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Spatiotemporal Spectroscopy of Fast Excited-State Diffusion in 2D Covalent Organic Framework Thin Films.
Laura Spies1, Alexander Biewald1, Laura Fuchs2
1Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU), Butenandtstraße 5-13, Munich 81377, Germany.
Journal of the American Chemical Society
|January 2, 2025
Summary
Covalent organic frameworks (COFs) exhibit efficient exciton diffusion for sustainable energy. This study reveals high diffusion coefficients and lengths in 2D WBDT COF films, driven by both hopping and band-like transport.
Area of Science:
- Materials Science
- Organic Chemistry
- Physical Chemistry
Background:
- Covalent organic frameworks (COFs) are crystalline, porous materials with potential in sustainable energy applications.
- Their unique structure combines molecular and solid-state properties, enabling efficient charge transport.
- Studying photoexcited charge carrier diffusion in COFs is crucial for optimizing their performance.
Purpose of the Study:
- Investigate charge carrier diffusion in a 2D WBDT COF thin film.
- Characterize the spatiotemporal evolution of photogenerated excited states.
- Understand the mechanisms governing exciton transport.
Main Methods:
- Remote-detected time-resolved photoluminescence (RDTR PL) measurements.
- Optical pump terahertz probe (OPTP) studies.
- Theoretical simulations and temperature-dependent transport analysis.
Main Results:
- Identified two diffusive species: short-lived free carriers and long-lived excitons.
- Observed high lateral exciton diffusion coefficients (up to 4 cm²/s at 200 K) and diffusion lengths of hundreds of nanometers.
- Exciton transport involves both incoherent hopping and coherent band-like mechanisms.
Conclusions:
- The 2D WBDT COF thin film facilitates efficient exciton diffusion across grain boundaries.
- Both order and disorder significantly impact charge carrier diffusion in COFs.
- These findings provide insights for designing COFs for advanced energy applications.
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