Anisotropic Singlet Fission in Single Crystalline Hexacene

Area of Science:

• Materials Science
• Physical Chemistry
• Photovoltaics

Background:

• Singlet fission is a process that can improve solar energy conversion by overcoming the Shockley-Queisser limit.
• The key steps in singlet fission, triplet pair formation and quantum decoherence, are not fully understood.
• Understanding these mechanisms is crucial for developing next-generation solar cells.

Purpose of the Study:

• To investigate the mechanisms of triplet pair formation and quantum decoherence in singlet fission.
• To examine the anisotropy of singlet fission rates in single crystalline hexacene.
• To elucidate the factors contributing to directional differences in singlet fission.

Main Methods:

• Experimental investigation of singlet fission in single crystalline hexacene.
• Theoretical analysis using Redfield quantum dissipation theory.
• Hybrid experimental/theoretical framework to analyze triplet pair dynamics.

Main Results:

• Observed remarkable anisotropy of the singlet fission rate along different crystal axes in hexacene.
• Determined that triplet pair formation occurs on a similar timescale along both crystal axes.
• Identified quantum decoherence as the likely cause of the observed directional anisotropy.
• Found distinct quantum decoherence rates linked to energy loss differences, explained by Redfield theory.

Conclusions:

• Quantum decoherence plays a critical role in the anisotropic singlet fission observed in hexacene.
• The energy loss associated with decoherence differs significantly between crystal axes.
• This research advances the understanding of singlet fission mechanisms.
• Provides insights for designing new materials for efficient third-generation solar cells.