We spoke to new Fellow in Physics Dr Nakita Noel about her research into how new materials could transform solar energy.
Your work sits at the crossroads of Physics, Chemistry, and Materials Science. How do you describe what you do to someone outside your field?
One of the most fascinating and, in my opinion, most important technological developments is to control the interaction between light and matter. One of the most well-known applications in this area are photovoltaic solar cells where light is absorbed by a semiconductor and converted into electrical power. In LEDs or lasers, this process happens in reverse, where we apply electrical power to a semiconductor and thus produce light. What I am personally interested in is the development of new materials that have outstanding light-matter interactions. Importantly, my interests span from conceiving of the elemental composition, to the synthesis and characterisation, to the eventual application in a device.
To what extent are you driven by pure scientific interest in your research and to what extent are you motivated by wanting to affect change, for example to address climate challenges?
Being interested in Physics stems from my childhood; I was the youngest of four and looked up to my big brother in particular who was studying Physics. He would teach me what he was learning about, and I clearly remember the book he used and how it sparked my curiosity about how the world worked. When you start studying Physics initially, you spend a lot of time learning things that just have to be learnt but it’s good to pause a moment and ask what something really means. Maybe you know the fine detail but it’s good to look up and think oh, that’s what it does, that’s why this is the way it is. It’s this real-life aspect that makes it exciting. I like solving puzzles and I think science is the best way to do that. So, the thing that really motivates me is yes, doing cool science but doing cool science with a purpose. One day, maybe ten years from now, I might look up and see halide perovskites on someone’s roof and say hey, I worked on that.
I like solving puzzles and I think science is the best way to do that.
You’ve talked about being a translator between Chemistry and Physics; can you explain what you mean by this?
The thing that’s interesting about the specific area I work in is that you can’t really get a full understanding of these systems by just doing the Physics or just doing the Chemistry. You must understand what’s going on with every component of a semiconductor system and how these different areas impact on each other. For me the breakthroughs happen when you can look at things from every angle and stitch together what’s going on. Very often Chemists and Physicists are saying the same thing but using different language to say it. If you can see this, make the connections and fill in the gaps, then things will click into place.
What first drew you to study semiconductor materials and what makes them so fascinating to you?
I’m very intrigued by light-matter interactions but specifically, the development of new solar cell materials drew me to the field. Solar cells are such an obvious solution to our increasing need for more energy without the catastrophic downsides of increased fossil fuel consumption. What is required to make solar power more ubiquitous and to truly rival conventional energy sources is to make its deployment even cheaper and its initial carbon footprint even smaller.
Can you explain how you are working with new materials to improve their photovoltaic application for solar energy and other technologies?
Halide perovskites are currently the most promising new material class that has the potential to significantly boost solar technologies. There is a variety of properties that sets these semiconductors apart from their conventional cousins, but there are a few that are truly noteworthy:
- Because they are such good absorbers, even extremely thin layers absorb practically all available light. To put some numbers it, the average human hair has a diameter of about 75 ÎĽm, a perovskite absorber layer is about 150 times thinner.
- By modifying the elemental composition of the halide perovskite, we can change its bandgap which determines the fraction of the solar spectrum it can absorb. This allows us to stack several layers of different compositions on top of each other to absorb different fractions of the solar spectrum separately, and thus we can substantially increase the overall conversion efficiency of such so-called “tandem” stack compared to solar cell containing a single absorber layer.
- A third amazing property is the fact that these materials can be deposited with a variety of deposition methods such as thermal evaporation or inkjet printing without requiring highly specialised high-temperature ovens for example.
All these properties have direct implications on the technology as part of the renewable energy source portfolio, for example the use of tandem solar cells. At the same time, modulating and controlling these properties requires a deep understanding of the fundamental relationship of the absorber Chemistry and Physics. It is very exciting to me that even when I work on some of the most fundamental aspects of this technology the ramifications of my findings often have a direct impact on the technology on a much more applied level.
It is very exciting to me that even when I work on some of the most fundamental aspects of this technology the ramifications of my findings often have a direct impact on the technology on a much more applied level.
You’ve developed new ways to control crystallisation. Can you explain how this might change the stability or efficiency of future solar materials?
Crystallisation is probably the most important process of making perovskite solar cells. The reason is that this process not only controls the quality of the absorber but will also determine its longevity. The underlying mechanism is that during this process the order of the crystal is set. The more disorder or defects the crystal contains, the less efficient and resilient the absorber will be. Especially, high absorber durability is critical for solar cells since once they are part of a solar panel, we want them to continuously and efficiently convert sunlight into electricity for decades.
You study how materials assemble themselves. What’s the biggest challenge in understanding such complex processes at the atomic level?
Ha. I’m not sure there is one biggest challenge. Everything is challenging, but that’s what keeps it fun! In general, we have to use inference from certain observation to draw larger conclusions regarding processes and mechanisms. However, often a lot of uncertainty remains as to what actual happens on the atomic or molecular level. That’s one of the motivations of my research to use cryo-electron microscopy and nanodiffraction to take actual snapshots of processes taking place at the atomic level. Here one of the biggest challenges is that the mere process of looking at the material may impact its behaviour, so we need to be very careful and diligent to ensure that our observations are not the result of us taking these snapshots.
What does this mean in the context of making new kinds of solar panels?
One of the ways I describe it to people is by getting them to think of the best cake they have ever eaten and then I say I will give them the ingredients for it but no recipe and ask if they think they can recreate that exact cake. The answer is probably not. But if I give you the recipe then you probably could. Depending on what kind of cake you want to make, the different methodologies matter: you can’t just throw all the ingredients together without mixing them properly. This is similar to making multi-component materials because you are bringing a lot of things together and hoping for the best but things at the nano-scale can actually be very different to how they look at the macroscale. You may think everything is perfect, but at the atomic scale things are not perfect at all. How can I control that? To control it, you need to understand it so we spend a lot of time doing electron microscopy and trying to figure out how if we change the way we put the elements together it can change the integrity of the material we create at the nanoscale. If we can control the integrity of the material at the nanoscale, does it affect long-term device stability? The answer to that question is yes, and we have a paper forthcoming to explain more. I find it very cool to try to understand the entirety of a system from literally how the atoms come together, to a product you can put on your roof to power your home.
I find it very cool to try to understand the entirety of a system from literally how the atoms come together, to a product you can put on your roof to power your home.
You teach a wide range of topics, from optics to statistical Physics. What do you most enjoy about teaching Queen’s students?
Obviously, the students. Getting my footing as a new Tutorial Fellow still feels quite daunting sometimes because you’re teaching a lot of things! What is a thoroughly redeeming aspect, however, is when I can see how the penny drops and one of my students goes from being completely confused to having this amazing spark of understanding. That is really gratifying. They often push my understanding as well because they never stop asking why! It’s really fun to be honest; we have some great Physics students at Queen’s and I really enjoy teaching them.
How does your research influence the way you teach, and vice versa?
In my research I try to connect the most fundamental science to applications. This holistic view is something that definitely shapes how I think about teaching. Meaning, I want my students to consider the larger picture, especially when they get bogged down in the details of a problem. I think the ability to zoom out and take the wider perspective is a critical skill for scientists to have which is what I’m trying to impart to all my students…even at the graduate level!
You supervise students at every level, from MPhys projects to DPhil researchers. What do you look for in a good research question or student project?
For MPhys and student projects, the research question needs to be well-circumscribed and self-contained, while still remaining interesting. In contrast, DPhil projects should start with an open and original question. To a large extent, I expect my DPhil student to develop their very own approach to asking the important questions, as I see asking the right questions as one of the most important developments for any budding scientist. A good research question should seek to fill a gap in our understanding, and (hopefully) is something we can build on so that we gain a deeper understanding of the world in which we live.
A good research question should seek to fill a gap in our understanding, and (hopefully) is something we can build on so that we gain a deeper understanding of the world in which we live.
What do you think makes Physics at Oxford particularly exciting?
One aspect of Physics at Oxford, in particular Condensed Matter Physics, that I personally find very exciting is that we span the entire spectrum from very fundamental research to very applied technology development. We’re also a big department and cover so many areas of Physics that there’s always something new to learn!
Your research could play a role in the future of sustainable energy. How do you see Physics contributing to solving global challenges?
New technological developments, especially in the area of energy generation and storage, will be key in tackling global challenges. Here, I see Physics, and especially the kind of Condensed Matter Physics that also incorporates important aspects of Chemistry and Materials Science, as one of the most critical fields of science.
Science often advances through collaboration. How do you bring together physicists, chemists, and engineers in your work?
Since my group’s research focus is truly at the overlap of Physics, Chemistry, and Materials Science (and a little black magic), that is reflected in my team members as well who also have diverse scientific backgrounds. It allows us to look at a problem from various aspects and develop a holistic understanding of a given problem. I appreciate the fact that we all have such varied expertise that somehow overlaps perfectly. Personalities are important too! I’m really fortunate that people in my team get along so well…having fun together makes the work so much more satisfying because you succeed as a team. In my collaborations, I also work frequently with groups in the Materials or Chemistry departments and there, the same principles apply.
The field of Materials Science is evolving fast – what’s on the horizon that excites you most?
Specifically in my field, there’s a variety of emerging materials that have been predicted to have very interesting light-matter interactions, but so far no one has been able to make and/or characterise them. More broadly, I think leveraging large-data sets and artificial intelligence to predict materials and properties has a lot of potential to be very exciting, particularly as it means people like me have more materials to probe.
In your opinion is using AI with large data sets its main strength?
I am not an AI sceptic, but I am cautious. I am a firm believer that if you’re going to do something, you should do it right so, because it’s not my area of expertise, I prefer to hold off until I know what I’m doing! The kinds of things we do use it for already are pattern recognition and helping us sort data. We can, of course, do this without AI, it just takes significantly longer. This is very different from a student taking their problem sheet to ChatGPT and asking for the answers. Used correctly these tools can aid understanding of concepts but there’s a real problem if you outsource all your work to them because then you don’t actually understand anything.
What do you advise your students to do in order to gain genuine understanding?
I always try to teach my students early on not just how to ask the right question but how to sanity check yourself because people can easily get stuck in a problem and no longer critically evaluate the way they are thinking about it. That’s one of the reasons why collaborating with people is so important. When others challenge your ideas, it helps you reset your bearings. Scientists need ongoing ways to verify their assumptions so that their hypothesis remains the best one supported by the data. It’s not about having an absolute right answer (though you may have one) it’s about formulating the best and most logical explanation you can given everything you have in front of you.
When others challenge your ideas, it helps you reset your bearings.
Is that why you encourage the undergraduates to work as a cohort?
Absolutely. It’s also because nobody is brilliant at everything, I’m certainly not! It’s important to recognise the things that are not your strength and you have two choices at that point: you can find someone else who is good at them and work together, or you can say I want to be good at this too and find someone who can teach you. Either way, you are collaborating. You will get a more complete answer when you look at a question from different points of view and learn from others, and the best part of science is continuously learning new things.
What do you enjoy about being at Queen’s?
I think one of the really great things about being at Queen’s is being frequently exposed to so many different people who are in different disciplines. Everyone is very friendly, and you always end up having the most fantastic conversations. I always really look forward to having those seemingly unrelated conversations that really make you start thinking about your own work in a new light, but especially the ones that are so far out of your wheelhouse. There’s always something new to learn and it’s awesome having so many willing teachers!
Can you recommend a book?
The Knowledge Machine by Michael Strevens is a very interesting account of how the scientific method evolved and what its foundations are. I think especially for students who are considering a career in a scientific field this book is immensely valuable because it highlights the very foundations of modern science.
Header photo: David Olds
