Solar cell efficiency has seen remarkable progress in recent years thanks to light-harvesting materials such as halide perovskites. Nevertheless, the reliable large-scale production of these materials remains a significant challenge.
A process developed by Rice engineers and collaborators yields 2D halide perovskite crystal layers of ideal thickness and purity through dynamic control of the crystallization process ⎯ a key step toward ensuring device stability for optoelectronics and photovoltaics. Image Credit: Jeff Fitlow/Rice University.
A method developed by Aditya Mohite, a chemical and biomolecular engineer at Rice University, in collaboration with researchers from Northwestern University, the University of Pennsylvania, and the University of Rennes, addresses this challenge. The process involves controlling the temperature and duration of the crystallization process to obtain 2D perovskite-based semiconductor layers with ideal thickness and purity.
This process, referred to as "kinetically controlled space confinement," holds the potential to enhance the stability and reduce the cost of emerging technologies that rely on halide perovskites, such as optoelectronics and photovoltaics.
Producing 2D perovskite crystals with layer thicknesses ⎯ or quantum well thickness, also known as ‘n value’⎯ greater than two is a major bottleneck. An n value higher than four means materials have a narrower band gap and higher electrical conductivity ⎯ a crucial factor for application in electronic devices.
Jin Hou, Study Lead Author and PhD Student, George R. Brown School of Engineering, Rice University
The study was published in Nature Synthesis.
When atoms or molecules come together to form crystals, they organize themselves into highly ordered and regular lattices. For instance, ice can exist in 18 distinct atomic arrangements, or phases. Similarly, the constituents of halide perovskites can adopt various lattice arrangements. Given that the properties of materials depend on their phase, scientists strive to produce 2D halide perovskite layers that maintain a single phase consistently.
However, traditional synthesis techniques for higher n value 2D perovskites tend to result in uneven crystal growth, which can adversely affect the material's performance and reliability.
In traditional methods of 2D perovskite synthesis, you get crystals with mixed phases due to the lack of control over crystallization kinetics, which is basically the dynamic interplay between temperature and time. We designed a way to slow down the crystallization and tune each kinetics parameter gradually to hit the sweet spot for phase-pure synthesis.
Jin Hou, Study Lead Author and PhD Student, George R. Brown School of Engineering, Rice University
In addition to developing a synthesis method capable of achieving a gradual increase in the n value in 2D halide perovskites, the researchers also constructed a comprehensive map, often referred to as a phase diagram, of the entire process. They accomplished this through characterization, optical spectroscopy, and the application of machine learning techniques.
“This work pushes the boundaries of higher quantum well 2D perovskites synthesis, making them a viable and stable option for a variety of applications,” Hou added.
“We have developed a new method to improve the purity of the crystals and resolved a long-standing question in the field on how to approach high n value, phase-pure crystal synthesis,” adds Mohite, an associate professor of chemical and biomolecular engineering and materials science and nanoengineering has played a pivotal role in advancing the quality and performance of halide perovskite semiconductors.
His lab has been at the forefront of developing diverse techniques, ranging from optimizing the initial stage of crystallization to refining solvent design.
“This research breakthrough is critical for the synthesis of 2D perovskites, which hold the key to achieving commercially relevant stability for solar cells and for many other optoelectronic device applications and fundamental light matter interactions,” Mohite noted.
This research received support from various sources, including Rice University startup funds within the molecular nanotechnology initiative, the Department of Energy's Office of Energy Efficiency and Renewable Energy (2022-1652) and its Office of Science (DE-SC0012704), the Army Research Office (W911NF2210158, W911NF1910109), the China Scholarships Council (202107990007).
The National Science Foundation (2025633, 1920248) and its Graduate Research Fellowship Program, the Office of Naval Research (N000142012725), Northwestern University, the Alfred P. Sloan Foundation, the Swiss National Science Foundation (P2ELP2_187977), Institut Universitaire de France, and the European Union's Horizon 2020 (861985) also provided funding for this study.
Journal Reference:
Hou, J., et al. (2023). Synthesis of 2D perovskite crystals via progressive transformation of quantum well thickness. Nature Synthesis. doi.org/10.1038/s44160-023-00422-3.