Scientists go deep to quantify perovskite properties

Rice University, Los Alamos lead project to study excitons important to next-generation electronics.


Led by Rice University and Los Alamos National Laboratory, a recent study offers new insights on electronic properties in quantum-scale devices that are likely to impact the growing field of low-cost perovskite-based optoelectronics. Scientists studied the behavior of excitons trapped in quantum wells made of crystalline, halide-based perovskite compounds.

Scientists also created a scale to determine the binding energy of excitons, and along these lines the band gap structures, in perovskite quantum wells of any thickness. This could thus help in the essential design of cutting-edge semiconductor materials.

Perovskite quantum well-based optoelectronic devices convert and control light at the quantum scale, reactions below 100 nanometers that follow different rules from those dictated by classical mechanics. Scientists suggest that any step toward maximizing their efficiency will have a wide impact.

Los Alamos scientists Aditya Mohite said, “Understanding the nature of excitons and generating a general scaling law for exciton binding energy is the first fundamental step required for the design of any optoelectronic device, such as solar cells, lasers or detectors.

In the previous study, scientists discovered that they could tune the resonance of excitons and free carriers inside RPP perovskite layers by changing their atomic thickness. That seemed to change the mass of the excitons, yet researchers couldn’t quantify the phenomenon as of not long ago.

Increasing the thickness of these semiconductors offers a fundamental understanding of the quasi-dimensional, intermediate physics between monolayer 2D materials and 3D materials.

Scientists later tested the wells under a 60-tesla magnetic field to directly probe the effective mass of the excitons, a characteristic that is key for both modelings of the excitons and understanding energy transport in the 2D perovskite materials. They then exposed the samples to ultra-low temperatures, high magnetic fields, and polarized light.

Scientists later send the samples for optical spectroscopy to offer a direct probe of the optical transitions within the RPPs to derive the exciton binding energies, which is the basis of the breakthrough exciton scaling law with quantum well thickness.

Matching their results to the computational model designed by Jacky Even, a professor of physics at INSA Rennes, France, the scientists verified that the compelling mass of the excitons in perovskite quantum wells up to five layers is around two times larger than in their 3D mass partner.

Lead author Blancon, currently a research scientist at Los Alamos said, “As they approached five layers (3.1 nanometers), the binding energy between electrons and holes was significantly reduced but still larger than 100 milli-electron volts, making them robust enough to exploit at room temperature. For example, that would allow for the design of efficient light-emitting devices with color tunability.”

The combined experimental and computer model data allowed them to create a scale that predicts exciton binding energy in 2D or 3D perovskites of any thickness. The researchers found that perovskite quantum wells above 20 atoms thick (about 12 nanometers) transitioned from quantum exciton to classical free-carrier rules normally seen in 3D perovskites at room temperature.

Co-author and physicist Junichiro Kono said, “This was a great opportunity for us to demonstrate the unique capabilities of RAMBO for use in high-impact materials research. With excellent optical access, this mini-coil-based pulsed magnet system allows us to perform various types of optical spectroscopy experiments in high magnetic fields up to 30 tesla.”

Mohite said, “This work represents a fundamental and nonintuitive result where we determine a universal scaling behavior for exciton binding energies in Ruddlesden-Popper 2D hybrid perovskites. This is a fundamental measurement that has remained elusive for several decades, but its knowledge is critical before the design of any optoelectronic devices based on this class of materials and may have implication in the future for design of, for example, zero-threshold laser diodes and multifunctional hetero-material for optoelectronics.”

Additional co-authors of the paper are Rice graduate student Hsinhan Tsai, also of Los Alamos; Fumiya Katsutani and Timothy Noe of Rice; Wanyi Nie, Sergei Tretiak, Scott Crooker and Jared Crochet of Los Alamos; Constantinos Stoumpos of Northwestern University; and Boubacar Traore, Laurent Pedesseau, Mikael Kepenekian and Claudine Katan of the University of Rennes, France. Kanatzidis is the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern. Kono is a professor of electrical and computer engineering, of physics and astronomy and of materials science and nanoengineering.

The paper describing the study is published in the journal Nature Communications paper.

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