Surface Loading Dictates Triplet Production via Singlet Fission in Anthradithiophene Sensitized TiO₂ Films

Area of Science:

• Photovoltaics and Renewable Energy
• Materials Science
• Physical Chemistry

Background:

• Singlet fission (SF) converts one high-energy singlet excited state into two lower-energy triplet excited states.
• SF is a promising strategy to enhance dye-sensitized solar cell (DSSC) efficiency.
• Controlling dye orientation on mesoporous metal oxide surfaces is crucial for maximizing SF and minimizing deactivation.

Purpose of the Study:

• Investigate the effect of dye surface coverage and anchoring groups on SF in DSSCs.
• Understand molecular interactions at mesoporous interfaces to optimize triplet excited-state generation.
• Determine optimal dye loading for efficient singlet fission in anthradithiophene-based DSSCs.

Main Methods:

• Synthesized two anthradithiophene dyes with one or two carboxylic acid anchoring groups.
• Varied dye concentration in loading solutions for deposition onto mesoporous metal oxide surfaces.
• Employed ultrafast transient absorption spectroscopy to study photophysics and excited-state dynamics.

Main Results:

• Increased surface coverage of single-carboxylic acid functionalized dyes enhanced triplet excited-state growth via singlet fission.
• Increased surface coverage of dual-carboxylic acid functionalized dyes did not show a similar enhancement in triplet growth.
• Dye orientation and intermolecular interactions significantly influence singlet fission efficiency at the interface.

Conclusions:

• Dye surface coverage and the number of anchoring groups critically affect singlet fission efficiency in DSSCs.
• Single carboxylic acid groups promote beneficial molecular arrangements for singlet fission compared to dual groups.
• This work provides insights into controlling interfacial molecular interactions for improved solar cell performance.