Intensity Dependent Femtosecond Dynamics in a PBDTTPD-Based Solar Cell Material

Area of Science:

• Materials Science
• Photovoltaics
• Polymer Chemistry

Background:

• Conjugated polymers like PBDTTPD are key components in organic solar cells (OSCs).
• Fullerene derivatives, such as PCBM, are commonly used as electron acceptors in OSCs.
• Understanding excited state dynamics is crucial for optimizing OSC performance.

Purpose of the Study:

• To investigate the excited state dynamics of pristine PBDTTPD.
• To analyze the ultrafast evolution of charge carriers in PBDTTPD:PCBM blends.
• To determine the factors affecting charge carrier yield and recombination.

Main Methods:

• Femtosecond transient absorption spectroscopy was employed.
• Studies were conducted on both pristine PBDTTPD thin films and PBDTTPD:PCBM bulk heterojunction blends.
• Varying laser fluences were used to study annihilation effects.

Main Results:

• Charge carrier generation was observed within 100 femtoseconds in PBDTTPD:PCBM blends.
• Charge separation dynamics were followed on a picosecond timescale.
• Exciton-exciton and exciton-charge annihilation were found to reduce charge carrier yield at high laser fluences.
• At low fluences, over 80% of charges survived after 1 nanosecond, with recombination occurring on a 200 picosecond timescale.

Conclusions:

• PBDTTPD:PCBM blends exhibit rapid charge carrier generation and separation.
• Minimizing annihilation processes is essential for maximizing charge carrier yield in OSCs.
• Efficient charge carrier survival in PBDTTPD:PCBM blends suggests high potential for organic solar cell applications.