In the global race to develop new materials for clean and cost-effective energy solutions, a crystalline structure has shown promise as a semiconductor that, say industry experts, is set to become the primary raw material for a new generation of photovoltaic solar panels. Perovskite modules developed in laboratories using chemical compounds such as lead bromide, lead iodide, and cesium bromide have proven to be highly efficient in converting photon energy into electricity. The first research exploring perovskite’s unique properties was published in 2009, when a groundbreaking paper in the Journal of the American Chemical Society demonstrated its use for the first time as a component in photoelectrochemical solar cells. Since then, research groups around the world have joined in studying the material.
Rapid progress in research and development of perovskite cells has set researchers and startups on a race to make them commercially viable (see Pesquisa FAPESP issue nº 260). In under 15 years, the conversion efficiency of these solar cells—which have the advantage that they can be made flexible, lightweight, and transparent—has leaped from 3.8% to 26.1%. These levels were achieved with modules with a relatively small surface area. In comparison, the efficiency of commercial silicon-based solar panels, which currently dominate the market, ranges from 15% to 20%.
A more recent technology known as tandem solar cells—in which a perovskite solar cell is overlaid on a silicon cell—has recently demonstrated an efficiency of 33.7% in the lab. The new world record was set in June 2023 at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia. The US government’s National Renewable Energy Laboratory (NREL) maintains a chart of the highest confirmed conversion efficiencies achieved at various research centers worldwide over the past few years.
Companies and startups in China, the US, and Europe are set to start large-scale production of perovskite solar modules in the upcoming months. One example is British-based Oxford Photovoltaics, a spin-off from the University of Oxford that operates a state-of-the-art manufacturing line for perovskite-on-silicon tandem solar cells in Germany. In the US, Caelux is building a facility to upscale its production of perovskite photovoltaic glass, with first deliveries for building solar modules anticipated within the year. In 2023, Chinese-based GCL-SI unveiled a 320-watt perovskite solar module boasting an efficiency of 16%, noting that it is currently being produced at pilot scale.
In Brazil, the organization closest to a commercially viable perovskite cell model is Oninn, a nonprofit, private organization based in Belo Horizonte, formerly named CSEM Brazil until 2022 (see Pesquisa FAPESP issue nº 247). The initiative is a collaboration between researchers from São Paulo State University (UNESP) and the Center for Innovation in New Energies (CINE), an Engineering Research Center (CPE) established in 2018 by FAPESP and Shell Brazil. However, commercial-scale production of technically and economically viable perovskite cells is still a long way off.
Leveraging its experience from developing solar panels using organic photovoltaic cell technology, Oninn is currently working to scale up its perovskite-based cells from laboratory scale—no larger than a few square millimeters or centimeters (cm2)—to larger modules measuring hundreds of cm2 as required for commercial applications.
“We’ve successfully produced our first prototype perovskite panel with an area of 800 cm2. But our standard panel, which is still under development, is slightly smaller at 500 cm2,” explains Diego Bagnis, an Italian physicist and scientific director at Oninn, who has been involved in the research effort in Brazil over the past nine years. “We’re still in the prototyping phase, testing our first real-world applications to validate the technology.” Bagnis hopes to have a pilot manufacturing line set up by 2026 and to go to market in 2028, initially targeting small-scale applications.
Oninn is not currently developing tandem cells. “We are focusing on what is known as a single-junction solar cell, or a cell with only one layer of perovskite,” says Bagnis. “Making tandem cells—with perovskite overlaid on silicon—makes sense in Europe as silicon technology is well-established there and they have local production facilities to produce these cells. But this is not the case in Brazil.” Local producers in the country import the silicon-based materials used to make solar panels, and only assemble the modules locally.
Despite recent advancements and promises of soon-to-be-launched commercial models, Brazilian researchers interviewed for this article say they are still a way from understanding the properties of this emerging material, especially as they relate to cell stability—or the ability to retain mechanical integrity over an extended period—and how to replicate the energy efficiency achieved in the lab in larger-scale modules.
“There are still scientific and technological hurdles that will require investment, time, and expert personnel to overcome,” says physicist Carlos Frederico de Oliveira Graeff from the UNESP School of Sciences, Bauru campus.
Graeff, who is developing perovskite solar cells and is a member of Oninn, explains: “From a physics and engineering standpoint, silicon is a relatively simple material with a known crystal arrangement, whereas perovskite is physically and chemically complex. It is generally composed of both organic and inorganic components, consists of multiple elements, and exhibits high ionic mobility.” One of Graeff’s most recent projects, with funding from FAPESP, is precisely investigating the stability of these solar cells.
Gustavo Dalpian, a physicist at the University of São Paulo (USP) Institute of Physics, notes that many fundamental properties of the material’s crystalline structure are still not well understood. “It’s quite different from what we see in other materials. In crystalline silicon, for example, atoms tend to stay in well-defined positions, but in perovskites, they move a lot. This is believed to be one of the reasons they are so unstable.”
Perovskite’s instability, causing it to degrade much faster than silicon, is one of the major barriers to commercial production. While silicon modules can last up to 30 years with minimal loss of efficiency, cells made of the new material can barely last a little over a year. Early cell models degraded within hours or days. Moisture, heat, oxygen, and even sunlight can degrade them.
“Once we understand the structural properties of these materials and their flaws, we can develop or think of ways to prevent them from degrading as fast as they do today,” says Dalpian. The research group he leads specializes in computational modeling of materials using big data and machine learning.
He recently visited Colombia as part of a FAPESP Sprint project, where he spoke with Pesquisa FAPESP. “We are discussing new projects involving perovskites, and researchers from two universities in Medellín are expected to join the initiative,” says Dalpian, who is also collaborating with an experimental group at the Federal University of ABC (UFABC), where he lectured until receiving tenure at USP in 2023.
Synchrotron light and perovskite
In an in-depth investigation of perovskite properties, a team at CINE were the first to observe it using one of the synchrotron light sources at Sirius, operated by the Brazilian Synchrotron Light Laboratory (LNLS) at the Brazilian Center for Research in Energy and Materials (CNPEM). CINE brings together researchers from the University of Campinas (UNICAMP), USP, and the Institute for Energy and Nuclear Research (IPEN).
“Studies into the use of perovskite in photovoltaic applications have been among the fastest-growing energy research niches globally, and our experiments with synchrotron light have allowed us to gain a foothold in an extremely competitive research environment,” says chemist Ana Flávia Nogueira, CINE’s director and a professor at the UNICAMP Institute of Chemistry. She has been researching emerging photovoltaic materials since 1996, and in 2015 began investigating perovskite materials.
With the scientific instruments available at CNPEM, the researchers were able to analyze the material on a nanoscale in real time. “We brought the equipment used to produce the perovskite film—a rotating disk called a spin-coater, which resembles a CD burner—to the X-ray beamline,” says Nogueira. This was the first experiment of this kind . But why is this kind of experiment—known as in situ X-ray diffraction—particularly useful? “As the perovskite film was forming, X-rays struck the sample, providing useful information about the structure and how the film crystallized at each stage,” explains Nogueira.
This and other tests to analyze the degradation of the material, also employing in situ techniques at Sirius, gave wide visibility to the researchers at CINE, leading to an invitation to write a review on the subject for the journal Chemical Reviews. The 77-page article was published in early 2023. “The invitation to author a review article for a high-impact journal crowns the work we have been doing in recent years,” says Nogueira. In addition to investigating the use of perovskite to make solar cells, the group is also exploring applications for the material in light-emitting devices, such as LEDs and lasers.
Understanding how it works
At Sirius, the current focus of experiments is understanding how perovskite solar cells work, and not just the material itself. These experiments are termed “operando” experiments. One of the challenges in this type of analysis is that synchrotron radiation can induce undesired changes in the material.
“We are investigating the effects of the radiation dose required to study these devices and how to mitigate them. We’ve already developed devices to simulate the operating conditions of photovoltaic solar cells, and have produced some initial results,” says physicist Helio Cesar Nogueira Tolentino, head of the Division of Heterogeneous and Hierarchical Matter at LNLS. “We’re working on fine-tuning the optimal working conditions for obtaining information using synchrotron light without degrading the photovoltaic material, or if degradation occurs, to ensure it is in a controlled manner.”
Tolentino explains that perovskite’s crystalline structure typically resembles a cube, but can vary depending on the preparation method or synthesis route. In their first operando experiment, the researchers observed the impact of sunlight on the material’s atomic structure. “While we have not yet come to a definitive interpretation, there is evidence suggesting that varying light levels alter the material’s structure.”
The Brazilian researchers are investigating a number of potential solutions to prevent the material from acquiring undesirable properties for the intended application, including additives, new molecules, modifications to the film production process, and even a two-dimensional (2D) perovskite film overlayed on a three-dimensional (3D) layer. However, the material’s instability is just one of many technological hurdles. Sustaining the energy efficiency achieved with lab-scale cells on a larger scale is also a complex puzzle.
“The scaled-up cells are often not homogeneous,” explains Nogueira from UNICAMP. “The crystallization process that occurs as perovskite forms differs from that of other materials used in photovoltaics.”
According to Graeff, researchers are currently working to develop formulations and processes to make the technology economically viable. “We need robust production processes that can be used on a large scale. In the meantime, we’re learning a lot about the fundamental physics and chemistry. These materials are complex and their use in electronic devices is fairly incipient,” says Graeff. “The electronics used for current solar panels is designed for silicon, a very simple and stable material. Now we are dealing with a material composed of different chemical elements and with a complex structure.”
Oxford PV
A tandem solar cell production line at the Oxford Photovoltaics facility in Germany
Oxford PVResearch in this field offers good examples of successful collaboration between theoretical and experimental scientists. Using computer modeling, theorists can design structures that have never been created in the lab or save time and costs in selecting elements to be tested in experiments.
“We analyze different materials and try to infer or learn about their properties,” says Dalpian, who has coauthored at least five papers with the experimental group at UFABC. “Our collaboration has been highly productive. Typically, experimental researchers make requests and we oblige, but in our case they also listen to our input. For instance, we once suggested that introducing iron into perovskite could impart useful magnetic properties. They tried it, and the results led to an interesting article,” recounts Dalpian.
At CINE, theoretical and experimental researchers are collaborating on multiple research fronts. One project is working to develop alternatives to lead (a toxic substance) in the composition of perovskite. “There are obvious benefits from reducing or completely eliminating lead content in these structures,” says Juarez L. F. da Silva, a physicist at the USP Institute of Chemistry in São Carlos (IQSC) and coordinator of the Computational Materials Science program at CINE.
“Computational modeling can be used to simulate a large number of materials to replace a given element in low-dimensional perovskites—such as tin, germanium, or combinations of two chemical species,” explains Da Silva. The material must fulfill as closely as possible a particular set of parameters. “We use experimental information to identify materials that can meet these specifications.”
Another research program, led by experimental researchers at CINE, is exploring how molecules interact with perovskite surfaces. The team is using computer modeling to discover mechanisms that might contribute to cell degradation, says Da Silva. “In a solar cell, the metal wire used to carry electrical current interacts with the perovskite, causing chemical species to be carried from one side to the other. In some circumstances, they can destabilize the cell structure.”
According to Dalpian, perovskite solar cells can be used in a wide range of applications but this will require a breakthrough in cell stability. “By today’s standards, a solar cell is expected to last 20 to 25 years. But it doesn’t necessarily have to be that way. If cells are considerably cheaper, they can be replaced when they become less efficient, as we do today with light bulbs,” says Dalpian. “But there would need to be an ecosystem in place to recycle end-of-life panels, minimizing their environmental impact.” The goal of current perovskite cell research is not necessarily to completely replace silicon modules but to incorporate an additional material with useful properties and characteristics into the solar energy value chain.
Projects
1. Research Division 1 – Dense energy carriers (nº 17/11986-5); Grant Mechanism Energy Research Centers (CPEs); Principal Investigator Ana Flávia Nogueira (UNICAMP); Investment R$10,273,024.78.
2. Advanced characterization of Pb-free perovskite-based nanomaterials by X-ray (nº 21/06434-9); Grant Mechanism Regular Research Grant; Principal Investigator Hélio Cesar Nogueira Tolentino (CNPEM); Investment R$295,909.01.
3. Computational design of stable halide perovskites: Effects of defects, alloys, and pressure (nº 21/14422-0); Grant Mechanism Regular Research Grant; Principal Investigator Gustavo Martini Dalpian (USP); Investment R$265,031.36.
4. Discovery and design of new compounds: Halide perovskites and quantum materials (nº 22/14221-8); Grant Mechanism Regular Research Grant; Principal Investigator Gustavo Martini Dalpian (USP); Investment R$46,975.80.
5. Material interfaces: Electronic, magnetic, structural, and transport properties (nº 17/02317-2); Grant Mechanism Thematic Project; Principal Investigator Adalberto Fazzio (CNPEM); Investment R$8,462,036.42
6. Optimization of the stability of perovskite solar cells (nº 20/12356-8); Grant Mechanism Thematic Project; Principal Investigator Carlos Frederico de Oliveira Graeff (UNESP); Investment R$1,919,506.81.
7. Investigations of electronic transfer processes in photoactive devices (nº 19/23277-4); Grant Mechanism Regular Research Grant; Principal Investigator André Sarto Polo; Investment R$182,003.06.
8. Cine: computational development of materials for energy applications using atomistic, mesoscale, multiphysics and artificial intelligence simulations (nº 17/11631-2); Grant Mechanism Engineering Research Centers (CPEs); Principal Investigator Juarez Lopes Ferreira Da Silva (USP); Investment R$4,758,140.41.
Scientific articles
KOJIMA, A. et al. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. Journal of the American Chemical Society. Vol. 131 (17), pp. 6050–1. 2009.
SZOSTAK, R. et al. In situ and operando characterizations of metal halide perovskite and solar cells: Insights from lab-sized devices to upscaling processes. Chemical Reviews. Vol. 123, pp. 3160–236. 2023.
SCALON, L. et al. Improving the stability and efficiency of perovskite solar cells by a bidentate anilinium salt. JACS Au. May 4, 2022.
LEMOS, H. et al. Electron transport bilayer with cascade energy alignment based on Nb2O5–Ti3C2 MXene/TiO2 for efficient perovskite solar cells. Journal of Materials Chemistry C. Vol. 11, pp. 3571–80. Jan. 2023.
BONADIO, A. et al. Entropy-driven stabilization of the cubic phase of MaPbI3 at room temperature. Journal of Materials Chemistry A. Vol. 9, pp. 1089–99. Jan. 2023.
SABINO, F. et al. Intrinsic doping limitations in inorganic lead halide perovskites. Materials Horizons. Vol. 9, pp. 791–803. 2022.
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