Dichotomous Initial Exciton Conversion at a DPP2Py2T-PCBM Interface: Insights from Embedded GW-Bethe-Salpeter...

Area of Science:

• Materials Science
• Computational Chemistry
• Physical Chemistry

Background:

• Organic solar cells (OSCs) exhibit varying charge generation efficiencies based on initial photoexcitation.
• Understanding the dynamics of exciton conversion is crucial for optimizing OSC performance.

Purpose of the Study:

• Investigate the origin of efficiency differences in OSCs based on donor or acceptor photoexcitation.
• Elucidate the mechanisms of charge generation through simulations of localized to charge-transfer (CT) excitation dynamics.

Main Methods:

• Quantum-quantum-classical embedded GW-Bethe-Salpeter equation simulations.
• Calculation of excitonic energy levels, electronic couplings, and reorganization energies.
• Application of Marcus theory and population dynamics modeling.

Main Results:

• Identified multiple CT-type excitations with varying characters.
• Determined a 0.30 eV separation between relevant lowest integer CT excitations.
• Found significantly higher activation barriers for polymer LE (0.25 eV) compared to fullerene LE (0.05 eV).
• Demonstrated donor excitation preference for higher CT states with lower binding energy.

Conclusions:

• The dichotomy in charge generation efficiency stems from differing activation barriers for CT state formation.
• Donor photoexcitation favors less bound CT states, facilitating faster charge separation within picoseconds.
• Simulation results provide insights into optimizing exciton dynamics for improved OSC performance.