[Paper Review] Multiple Quintets via Singlet Fission in Ordered Films at Room Temperature

Daphné Lubert‐Perquel, Salvadori, Enrico+7 more|arXiv (Cornell University)|Jan 2, 2018

Organic Electronics and Photovoltaics40 references41 citations

TL;DR

The paper demonstrates formation of distinct quintet excitons at room temperature in ordered solid solutions of pentacene in p-terphenyl, linked to specific pentacene dimer geometries identified via angular dependence using EPR spectroscopy.

ABSTRACT

The growing interest in harnessing singlet fission for photovoltaic applications stems from the possibility of generating two excitons from a single photon. Quantum efficiencies above unity have been reported, yet the correlation between singlet fission and intermolecular geometry is poorly understood. To address this, we investigated ordered solid solutions of pentacene in p-terphenyl grown by organic molecular beam deposition. Two classes of dimers are expected from the crystal structure - parallel and herringbone - with intrinsically distinctive electronic coupling. Using electron paramagnetic resonance spectroscopy, we provide compelling evidence for the formation of distinct quintet excitons at room temperature. These are assigned to specific pentacene pairs according to their angular dependence. This work highlights the importance of controlling the intermolecular geometry and the need to develop adequate theoretical models to account for the relationship between structure and electronic interactions in strongly-coupled, high-spin molecular systems.

Motivation & Objective

• Motivate understanding of how intermolecular geometry affects singlet fission efficiency and high-spin exciton formation in solid-state films.
• Investigate ordered solid solutions of pentacene in p-terphenyl grown by organic molecular beam deposition.
• Identify and assign distinct quintet excitons to specific pentacene pair geometries (parallel vs. herringbone) using spectroscopic evidence.

Proposed method

• Grow ordered pentacene:p-terphenyl solid solutions via organic molecular beam deposition.
• Use electron paramagnetic resonance spectroscopy to probe spin states and exciton formation.
• Analyze angular dependence of signals to assign quintet excitons to specific pentacene dimer geometries.

Experimental results

Research questions

• RQ1 Can room-temperature quintet excitons form via singlet fission in ordered pentacene:p-terphenyl films?
• RQ2 How do parallel and herringbone dimer geometries influence electronic coupling and quintet formation?
• RQ3 Can angular dependence in EPR distinguish among different pentacene-pair configurations?

Key findings

• Compelling evidence for distinct room-temperature quintet excitons formed via singlet fission.
• Quintet excitons are assignable to specific pentacene pairs based on angular dependence.
• Intermolecular geometry (parallel vs. herringbone) critically influences electronic coupling and high-spin state formation.