Mechanistic Study of Charge Separation in a Nonfullerene Organic Donor-Acceptor Blend Using Multispectral...

Area of Science:

• Materials Science
• Photovoltaics
• Spectroscopy

Background:

• Organic photovoltaics (OPVs) with nonfullerene acceptors achieve high efficiencies.
• Efficient charge separation at donor-acceptor interfaces is crucial for OPV performance.
• Mechanisms of charge separation in OPVs remain incompletely understood due to limited spectroscopic probes.

Purpose of the Study:

• Investigate the charge separation mechanisms in a model OPV system.
• Elucidate the role of interfacial energetics and dynamics in efficient charge transfer.
• Provide insights for enhancing power conversion efficiencies in organic solar cells.

Main Methods:

• Utilized multidimensional spectroscopy across visible to mid-infrared ranges.
• Studied a model system comprising PBDB-T (donor) and ITIC (acceptor).
• Analyzed transient dynamics of charge carriers at the donor-acceptor heterojunction.

Main Results:

• Identified bound polaron pairs (BPPs) within acceptor domains as critical for hole transfer.
• Observed rapid transition of BPPs to delocalized polarons within 100 femtoseconds.
• Demonstrated that weak electron-hole binding and polaron delocalization enable efficient charge separation at low driving forces.

Conclusions:

• Bound polaron pairs are essential for efficient charge separation in nonfullerene acceptor-based OPVs.
• Understanding polaron dynamics offers a pathway to optimize OPV power conversion efficiency.
• The findings provide fundamental insights into interfacial charge transfer processes in organic electronics.