Device-Based Probe of Triplet Exciton Diffusion in Singlet Fission Materials

Area of Science:

• Organic electronics
• Photophysics
• Materials science

Background:

• Singlet fission materials enable efficient charge generation but understanding triplet transport is crucial.
• Directly measuring triplet diffusion length (L_D) is challenging due to competing processes.
• Organic semiconductors are key components in next-generation solar cells and optoelectronic devices.

Purpose of the Study:

• To develop and validate a device-based method for quantifying intrinsic triplet diffusion length (L_D) in singlet fission organic semiconductors.
• To overcome the limitations of existing techniques that struggle to isolate triplet transport.
• To provide accurate L_D values for archetypal singlet fission materials.

Main Methods:

• Optical injection of triplet excitons into singlet fission materials via energy transfer from a spin-orbit coupled layer.
• Device fabrication with varying layer thicknesses to control triplet migration distance.
• Analysis of photocurrent ratios from injector and acceptor layers to decouple L_D from other efficiencies.
• Modeling triplet dissociation at a donor-acceptor interface.

Main Results:

• A novel device-based method successfully measured the intrinsic triplet diffusion length (L_D).
• Significant variation in L_D was observed across different archetypal singlet fission materials.
• Measured L_D values ranged from 3.3 ± 0.4 nm (5,12-bis((triisopropylsilyl)ethynyl)tetracene) to 17.1 ± 1.3 nm (pentacene) and 32.1 ± 2.6 nm (tetracene).

Conclusions:

• The developed method provides a reliable way to extract triplet diffusion length, independent of singlet fission efficiency.
• The wide range of L_D values highlights the importance of material-specific optimization for triplet harvesting.
• Accurate L_D data is essential for designing efficient organic electronic devices based on singlet fission.