Charge transfer dynamics in polymer-fullerene blends for efficient solar cells

Area of Science:

• Organic electronics
• Photovoltaics
• Materials science

Background:

• Bulk heterojunction solar cells utilize blends of donor and acceptor materials.
• Poly(3-hexylthiophene) (P3HT) and fullerene derivatives like PCBM are common components.
• BisPCBM offers potential performance enhancements over PCBM in P3HT blends.

Purpose of the Study:

• To investigate the reasons for reduced short-circuit current in P3HT:bisPCBM blends compared to P3HT:PCBM.
• To determine if the reduced open-circuit voltage or altered morphology impacts performance.
• To elucidate the relationship between microstructure and electron transfer dynamics.

Main Methods:

• Fabrication of bulk heterojunction thin films using P3HT:PCBM and P3HT:bisPCBM blends.
• Analysis of photoluminescence dynamics in both solution and thin-film states.
• Correlation of photoluminescence dynamics with material microstructure and energy level offsets.

Main Results:

• P3HT:bisPCBM blends exhibit higher open-circuit voltage but lower short-circuit current than P3HT:PCBM.
• In solution, photoluminescence dynamics are similar, indicating homogeneous donor-acceptor distribution.
• In thin films, P3HT:bisPCBM shows slower photoluminescence dynamics, suggesting altered microstructure.

Conclusions:

• The reduced electron transfer efficiency in P3HT:bisPCBM is attributed to microstructural differences, not the 100 meV reduction in LUMO offset.
• Morphology plays a critical role in the photoluminescence dynamics and performance of bulk heterojunction solar cells.
• Optimizing the microstructure of P3HT:bisPCBM blends is key for improving solar cell efficiency.