Introducing Graham Carey, quantum dot researcher

Graham Carey wants to make quantum dot solar energy systems more efficient and the Natural Sciences and Engineering Council of Canada's doctoral Andre Hamer Postgraduate Prize may help him do just that.

Quantum dots—microscopic pieces of semiconductor—capture different kinds of light depending on the size of the dot, and can be layered onto a surface from a liquid, like paint. Carey’s research looks at ways of making the individual layers more stable. He is also strengthening the connections between layers to minimize current and voltage loss to create a more efficient system.

Carey works with the University of Toronto's cross-disciplinary Sargent Group which researches applications for discovery in nanoscience.

U of T News asked Carey to discuss his work and its implications for future generations.

Tell us about your research:

Solar energy is a growing and increasingly visible field of research, but solar faces a fundamental roadblock – the standard solar panels you see on a roof or at a solar farm are bulky, tough to install and maintain, usually only convert about 15 percent of sunlight into electricity, and critically, are still far too expensive to compete with fossil fuel economically. My research is looking at ways to address all of these problems simultaneously.

We are developing brand new materials for solar cells; instead of using large blocks of silicon, we start with nanometer-scale chunks of material called quantum dots (roughly 30,000x smaller than the thickness of a hair) suspended in liquid and coat very thin layers of these particles on a wide variety of backing material. Because the active light absorber is so thin, we can make these films on flexible, lightweight backbones (think of a painted layer on a thin plastic sheet) and then deploy them virtually anywhere – no more worrying about having a reinforced roof to hold a solar panel, not to mention potential applications in cars or in personal "solar charging stations." The small amount of material used and the greatly reduced weight go a long way to reducing the costs of this solar technology.

Additionally, the physical nature of the nanoparticles themselves allow us to capture light energy in the range untouched by standard solar panels. Roughly a third of the sun's energy is in the invisible, infrared spectrum, and while silicon solar panels cannot absorb this energy at all, we can absorb wherever we want in the solar spectrum just by tweaking the size of our nanoparticles.

What kind of impact could this research have for society?

This research has the potential to completely transform how we think about electricity generation. In the past eight years, this field has gone from being able to convert one percent of sunlight into electricity to current records of over seven percent – blazing-fast progress in such a new field.

At this pace, quantum dot solar cells could be market ready (ideally able to convert 10-15 percent of sunlight into electricity) in the next five years, and have the potential in the long term to reach nearly 50 percent efficiency. Even at the 10-15 percent range, these solar cells would match the performance of the products seen on rooftops today, at a fraction of the cost.

With corresponding advances in electricity storage technologies, this could provide an economically and environmentally attractive pathway to a low-carbon future, fundamentally changing the way society is powered and helping to avert more dangerous climate impacts by eliminating fossil fuels as electricity sources.

What drew you to this field?

As an environmentally-minded scientist, I have always been drawn to the type of research that pushes the boundaries of how society can progress within the limits of the natural world, rather than ignoring these limits. With my background in chemistry and physics, I have had a particular focus on discovering and creating new materials that contribute to a long-standing problem in interesting new ways.

In my previous work at Dalhousie University, I worked on materials for improved battery technologies with Dr. Jeff Dahn, working toward a solution to energy storage for transportation and an increasingly electrified world. While at Dalhousie, Dr. Dahn introduced me to my current supervisor, Dr. Ted Sargent, and I spent a summer working here at the University of Toronto on new materials for solar cells. I was instantly hooked – I could see the potential impact of a solar technology that could capture more energy than current panels, for a lower price than fossil fuels – I couldn't imagine a more exciting, relevant field to join for my PhD.

Why U of T?

I had two top options for grad school; in addition to U of T, Cambridge University in the UK offered me a full scholarship to pursue a PhD. It came down to a choice between pursuing a degree with very high name recognition (Cambridge) or working with the top researcher in the world in the field that interested me the most (novel materials for solar with Professor Sargent here at U of T).

I choose Toronto and have never looked back. As a Canadian, I am proud to see some of the most groundbreaking scientific research in the world taking place here in Canada, and I'm glad I had the opportunity to live and work in my home country while sacrificing absolutely nothing in terms of the experience and expertise I'm gaining.

What advice would you give to a student just starting out in this field?

I'm a bit of an oddity at the moment; I'm pursuing a PhD in Electrical Engineering and Environmental Studies despite having very little formal background in either (I hold a BSc in Chemistry and Physics from Dalhousie). Despite that, I'm having a great time; I'm learning a lot and still contributing at the highest level to a truly cutting-edge topic.

Given all that, my general advice would be twofold: first, if you have the time during undergraduate studies, try to get some hands-on experience with a research group – more than any class, this will show you what you enjoy, what you're good at, and what you're passionate about. It also shows potential supervisors that you're interested in and have an aptitude for real research. I met Professor Sargent through a summer undergraduate research project - that summer really seeded my excitement about the field and also provided me with a supervisor at U of T already well acquainted with my work ethic and enthusiasm who could vouch for me throughout the graduate application process.

Second, follow what excites you. In a world of increasing interdisciplinarity, there will almost inevitably be a way to apply what you know and what you've learned to a research topic that you're truly interested in. When in doubt, ask to chat with a researcher about their field and how you could contribute; in my experience they will be just as excited about the research as you are, and will be happy to help you find your way.