Solid-state NMR spectroscopy evaluates new materials for sustainable optoelectronic technologies to address the global energy crisis

Solar technology can address the need for affordable, practical energy solutions — particularly in remote and off-grid areas where traditional infrastructure is impractical or too costly to deploy. As a renewable resource, solar power produces no direct greenhouse gas emissions, helping to reduce the carbon footprint of energy production. Solar energy also can be harnessed locally, reducing dependence on centralized power plants, imported fossil fuels, and costly transmission infrastructure.

“The current energy crisis underscores the importance of diversifying energy sources,” says Dr. Dominik J. Kubicki, Assistant Professor in the School of Chemistry, University of Birmingham.

“Solar energy, being an abundant and renewable source, presents a valuable alternative to fossil fuels, especially when considering that there are more than eight hundred million people worldwide without access to electricity. It's one of the most significant alternatives available to us, because there is over 1000 times more solar energy hitting the surface of the earth than we need at any given moment.”

Dr. Kubicki’s research uses nuclear magnetic resonance (NMR) spectroscopy to advance solar technology by conducting non-invasive, non-destructive quantitative analytical investigations into the materials used for solar technology.¹ Using NMR to understand the atomic-level structure, dynamic processes, and chemical reactions helps the community tune the structure of solar cell materials, therefore making better-performing and longer-lasting materials.
“My lab develops solar cell materials based on metal halide perovskites and studies their degradation to uncover the underlying chemistry affecting their properties,” he explains. “Mechanosynthesis enables the synthesis of large libraries of materials with diverse structures and properties, while solid-state NMR allows us to examine specific nuclei within a material’s structure. This approach offers quantitative insights that differ from those available through other analytical techniques and play a critical role in understanding how these materials behave, their structure, and how they degrade.”

Dr. Kubicki’s work in solid-state NMR and materials research aims to address the energy crisis by developing advanced solar cell technologies that are efficient, stable, and environmentally friendly. His work currently focuses on halide perovskite solar cells, which hold great promise as a clean energy technology with the potential to provide a more efficient and cost-effective alternative to traditional silicon-based solar cells. Perovskite materials can be tuned to absorb a wide range of wavelengths of light, making them suitable for both traditional rooftop solar panels, and other applications like transparent or flexible solar cells.
“Solid-state NMR helps us understand the atomic-level mechanisms and processes that lead to degradation, enabling us to design better solar cells,” Dr. Kubicki said. “We study structure and dynamics in a variety of materials for light harvesting and emission, broadly classified as metal halide perovskites. Using solid-state NMR, we can access the atomic-level structure, which, together with long-range structural information from diffraction techniques, provides a comprehensive picture of a material. Combining structural information with insights from optical spectroscopies leads to structure-property relationships that help us understand how the performance of a material changes when we modify its structure.”

The team’s research in the field of halide perovskite solar cells could lead to higher efficiencies, lower costs, improvements to stability, and reductions in the use of toxic materials.²³⁴

By using NMR spectroscopy to identify and quantify the chemical species present in perovskite-based optoelectronic devices, Dr. Kubicki’s work aids in understanding the composition of the photoactive component and detecting impurities or by-products that may affect the performance of the solar cell (Figure 1).

“Halide perovskite solar cells have rapidly improved in efficiency over the last decade, though they face stability challenges,” Dr. Kubicki says. “These materials are complex mixtures of chemical elements and additives, making their analysis a challenging task. Solid-state NMR allows us to focus on specific isotopes and understand the behavior of each component within a functioning solar cell.”
NMR can also be used to study the dynamics and mobility of ions within the perovskite structure. This information is essential for understanding charge transport processes, ion migration, and other factors that influence the efficiency and stability of the solar cell. While traditional silicon solar cells guarantee 25 years of operation, halide perovskite solar cells have achieved only about one year of stability thus far. Dr. Kubicki’s work aims to expand the lifespan of halide perovskite solar cells to a decade or more.
“We are currently at the one-year mark, but that’s still fantastic because within five years we have been able to bring stability from days or weeks to over a year,” he explains. “Now we’re working on finding new materials and new ways of stabilizing them. One of the ways we stabilize halide perovskites is by using additives, trying to identify new additives, and understanding what they do to the material that makes it more stable. Understanding the atomic-level microstructure and its relation to properties is essential in this endeavor.”

About Dominik J. Kubicki

Dominik J. Kubicki is an Assistant Professor in the School of Chemistry at the University of Birmingham, UK, and a Visiting Professor in the Department of Physics at the University of Warwick. He graduated from the Warsaw University of Technology, Poland in 2013 and completed his PhD at EPFL, Switzerland in 2018. He held a Marie Curie-Skłodowska Fellowship at the University of Cambridge, UK from 2018 to 2021. In 2022, he received an ERC Starting Grant underwritten by UK Research and Innovation to develop new atomic-level strategies to study perovskite solar cells. His research focuses on new materials for sustainable optoelectronic technologies and benefits from the unique capabilities of the UK High-Field Solid-State NMR Facility at Warwick.

About materials chemistry research at Birmingham

The School of Chemistry at the University of Birmingham has a unique ecosystem of materials chemistry research focusing on sustainable discovery of new materials for tackling the energy and climate crisis. This includes more than 60 academics working in areas such as more efficient batteries, reduction of CO2 emissions, biodegradable plastics, and new materials for light harvesting and emission. A standout feature of research at Birmingham is the widespread use of mechanochemistry, or mechanical milling to create new materials. This highly efficient and rapid method does not require solvents and therefore produces minimal amounts of waste, making it a truly Green Chemistry approach to synthesis. Solid-state NMR plays a key role in understanding the new materials as it provides a unique insight into their atomic-level structure, which is what ultimately determines their macroscopic properties. The combination of state-of-the-art synthetic and analytical capabilities, and high level of expertise makes Birmingham the ideal place for enabling discovery. Commercial partners are encouraged to use the facilities and know-how, as the school advocates for robust business-academia interactions.

The Kubicki team develops in situ NMR strategies to monitor real-time structural changes in functioning solar cells, such as how these materials change when exposed to ambient air, humidity, and light, which are all conditions that cause degradation. Solid-state NMR gives unique element-specific and quantitative insight into local structure, structural dynamics, and chemical transformations in materials.

The Kubicki research group uses various synthetic strategies in conjunction with solid-state NMR, diffraction, and optical spectroscopies to make and understand the new materials our society needs to become more sustainable and end reliance on fossil fuels. The group works closely with the UK High-Field Solid-State NMR Facility at the University of Warwick, which hosts the state-of-the-art Bruker Avance Neo 850 MHz, 1 GHz, and soon the UK’s first 1.2 GHz solid-state NMR system. A new solid-state Avance Neo 400 MHz NMR is scheduled to be installed at Birmingham in June 2024. The team also extensively uses the Bruker solid-state NMR infrastructure at Warwick Physics, where Dr. Kubicki is a Visiting Professor.

“The interaction between Birmingham and Warwick universities has been remarkably productive, as both have excellent infrastructure and brilliant researchers. We are very lucky in the West Midlands to have this unique solid-state NMR, ultrafast spectroscopy and materials community, with a number of research groups studying various aspects of halide perovskites. One could hardly imagine a better place to develop these materials,” says Dr. Kubicki.

“Optical spectroscopies and X-ray diffraction often fall short in providing the answers we seek,” Dr. Kubicki explains. “Solid-state NMR focuses on specific isotopes and has been a game changer for understanding the behavior of individual components within functioning solar cells. One practical example is when we make new halide perovskite solar cells, we are introducing very dilute additives, on the order of 1% relative to the perovskite. Seeing these dilute species with diffraction techniques is essentially impossible. So being able to focus our attention on a specific element with NMR has been key to addressing these challenges.”

Collaboration is a key element of the Kubicki Group’s research. One such effort involves developing multi-junction solar cells which use several different perovskite compositions within a single device to harvest the solar spectrum more efficiently. This work also benefits from solid-state NMR analysis.⁵

“We’ve been collaborating with Northwestern University, IL, USA, on new tandem solar cells, in which we stack different solar cell absorbers on top of each other to harvest the solar spectrum more efficiently,” Dr. Kubicki said. “Solid-state NMR has been critical to try to understand why these compositions work so well.”

New discoveries for optoelectronic applications

In the near future, Dr. Kubicki and his team will be working on expanding the capabilities of solid-state NMR in their research. For example, they are exploring the use of a technique called dynamic nuclear polarization (DNP) with a specific method called magic angle spinning (MAS) to make their NMR experiments much more sensitive and selective. Dr. Kubicki contributed to developing this strategy during his PhD research at EPFL, Switzerland. Before this, DNP had not been applied to halide perovskites, and this research has led to new discoveries for optoelectronic applications.⁶

“MAS DNP can lead to spectacular enhancements in sensitivity: an experiment which would otherwise take a year using a conventional setup can now be carried out within a few hours. It really is a game changer. Yet, MAS DNP had never been applied to halide perovskites and we wanted to find out if it is possible. We have shown that it is indeed applicable to this exciting class of solids.

Specifically, we looked at cesium lead chloride and compared two DNP methods: one involves using a solution of organic biradicals coating the particles of the solid, whereas in the other one we incorporate paramagnetic metal ions (Mn²⁺) into the perovskite structure,” he says. “We found that the metal-ion DNP method works best for getting detailed information about the material's structure, while the incipient wetness impregnation DNP method is excellent for studying the surface of the material. We figured this out by looking at factors such as relaxation times, particle size, dopant concentration, and how the material's surface interacts with liquids. In the future, we believe that DNP NMR methods will be invaluable for determining the atomic-level structure of mass-limited perovskite samples, such as in thin film devices.”

“We are also very excited about combining machine learning with solid-state NMR to better understand halide perovskites. Our long-standing collaboration with Prof. Julia Wiktor and Prof. Paul Erhart at Chalmers University of Technology, Gothenburg, Sweden has already yielded very promising results,”⁷  says Dr. Kubicki.

¹Kubicki, D.J., Stranks, S.D., Grey, C.P. et al. NMR spectroscopy probes microstructure, dynamics and doping of metal halide perovskites. Nat Rev Chem 5, 624–645 (2021). https://doi.org/10.1038/s41570-021-00309-x

²Tiarnan A. S. Doherty et al.,Stabilized tilted-octahedra halide perovskites inhibit local formation of performance-limiting phases. Science374,1598-1605(2021). DOI:10.1126/science.abl4890

³Elisabeth A. Duijnstee, Benjamin M. Gallant, Philippe Holzhey, Dominik J. Kubicki, Silvia Collavini, Bernd K. Sturdza, Harry C. Sansom, Joel Smith, Matthias J. Gutmann, Santanu Saha, Murali Gedda, Mohamad I. Nugraha, Manuel Kober-Czerny, Chelsea Xia, Adam D. Wright, Yen-Hung Lin, Alexandra J. Ramadan, Andrew Matzen, Esther Y.-H. Hung, Seongrok Seo, Suer Zhou, Jongchul Lim, Thomas D. Anthopoulos, Marina R. Filip, Michael B. Johnston, Robin J. Nicholas, Juan Luis Delgado, Henry J. Snaith, Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide, J. Am. Chem. Soc. 2023, 145, 18, 10275–10284. Publication Date:April 28, 2023. https://doi.org/10.1021/jacs.3c01531

⁴Satyawan Nagane, Stuart Macpherson, Michael A. Hope, Dominik J. Kubicki, Weiwei Li, Sachin Dev Verma, Jordi Ferrer Orri, Yu-Hsien Chiang, Judith L. MacManus-Driscoll, Clare P. Grey, Samuel D. Stranks, Tetrafluoroborate-Induced Reduction in Defect Density in Hybrid Perovskites through Halide Management. First published: 04 July 2021. https://doi.org/10.1002/adma.202102462

⁵Wang, Z., Zeng, L., Zhu, T. et al. Suppressed phase segregation for triple-junction perovskite solar cells. Nature 618, 74–79 (2023). https://doi.org/10.1038/s41586-023-06006-7

⁶Mishra, A., Hope, M. A., Stevanato, G., Kubicki, D. J., & Emsley, L. (2023). Dynamic Nuclear Polarization of Inorganic Halide Perovskites. The Journal of Physical Chemistry C, 127(23), 11094-11102. https://doi.org/10.1021/acs.jpcc.3c01527

⁷Julia Wiktor, Erik Fransson, Dominik Kubicki, Paul Erhart, Quantifying Dynamic Tilting in Halide Perovskites: Chemical Trends and Local Correlations. Chem. Mater. 2023, 35, 17, 6737–6744. Publication Date:August 21, 2023. https://doi.org/10.1021/acs.chemmater.3c00933