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How Is Materials Science Shaping the Path to a Greener Future?

Array of solar panels under a bright blue sky, highlighting sustainable materials science innovations.
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The climate emergency is one of the most pressing issues facing humanity this century. Global temperatures have increased by around 1.1°C over the last 170 years, bringing us dangerously close to the 1.5°C rise scientists have warned is the point of no return. 1 We now need to take drastic action to operate more sustainably as a society, whether that's reducing our energy demands or finding cleaner ways to meet our needs.


In particular, reducing emissions and decarbonizing the energy supply are key parts of the global climate strategy. World leaders at COP28 in 2023 pledged to triple global renewable energy generation by 2030, a commitment supported by the striking advances we’re currently seeing in green technologies.2 Similarly, to limit global warming to the 1.5°C target, we must reduce greenhouse emissions by 43% by 2030.1 Both of these goals, while ambitious, are still achievable and materials science is already playing a huge role in creating a more sustainable future.


Materials are fundamental to how we interact with the world – through materials science, we can tailor existing substances or engineer completely novel materials to generate new and useful properties. In this article, we look at some of the materials science research on the frontline of this green transition.

Perovskite solar cells for greener solar power

Solar power accounted for 8% of all energy generated in the UK during spring 2024 and the British government is aiming to quintuple this capacity by 2035.3 Current solar technology is dominated by silicon solar panels, also known as photovoltaic cells, which convert the sun’s energy into electricity via the photovoltaic effect.


“The cells contain a semiconductor material that can absorb photons coming from the sun,” explained Samuel Stranks, professor of energy materials and optoelectronics at the University of Cambridge. “When the photons are absorbed, they energize electrons in the material and those electrons are then collected at electrodes and essentially drive current around the circuit.”


Semiconductors, such as silicon, possess properties intermediate between conductors and insulators, enabling exquisite control of their electronic properties depending on the conditions. But fabricating these materials to the correct specification is no trivial matter.


“Silicon is typically processed at very high temperatures – 1000°C plus – to remove any defects in the material that would otherwise lead to power losses, i.e., where electrons might get trapped and lose their energy to heat,” said Stranks. In addition, the overall cost of establishing solar infrastructure, including installation, parts and maintenance, means that developing more efficient photovoltaic materials is vital to driving down the cost of solar power to a more broadly accessible level.


Strank’s research focuses on developing one such group of these materials. Halide perovskites are a class of ionic compounds containing organic, metal and halide ions arranged in a specific ABX3 crystal structure, and they have already shown promise as a low-cost alternative to silicon solar cells. Unlike silicon, perovskite structures are easy to prepare, requiring much lower temperatures and tolerating relatively crude processing. And while silicon cells must be cut from shaped ingots, perovskites are easily fabricated into micron-thick sheets, and can even be printed directly onto metal or plastic surfaces.4


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The efficiency of perovskite solar cell systems has skyrocketed in recent years, rising from about 3% for early designs in 2009 to over 26% today – comparable with the best silicon systems. 5, 6, 7 Crucially, by manipulating the fundamental chemical structure of the perovskite sample, it’s possible to tune the parts of sunlight that the material can absorb, theoretically boosting this efficiency even further, said Stranks.


“The compositions of particular ions that we choose from the periodic table are very important. The size of the ions, the specific charge of the ions, these dictate what the chemical structure looks like,” he explained. “The chemical structure is directly linked to what's called its “band structure”, which determines its electronic properties, including which wavelengths of light it absorbs and how well it can transport charges.”


A multinational team of collaborators, including Stranks, recently reported a micron-thick formamidinium-based perovskite cell with a record efficiency of 26.1%.6 Their thin-film device opens the door to alternative applications of solar cells, beyond static energy generation on buildings or solar farms. “For example, having a very high-efficiency solar module on electric vehicle rooftops that can boost the range could really change the dynamics of electric vehicles and help decouple from this situation where we rely on plug-in infrastructure,” said Stranks. “There are also applications in space because of this lightweight, high-performance, high-power aspect.”


However, the greatest impact of perovskite cells will most likely be in combination with silicon or other perovskites in multi-junction devices, where different layers of semiconductor are stacked together. “There’s a thermodynamic limit on how much of the solar sunlight we can capture and convert to electricity,” Stranks explained. “For one layer the absolute thermodynamic limit is 33%.”8


This limit is an innate feature of the photovoltaic effect responsible for generating electricity within solar cells. To energize an electron across the semiconductor’s bandgap, from the lower insulating band to the upper conducting band, the incoming photon must have a certain minimum amount of energy, equivalent to the size of the bandgap. As result, lower energy wavelengths such as near-infrared don't have sufficient energy to excite electrons across this space and therefore can’t produce harvestable electricity. At the other end of the spectrum, high-energy wavelengths such as ultraviolet photons supply far more energy than is needed for this transition, and the excess is simply discharged as heat. Combined, this means that a single solar cell can only harvest a slice of all the available light energy.


“But when you use two layers, that limit starts to go up to more like 45% as you can use each of those layers to harvest a slightly different region of the spectrum,” Stranks said.9 “The best perovskite tandem cells are currently at just over 34% which is a really exciting result.”7


Several challenges remain in translating this research from lab to commercial scale, from depositing material uniformly over large areas, to understanding long-term degradation pathways. But according to Stranks, current results are promising. “If we can get perovskites to a higher efficiency than silicon and be similarly stable, in particular when they're combined in multiple layers, that would be a game changer for solar,” he said.

Biochar concrete for reducing the impacts of construction

“If you look at the carbon emissions from different sectors, almost 40% come from buildings,” said Mehreen Gul, an assistant professor in architectural engineering at Heriot-Watt University.10 The day-to-day running of a building is an energy-intensive process. Heating, lighting, ventilation, not to mention other mundane activities such as cooking, cleaning or working at a computer all contribute. With the average person spending more than 80% of their time inside, it all adds up to a substantial carbon footprint. 11


Strides have been taken in recent years to design net-zero buildings – structures capable of fully meeting their own energy demands by generating power onsite from renewable resources. But even these greener edifices have a hidden carbon footprint. “When we talk about net-zero buildings, we mostly talk about how much energy the building uses once it's constructed – the operational energy. But often we don't really think about the energy that goes into the whole process, the embodied energy of construction,” Gul explained. To effectively decarbonize the building sector, Gul believes we need to take a broader approach, considering the whole of the building lifecycle from preconstruction material selection through to end-of-life demolition.



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Construction materials themselves are heavily implicated in emissions throughout the building lifecycle. Cementitious composites such as concrete in particular are a big focus of current materials research. “Cement and concrete are the two key ingredients of any building project and both require a high-temperature, energy-intensive process to manufacture,” said Gul. It’s estimated that up to 8% of annual global CO2 emissions are from the manufacture of cement.12


Gul’s latest research project focuses specifically on replacing a proportion of this problematic cement in concrete with biochar, a type of charcoal obtained by heating waste organic material without (or with limited) oxygen. The feasibility of such substitutions is already well-known, with ash, tyres, ceramic powder and even coffee grounds having been successfully incorporated into concrete mixtures. 12, 13, 14, 15, 16 But Gul wants to take this one step further, probing how this material switch directly impacts the carbon footprint of buildings.


“We already have some evidence in terms of the properties when biochar is used in material concrete. For example, replacing 1% within a cementitious composite, the compressive strength can increase by 10%.17 It can also act as an insulation material, minimize moisture and absorb some pollutants,” she said. “One of the key angles of the project is looking at when the biochar is used in a specific building type, how much impact it has in terms of minimizing the energy demand of that building.”


Crucially, this isn't just about reducing the operational energy demands of buildings. Biochar is a carbon-negative material, meaning that incorporating it into concrete offsets carbon during the construction phase. “The process of creating biochar from biomass is one which locks carbon,” Gul explained. “If you didn't do anything with, for example, fallen leaves, over time they would degrade and start releasing the carbon that they absorbed at the time of growing. Instead, we remove that carbon type from the environment.”


Over the remainder of the project, Gul’s team will investigate how different feedstocks and preparations of biochar influence the properties and suitability of the resulting composite such as concrete for different building applications, exploring how this impacts the operational energy demands across a range of building types. But, a key part of making biochar concrete a realistic commercial alternative to conventional cement will be involving stakeholders in the development process said Gul. “We will need a lot of input from industry because academically, we could come up with a fantastic solution but it would just be academic. Without having the input of the people who produce or use the material on a day-to-day basis, we won't be able to achieve success.”


At present, the work is at an early stage but Gul is optimistic about the potential of biochar and hopes that the project will raise awareness of the environmental footprint encapsulated within buildings. “I think the biggest challenge is that the focus needs to be on both reducing operational and embodied costs,” she concluded. “It’s the whole lifecycle energy that we need to minimize.”

Materials science for a greener future

Regardless of the application, it's clear that understanding material properties and how to engineer them will be crucial for the green transition. As Stranks and Gul have shown through very different examples, materials science is already coming up with solutions to tackle the climate crisis and over the next 10 years we will hopefully see these revolutionary materials reaching the wider public on a commercial scale.


References

1. Intergovernmental Panel on Climate Change (IPCC). Technical Summary. In: Climate Change 2021 – The Physical Science Basis. Cambridge University Press; 2023:35-144. doi: 10.1017/9781009157896.002

2. Heads of State and Governments as the Participants in COP28. COP28 Global Renewables and Energy Efficiency Pledge. https://www.cop28.com/en/global-renewables-and-energy-efficiency-pledge

3. Department for Energy Security and Net Zero. Energy Trends September 2024.; 2024. Accessed November 22, 2024. https://assets.publishing.service.gov.uk/media/66f423473b919067bb48270e/Energy_Trends_September_2024.pdf

4. Weerasinghe HC, Macadam N, Kim JE, et al. The first demonstration of entirely roll-to-roll fabricated perovskite solar cell modules under ambient room conditions. Nat Commun. 2024;15(1). doi: 10.1038/s41467-024-46016-1

5. Kojima A, Teshima K, Shirai Y, Miyasaka T. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J Am Chem Soc. 2009;131(17):6050-6051. doi: 10.1021/ja809598r

6. Li S, Xiao Y, Su R, et al. Coherent growth of high-Miller-index facets enhances perovskite solar cells. Nature. 2024. doi: 10.1038/s41586-024-08159-5

7. NREL. Best Research-Cell Efficiency Chart. https://www.nrel.gov/pv/cell-efficiency.html

8. Rühle S. Tabulated values of the Shockley-Queisser limit for single junction solar cells. Solar Energy. 2016;130:139-147. doi:10.1016/j.solener.2016.02.015

9. Peters IM, Rodríguez Gallegos CD, Lüer L, Hauch JA, Brabec CJ. Practical limits of multijunction solar cells. Progress in Photovoltaics: Research and Applications. 2023;31(10):1006-1015. doi: 10.1002/pip.3705

10. UK Government. Heat and Building Strategy Report. Published online 2021. https://dataenergy.co.uk/heat_and_buildings_strategy_published/

11. Bunn S, Duffield G. Indoor Air Quality Report. https://post.parliament.uk/research-briefings/post-pb-0054/

12. Afrin H, Huda N, Abbasi R. An overview of eco-friendly alternatives as the replacement of cement in concrete. IOP Conf Ser Mater Sci Eng. 2021;1200(1):012003. doi: 10.1088/1757-899x/1200/1/012003

13. Lazik PR, Garrecht H. Wood ashes from electrostatic filter as a replacement for the fly ashes in concrete. In: Fib Symposium. fib. The International Federation for Structural Concrete; 2020:118-124. doi: 10.36756/jcm.v2.2.6

14. Siddika A, Mamun MA Al, Alyousef R, Amran YHM, Aslani F, Alabduljabbar H. Properties and utilizations of waste tire rubber in concrete: A review. Constr Build Mater. 2019;224:711-731. doi: 10.1016/j.conbuildmat.2019.07.108

15. El-Dieb AS, Kanaan DM. Ceramic waste powder an alternative cement replacement – Characterization and evaluation. Sustain Mater Technols. 2018;17. doi:10.1016/j.susmat.2018.e00063

16. Roychand R, Kilmartin-Lynch S, Saberian M, Li J, Zhang G, Li CQ. Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength. J Clean Prod. 2023;419. doi: 10.1016/j.jclepro.2023.138205

17. Akinyemi BA, Adesina A. Recent advancements in the use of biochar for cementitious applications: A review. J Build Eng. 2020;32. doi: 10.1016/j.jobe.2020.101705