Vibronically assisted sub-cycle charge transfer at a non-fullerene acceptor heterojunction

Area of Science:

• Materials Science
• Physical Chemistry
• Organic Electronics

Background:

• Excited-state charge transfer is crucial for organic photovoltaics, photocatalysis, and photodetection.
• Traditional models require large energy offsets and strong coupling, limiting device performance.
• Investigating new pathways for efficient charge transfer is essential.

Purpose of the Study:

• To investigate ultrafast charge transfer in polymer non-fullerene-acceptor heterojunctions with minimal energy offset.
• To understand the role of vibrational modes in facilitating rapid charge transfer.
• To explore mechanisms for efficient charge transfer beyond traditional requirements.

Main Methods:

• Fabrication of model heterojunctions with covalently tethered perylene diimide acceptors and low-bandgap polymer donors.
• Spectroscopic analysis to determine charge-transfer timescales and vibrational dynamics.
• Computational modeling to identify driving vibrational modes.

Main Results:

• Achieved an ultrafast charge-transfer timescale of approximately 18 femtoseconds.
• Observed the launch of coherent wavepackets on the non-fullerene acceptor's potential energy surface.
• Identified specific polymer-centered vibrational modes that enable rapid charge transfer by mixing exciton and charge-transfer states.

Conclusions:

• Ultrafast charge transfer is achievable even with small energy offsets and weak coupling.
• High-frequency vibrational modes play a critical role in driving rapid charge transfer.
• Findings offer new strategies for designing high-performance organic electronic devices.