About
We advance the modeling, characterization, and control of defects in solar cells and the development of new materials and device architectures for solar energy storage.
Research topics
- Materials science
- Nanotechnology
- Optoelectronics
- Chemistry
- Chemical engineering
- Composite material
- Geology
- Environmental science
- Inorganic chemistry
- Engineering
- Electrical engineering
- Crystallography
Selected publications
Surface reaction for efficient and stable inverted perovskite solar cells
Nature · 2022 · 1099 citations
- Materials science
- Nanotechnology
- Chemical engineering
ACS Applied Materials & Interfaces · 2021 · 56 citations
- Materials science
- Composite material
- Nanotechnology
The mechanical properties of π-conjugated (semiconducting) polymers are a key determinant of the stability and manufacturability of devices envisioned for applications in energy and healthcare. These properties─including modulus, extensibility, toughness, and strength─are influenced by the morphology of the solid film, which depends on the method of processing. To date, the majority of work done on the mechanical properties of semiconducting polymers has been performed on films deposited by spin coating, a process not amenable to the manufacturing of large-area films. Here, we compare the mechanical properties of thin films of regioregular poly(3-heptylthiophene) (P3HpT) produced by three scalable deposition processes─interfacial spreading, solution shearing, and spray coating─and spin coating (as a reference). Our results lead to four principal conclusions. (1) Spray-coated films have poor mechanical robustness due to defects and inhomogeneous thickness. (2) Sheared films show the highest modulus, strength, and toughness, likely resulting from a decrease in free volume. (3) Interfacially spread films show a lower modulus but greater fracture strain than spin-coated films. (4) The trends observed in the tensile behavior of films cast using different deposition processes held true for both P3HpT and poly(3-butylthiophene) (P3BT), an analogue with a higher glass transition temperature. Grazing incidence X-ray diffraction and ultraviolet-visible spectroscopy reveal many notable differences in the solid structures of P3HpT films generated by all four processes. While these morphological differences provide possible explanations for differences in the electronic properties (hole mobility), we find that the mechanical properties of the film are dominated by the free volume and surface topography. In field-effect transistors, spread films had mobilities more than 1 magnitude greater than any other films, likely due to a relatively high proportion of edge-on texturing and long coherence length in the crystalline domains. Overall, spread films offer the best combination of deformability and charge-transport properties.
A fabrication process for flexible single-crystal perovskite devices
Nature · 2020 · 425 citations
- Materials science
- Optoelectronics
- Nanotechnology
Joule · 2020 · 268 citations
- Materials science
- Environmental science
- Inorganic chemistry
Recent grants
Frequent coauthors
- 91 shared
Mariana I. Bertoni
Arizona State University
- 73 shared
Tonio Buonassisi
Massachusetts Institute of Technology
- 58 shared
Rishi E. Kumar
Lawrence Berkeley National Laboratory
- 51 shared
Barry Lai
- 46 shared
Jasmin Hofstetter
1366 Technologies (United States)
- 31 shared
Rico Meier
Arizona State University
- 25 shared
Yanqi Luo
Argonne National Laboratory
- 25 shared
Tala Sidawi
University of California, San Diego
Labs
Education
- 2005
Ph.D., Physics
University of California, San Diego
- 2002
M.S., Physics
University of California, San Diego
- 2000
B.S., Physics
University of California, San Diego
Awards & honors
- Gareth Thomas Materials Excellence Award
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