title: Intensity Dependent Femtosecond Dynamics in a PBDTTPD-Based Solar Cell Material.
abstract: PBDTTPD is a conjugated polymer with high power conversion efficiency if used in organic solar cells together with fullerene derivatives. We have investigated for the first time the excited state dynamics of pristine PBDTTPD thin film as well as the ultrafast evolution of charge carriers in PBDTTPD:PCBM bulk heterojunction blend using femtosecond transient absorption spectroscopy. In the latter, charges appear within the time resolution of the experiment (<100 fs), but clean spectral signatures allowed to directly follow slower ∼1 ps charge separation. Only the slower quenching component competes with exciton-exciton and exciton-charge annihilation, leading to a reduced yield of charge carriers at high laser fluence. Our excellent measuring sensitivity made it possible to reduce pump power to a point where annihilation is quasi suppressed. In this case >80% of charges survive after 1 ns; the rest recombines (most probably geminately) on the 200 ps time scale.
authors: Arun Aby
authors: AA
authors: Paraecattil
authors: ‡Department of Chemistry, Université Laval, G1K 7P4 Quebec City, Quebec, Canada.
authors: Serge
authors: S
authors: Beaupré
authors: ‡Department of Chemistry, Université Laval, G1K 7P4 Quebec City, Quebec, Canada.
authors: Mario
authors: M
authors: Leclerc
authors: Jacques-E
authors: JE
authors: Moser
authors: Natalie
authors: N
authors: Banerji
keywords: PCBM; bulk heterojunction; charge carriers; conjugated polymer; excitation power; excited state; fullerene blend; laser fluence; organic photovoltaics; thin film; transient absorption spectroscopy; ultrafast