Unraveling Ultrafast Charge Transfer Dynamics in Organic Solar Cells
Yifan Dong
National Renewable Energy Lab
Friday, March 22, 12:00 PM, C215 ESC
Abstract:
Photoinduced charge transfer mechanisms are central to solar energy conversion processes including photosynthesis and photovoltaics. In this talk, I will discuss how time-resolved optical spectroscopy can allow us to understand the underlying photophysical mechanisms in organic solar cells (OSCs), with a particular focus on the charge-transfer states formed from an electron-donating to an electron accepting molecular entity. Firstly, I will discuss the origin of the formation of bound charge-transfer states in polymer:non-fullerene systems, which is a key loss pathway of such OSCs. Using transient absorption and pump push photocurrent spectroscopies, a photophysical model describing charge separation and recombination processes in these low-offset archetypal systems will be presented. This will be followed by discussions on effective ways to suppress such recombination losses. Secondly, I will talk about the inverted energy gap law correlation between charge-transfer state lifetimes and material energetics in a wide range of stateof-the-art polymer:non-fullerene systems. From these observations, I will propose strategies to further enhance efficiencies via extending exciton lifetimes of non-fullerene acceptors. Thirdly, I will talk about how tuning the molecular orientations can drive efficient charge generation in low dielectric organic small molecules. Such molecular engineering paves the way for future OSC development.
References
1 Dong, Y. et al. The binding energy and dynamics of charge-transfer states in organic photovoltaics with low driving force for charge separation. The Journal of Chemical Physics 150, 104704 (2019). https://doi.org:10.1063/1.5079285
2 Dong, Y. et al. Correlating Charge-Transfer State Lifetimes with Material Energetics in Polymer:Non-Fullerene Acceptor Organic Solar Cells. Journal of the American Chemical Society 143, 7599-7603 (2021). https://doi.org:10.1021/jacs.1c00584
3 Dong, Y. et al. Orientation dependent molecular electrostatics drives efficient charge generation in homojunction organic solar cells. Nature Communications 11, 4617 (2020). https://doi.org/10.1038/s41467-020-18439-z
Biographical Sketch:
Yifan Dong is currently a postdoctoral researcher at National Renewable Energy Lab (NREL) working with Dr. Matthew Beard. Her research focuses on using ultrafast optical and terahertz spectroscopy to study charge and spin dynamics in chemical systems. She is interested in studying light-matter interactions over ultrafast timescales to elucidate design principles that will facilitate technological development. Prior to NREL, Yifan earned her doctorate in 2021 from Imperial College London under the supervision of Prof. James Durrant and Prof. Artem Bakulin to investigate charge generation and recombination dynamics in organic photovoltaics and photodetectors using ultrafast optical and optoelectronic spectroscopy.
Daniel James
Utah Valley University
Friday, March 29, 12:00 PM, C215 ESC
Abstract:
Biographical Sketch:
John Gardiner
Wall Street
Friday, April 12, 12:00 PM, C215 ESC
Abstract:
Biographical Sketch:
We welcome anyone who wish to attend, and typically serve refreshments ten minutes before the colloquium begins. Speakers generally keep their presentation accessible to undergraduate physics students.