The tools of synthetic chemistry allow us to fine-tune molecules at a level of precision not yet accessible with inorganic solids. We have investigated hybrids that couple molecules to the superior mechanical and optoelectronic properties of solids. Recently, a class of hybrid materials called lead-iodide perovskites has been identified as extremely promising absorbers for low-cost and high-efficiency solar cells. Impressively, efficiencies of solar cells employing these perovskite absorbers have reached commercially viable values in just six years. Despite this remarkable progress in device manufacture, the materials’ inherent instability and toxicity may impede their large-scale use. In this talk, I will discuss the sources of these problems and our efforts at overcoming them using synthetic chemistry. The material’s extreme water sensitivity is a problem for large-scale device fabrication and their long-term use. The toxicity of lead is also a primary concern for the wide-scale use of this technology, particularly in light of the material’s water solubility, which greatly increases contamination risks. I will present new materials synthesized in our labs to address these issues. I will also discuss transient, light-induced changes that occur in these materials, which impede high voltages from being realized in perovskite devices. I will suggest methods to mitigate these effects, including the application of pressure to change the photophysical properties of these compressible solids.
Hema Karunadasa is an assistant professor in Chemistry at Stanford University. She performed undergraduate research in solid-state chemistry with Robert Cava at Princeton University synthesizing geometrically frustrated magnets. She worked with Jeffrey Long at UC Berkeley for her doctoral research on magnetic molecules and molecular catalysts for generating hydrogen from water. She continued these studies as a postdoc at the Lawrence Berkeley National Laboratory with Christopher Chang and Jeffrey Long. She then worked with Harry Gray at Caltech studying molecular catalysts for hydrocarbon oxidation. She joined the Chemistry faculty at Stanford University in 2012. Her research aims to bridge molecular and solid-state chemistry. Her group uses solution-state methods to design hybrids that realize the advantages of molecules and extended inorganic solids in a single material. They target materials for various applications in clean energy: absorbers for solar cells, electrodes for rechargeable batteries, phosphors for solid-state lighting, and sorbents for atmospheric pollutants. She has received the NSF CAREER award, the Sloan Fellowship, and the Stanford Terman and Gabilan Fellowships.