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Photoinduced charge generation in a molecular bulk heterojunction material
Loren G Kaake1, Jacek J Jasieniak, Ronald C Bakus
1Center for Polymers and Organic Solids, University of California-Santa Barbara, Santa Barbara, California 93106, United States. lkaake@physics.ucsb.edu
Journal of the American Chemical Society
|November 8, 2012
Summary
Charge carriers in organic photovoltaics are generated within 100 femtoseconds due to excited state delocalization. This ultrafast process, observed in both molecular and polymer bulk heterojunctions, is key to improving device efficiency.
Area of Science:
- Organic electronics
- Photovoltaics
- Spectroscopy
Background:
- Understanding charge generation is crucial for enhancing organic photovoltaic (OPV) device efficiency.
- Despite extensive research, a complete model for charge generation and recombination in OPVs is still developing.
Purpose of the Study:
- To investigate ultrafast charge photogeneration and recombination dynamics in high-performing organic photovoltaic bulk heterojunction (BHJ) blends.
- To compare these dynamics in solution-processed molecular BHJ and polymer-based BHJ materials.
Main Methods:
- Ultrafast transient absorption spectroscopy.
- Polarization anisotropy measurements.
- Study of pure films of solution-processed molecular BHJ.
Main Results:
- Majority of charge carriers generated in <100 fs in both molecular and polymer BHJs.
- Excited state delocalization is identified as the mechanism for ultrafast charge transfer.
- Exciton diffusion to heterojunctions observed between 1-500 ps.
- Pure molecular films show prompt delocalized charge production (t < 100 fs) dominated by molecular excitons.
Conclusions:
- Ultrafast charge generation (<100 fs) is a key feature in high-performing organic BHJs, driven by excited state delocalization.
- Exciton diffusion plays a role at longer timescales.
- Findings provide insights for designing more efficient organic photovoltaic materials.
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