Multiphonon relaxation slows singlet fission in crystalline hexacene
Erik Busby1, Timothy C Berkelbach, Bharat Kumar
1Energy Frontier Research Center, ¶Department of Chemistry, and §Departments of Physics and Electrical Engineering, Columbia University , New York, New York 10027, United States.
Journal of the American Chemical Society
|July 2, 2014
Summary
Singlet fission in hexacene crystals occurs in 530 fs, offering insights into acene material design for enhanced solar-cell efficiency. This study elucidates mechanistic trends in singlet fission rates.
Area of Science:
- Materials Science
- Photochemistry
- Organic Electronics
Background:
- Singlet fission (SF) is a process converting one singlet excitation into two triplet excitations.
- SF is a promising strategy for boosting solar cell efficiency.
- Understanding SF mechanisms is crucial for designing new materials.
Purpose of the Study:
- Investigate SF in crystalline hexacene to understand mechanistic trends.
- Compare SF rates across the acene family (pentacene, tetracene, hexacene).
- Develop a theoretical framework for SF rates.
Main Methods:
- Characterization of static and transient optical absorption in hexacene.
- Theoretical analysis of electronic couplings and SF rates.
- Microscopic theory development.
Main Results:
- Hexacene exhibits a SF time scale of 530 fs.
- Hexacene's SF is significantly faster than tetracene (10-100 ps) but slower than pentacene (80-110 fs).
- A multiphonon relaxation effect due to large exothermicity explains hexacene's SF rate.
Conclusions:
- SF mechanistic trends can be elucidated by studying the acene family.
- The developed microscopic theory quantitatively predicts SF rates in acenes.
- Findings provide a foundation for rational design of SF materials for solar energy applications.
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