities, resulting in highly efficient light emission with near unity efficiency. On the other hand, their precise arrangement and close proximity also form pseudo-clusters, significantly enhancing light manipulation and lasing efficiency. Through computer simulations and structural analysis, researchers determined that the distinct properties of this arrangement are largely driven by the internal rotational and vibrational dynamics of the molecules within the lattice. 

“This hybrid superlattice defines a rich family of optoelectronic materials that can be achieved by rationally designing organic emitters with desirable properties.” Wang said “More importantly, the SMA confined within perovskite 2D superlattices go beyond the current classification of organic matter, such as typical H-, J-, or null aggregates, representing a previously undiscovered phase at a near-equilibrium distance.”

“The mechanism that we’ve discovered for SMA formation is very general. This means that this is just the start of designing new semiconductors that leverage SMA functionality.” Savoie said.

As a proof-of-concept demonstration, the team showed that a light emitting diode using this new material can operate 50 times more efficiently than the same molecules without the perovskite sublattice. The lasing performance obtained from this material also surpasses most of the well-established organic and perovskite systems reported in the literature. The team is currently looking into improving the materials and device fabrication procedures to achieve even more efficient LEDs and lasers for practical applications.

“This study creates new opportunities for understanding how to improve efficiency in light-emitting devices, opening doors for researchers to drive innovation in advanced spectroscopic and photonic material design and performance. This is just a start, and I’m sure this conceptual breakthrough will have long-lasting impact on the development of efficient light-emitting materials and devices in the future” Dou said.

Additional collaborators on this work include Zih-Yu Lin, Wenhao Shao, Yuanhao Tang, Dharini Varadharajan, Hanjun Yang, Angana De, Colton B. Fruhling, Alexandra Boltasseva, and Vladimir M. Shalaev from Purdue University; Zehua He and Yong Sheng Zhao from the Institute of Chemistry, Chinese Academy of Sciences; Conrad A. Kocoj and Peijun Guo from Yale University; and Aidan H. Coffey and Chenhui Zhu from Lawrence Berkeley National Laboratory.