Lead halide perovskites are a class of materials that have shown great promise for use in solar panels, semiconductors, LEDs and other optoelectronic devices.
One of the most impressive features of these materials is their long electron-hole recombination time—simply, the time it takes a high-energy electron in the material’s conduction band (where the electron conducts electricity) to fall back into a vacant spot in the valence band (where the electron “resides”).
This long recombination time is key factor in making devices more efficient. However, despite extensive theoretical and experimental study, until now researchers haven’t fully understood why it happens.
In a paper published Sept. 24, 2025, in the journal Physical Review Letters, a multi-institutional team led by Yuan Ping, an associate professor of materials science and engineering at the University of Wisconsin-Madison, lays out a new theory and computational technique that explains why electrons and holes in lead halide perovskites take so long to recombine.
Ping and her students develop new quantum theory and computational methods to describe the physical properties of materials. In this research, says Andrew Grieder, a PhD student in Ping’s lab and first author on the paper, the team needed to strike a balance between an acceptable level of theoretical accuracy and the reality of simulating a large physical system that includes, for example, grain boundaries.
“Our method provides a new tool in materials engineering, which enables the direct simulation of microstructures, low-symmetry materials, grain boundaries and disorder, while including quantum descriptions of electron dynamics,” he says. “This goes far beyond standard parameterized classical mechanics simulations.”
The team’s new tool combines machine learning force fields—which predict how atoms move in solids—and a physically informed “tight binding model” that allows the researchers to accurately reproduce complex quantum behaviors using only atomic positions. As a result, it provides quantum-level accuracy at much larger time and length scales than traditional methods—making it possible to study complex materials and processes that were previously out of reach.
Enter the lead halide perovskite. To resolve the disagreement about the mechanism that leads to long electron hole recombination times, Ping, Grieder and their collaborators in academia and at national laboratories used their method to study cesium lead bromide, a perovskite material known for its superior optoelectronic properties.
They found that spontaneous structural changes in the perovskite material can create conditions that naturally keep charges apart. At low temperatures, the perovskite material forms tiny regions, or nano-domains, with special boundaries that have built-in electric direction, or polarization. Those polarized boundaries push the electrons and the holes in opposite directions, preventing them from recombining quickly. That separation helps to explain the material’s excellent performance—particularly in cold conditions, when electrons and holes tend to “hop” from place to place, aided by vibrations, called phonons, in the material. Conversely, higher temperatures cause the built-in polarization to fade, which in turn affects the material’s efficiency.
“This result provides an explanation of why electrons and holes take so long to recombine in this class of materials,” says Ping. “Without the large scale and quantum description, these simulations would not have captured these effects.”
Even more broadly, the team’s work significantly improves how researchers can simulate and study materials at the nanoscale level. “The results from this study highlight the promise of this method in aiding new discoveries related to electron transport and dynamics in microstructures, low-symmetry materials, grain boundaries, and disorder,” says Grieder. “Given the generality of the method, it can be applied to a wide class of problems related to materials science engineering and help pave the way to better materials for future (opto)-electronics.”
Other authors on the paper include Marcos Calegari Andrade, University of California, Santa Cruz, and Lawrence Livermore National Laboratory; Hiroyuki Takenaka, University of California, Santa Cruz; Tadashi Ogitsu, Lawrence Livermore National Laboratory; and Liang Z. Tan, Lawrence Berkeley National Laboratory.
The authors acknowledge support from the Computational Materials Sciences Program funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division for the materials application and development of ab initio tight-binding code. The authors acknowledge support from the computational chemical science program within the Office of Science at DOE under grant No. DE-SC0023301 for the code development of tight-binding-LAMMPS interfaces and parallelization. Part of the materials application and theory validation was supported by NSF under grant No. CHE-2203633. Additional support for data analysis and interpretation was provided by user program of the Molecular Foundry, Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Top photo caption: Yuan Ping, her PhD student Andrew Grieder, and their collaborators have developed both new theory and a computational technique that explains why electrons and holes in lead halide perovskites take so long to recombine. The perovskites are a class of materials that are promising for solar panels, semiconductors, LEDs and other optoelectronic devices, and a long recombination time is a key factor in their high efficiency. Photo: Joel Hallberg.