Photoinduced electron-transfer distance is controlled by the driving force in solid-state organic donor-acceptor...

Area of Science:

• Photovoltaics and Renewable Energy
• Materials Science
• Physical Chemistry

Background:

• Understanding photocurrent generation in organic solar cells (OSCs) is crucial for improving their efficiency.
• The relationship between photochemical driving force and charge-transfer dynamics has been a complex area of research.

Purpose of the Study:

• To investigate the interplay between driving force and charge-separation distances in OSCs.
• To determine the optimal photochemical driving force for maximizing solar cell efficiencies.
• To elucidate the factors controlling efficient charge separation and minimize voltage losses.

Main Methods:

• Utilized photoinduced absorption-detected magnetic resonance (PADMR) to measure average charge-separation distances.
• Employed time-resolved microwave conductivity (TRMC) to quantify free charge yields.
• Analyzed dilute donor-acceptor blends across varying driving forces.

Main Results:

• Found that higher driving forces lead to shorter charge-separation distances.
• Observed suppressed free-carrier generation at large driving forces.
• Demonstrated that the dielectric constant of the material dictates the minimum driving force for efficient charge separation.

Conclusions:

• Supported a long-range electron-transfer model where driving force influences initial electron-hole pair delocalization.
• Highlighted that optimal efficiency is achieved by skipping the shortest-range charge-transfer states.
• Identified the material's dielectric constant as the key factor setting the minimum driving force for efficient charge separation and reduced voltage losses.