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'Rising star' set to shine with GCEP research
Hemamala Karunadasa

Hemamala Karunadasa is an assistant professor in chemistry at Stanford University. She is also co-principal investigator with Michael McGehee, a professor in materials science and engineering, on the GCEP effort, "Novel Inorganic-Organic Perovskites for Solution Processable Photovoltaics." She recently shared highlights of her work at the GCEP Research Symposium.

In July 2014, Karunadasa was honored as a "Rising Star" at the 41st International Conference of Coordination Chemistry (ICCC) in Singapore. The award is given to those "who are already internationally recognizable figures even at this early-stage of their research career, who are actively pushing and making an impact in new and important domains in coordination chemistry, and have an exponential upward projectile in their research profile."

Earlier this year, she received a National Science Foundation (NSF) CAREER award for her work, "Small-Molecule Capture and Ion Transport in Well-Defined Hybrid Materials." This five-year NSF award supports the early-career development of junior faculty so they can build a "firm foundation for a lifetime of integrated contributions to research and education."

Before joining the Stanford Faculty in 2012, Karunadasa worked as a postdoctoral researcher with Harry Gray (a former GCEP investigator) at the California Institute of Technology conducting research on molecular catalysts for hydrocarbon oxidation. Prior to that, she was a postdoctoral researcher at the University of California–Berkeley and the Lawrence Berkeley National Laboratory.

Karunadasa received her A.B. degree in chemistry from Princeton University and her Ph.D. in inorganic chemistry from the University of California–Berkeley.

She took some time to answer a few questions for us:

Please describe your GCEP research and how it could potentially lead to significantly lower greenhouse gas emissions.

Ian Smith and Hemamala Karunadasa
Stanford assistant professor Hemamala Karunadasa (right) and graduate student Ian Smith discuss the film quality of lead-iodide perovskite absorbers.

My group aims to design hybrids that combine the advantages of organic and inorganic components in a single material. Our GCEP research is focused on addressing the major shortcomings of lead-iodide hybrid perovskites for photovoltaic applications. These materials have recently emerged as extremely promising absorbers for low-cost and high-efficiency solar cells. However, the toxicity of lead and the moisture sensitivity of the material will likely impede its wide-scale use. We have research projects on both improving the moisture resistance of lead-based perovskites, and on finding nontoxic analogs with similar photophysical properties. For example, my student Ian Smith recently synthesized an organic-inorganic layered lead-iodide perovskite absorber with greatly improved moisture resistance. He accomplished this by using hydrophobic organic layers to repel moisture, while the inorganic layers absorb sunlight to produce photocurrent.

What are perovskites and why are researchers excited about their use in photovoltaic research?

Glove Box
GCEP investigator Hemamala Karunadasa (right) watches graduate student Abraham Saldivar prepare a solution for making the perovskites.

Perovskites are a broad class of solids that range from insulators to high-temperature super conductors. Three-dimensional perovskites contain an extended inorganic framework of corner-sharing octahedra. This framework has a negative charge, which is balanced by small positive ions that reside in the cavities of the structure. The hybrid perovskites used in solar cells contain a lead-iodide framework with positively charged organic molecules providing charge balance.

Although perovskites have been known for many years, the unusual properties of organic-inorganic metal-halide perovskites for sunlight absorption and charge transport have only recently come to light. Furthermore, unlike most other perovskites, these hybrid materials form from solution, which enables inexpensive and scalable processing. These materials are also highly crystalline, which allows us to use X-ray diffraction techniques to probe their structure. Researchers are still trying to understand why these materials are so efficient at absorbing sunlight and transporting charge carriers.

How does the interdisciplinary relationship between members of your chemistry lab and those in co-PI Michael McGehee’s engineering group benefit your GCEP research?

Item Tray
Perovskite films of high quality and improved moisture resistance are being created in the Karunadasa lab.

Our collaboration has really accelerated this research. Researchers move freely between the two labs. The synthetic work and material characterization is mostly conducted in my lab, and further photophysical characterization and device construction is performed in Mike’s lab. Through this collaboration, we have learned a lot about solar cells and the importance of characterizing our materials under operating conditions in a device. Mike’s group has learned about the materials properties of perovskites and synthetic handles for tuning their structure. This has helped us launch a multipronged attack on improving perovskite solar cells. The students in both groups have led this effort and deserve most of the credit for our early successes.

As a postdoctoral researcher, you worked with chemistry legend Harry Gray at Caltech from 2010 - 2012. How did that influence your career path?

I delayed my start date at Stanford so that I could work with Harry and it was a transformative experience. I was constantly amazed at how he could talk in depth about any research topic that came to my mind. He could explain his profound insights into chemistry with so much humor that I could easily spend hours in his office.

Yes, I join a long list of people whose careers have been influenced by Harry. His research program highlights the reach of Inorganic Chemistry in areas as diverse as proteins, small molecules, and nanoparticles, and I love the fact that he is always ready to try something new. Through his influence, I try to venture into unfamiliar research areas using the tools of inorganic chemistry. Harry is also an excellent role model for showing that you can do great work and not take yourself too seriously.

When did you realize that you had an interest in chemistry?
I always liked my undergrad chemistry classes, but I did not love Chemistry until I started research in the Cava lab at Princeton. As part of my undergrad research, I synthesized metal-oxide perovskites. (Unlike metal-halide perovskites that form at room temperature, these syntheses required temperatures of about 1500°C). Bob Cava’s enthusiasm for solid-state materials was so contagious that after receiving my Ph.D. in molecular chemistry, I have now returned to perovskites.

Hemamala's team photo
Stanford assistant professor Hemamala Karunadasa (center) with members of her research group.

What would surprise readers about you or your research? The foundation for my group’s work on hybrid perovskites was laid when I was a second-year graduate student. Although my research focus was on magnetic molecules, as part of my Ph.D. qualifying exam I had to write an original research proposal. After an intensive literature search, I stumbled upon two-dimensional hybrid perovskites. I was struck by their beautiful crystal structures and their potential for combining the very different properties of organic and inorganic materials. I decided that if I was ever lucky enough to have my own research group, I would return to these materials.

What do you find most rewarding about your work at Stanford?
Working with students in chemistry and in other departments.

Any advice for young people considering careers in chemistry?
It’s a great life – you get paid to work on what excites you most. A research career requires dedication, but nothing beats the thrill of seeing your ideas work.

Starting a research group takes hard work, but also some faith. I don’t think anyone really feels ready for this job. You just have to plunge in and believe that you and your students can learn on the job.

GCEP Research: Novel Inorganic-Organic Perovskites for Solution Processable Photovoltaics

A Layered Hybrid Perovskite Solar-Cell Absorber with Enhanced Moisture Stability
Ian C. Smith, Dr. Eric T. Hoke, Dr. Diego Solis-Ibarra, Prof. Michael D. McGehee and Prof. Hemamala I. Karunadasa (Article first published online: September 4, 2014)

Photos by Maxine Lym



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