Infrared Electro-Optical Spectroscopy of Degradation Pathways in Organo-Halide Perovskite Photovoltaics

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With this award, the Chemical Structure, Dynamics, and Mechanisms (CSDM-A) Program of the Division of Chemistry is supporting Professor John Asbury at Penn State University to use Fourier transform infrared spectroscopy combined with electrical techniques to examine the chemical origins of defects in an emerging class of photovoltaic materials known as organo-halide perovskites. These photovoltaic materials represent a promising class of potentially inexpensive and highly efficient solar cells - a high priority for development of a sustainable energy economy that does not rely on fossil fuels. However, the long-term stability of these materials is limited by the formation of defects. The use of electrical techniques combined with infrared spectroscopy enables the identification of chemical species that cause the defects. This information in turn can guide the development of synthetic strategies to eliminate defects, resulting in more stable and higher efficiency solar cells. The PI also plans to engage underrepresented middle school and high school students in this research project through the use of solar cell models by which they will use the scientific process of hypothesis, experiment and evaluation to explore possible solutions to scientific challenges that have direct bearing on solar energy technologies.The technical objective of this project is to examine charge-trapping in organo-halide perovskites using infrared-detected admittance spectroscopy that combines electrical information about charge trap energetic distributions with structural information about the molecular species that give rise to those traps from Fourier transform infrared spectroscopy. Traditional electrical characterization techniques provide information about the density and energetic distribution of charge traps in materials but do not reveal structural information about the chemical origins of such traps. While Fourier transform infrared spectroscopy can provide structural information about materials through measurement of their vibrational frequencies, this technique typically measures the majority component of a material and is not able to capture the vibrational spectra of defects, which represent a minority component. By combining these techniques, this project will provide direct measurements of charge trap energetic distributions and densities along with structural information about the chemical species that give rise to those defects. Systematic variation of the chemical structure, composition, and preparation of organo-halide perovskite photovoltaic materials will enable fundamental understanding of how the electronic structure of these promising materials depends on their underlying chemical and morphological properties. These measurements seek to address key scientific challenges that are important for realizing more efficient and stable perovskite solar cells.