Direct observation of sub-100 fs mobile charge generation in a polymer-fullerene film

The formation of mobile charges in a roll-to-roll processed poly-3-hexylthiophene-fullerene bulk heterojunction film is observed directly by using transient terahertz spectroscopy with sub-100?fs temporal resolution. The transient terahertz ac conductivity reveals that 20% of the incident pump photons are converted into highly delocalized charges within the 40?fs, 3.1?eV pump pulse duration, which then rapidly becomes localized within 120?fs. Approximately 2/3 of these carriers subsequently decay, possibly into an exciton, on a 1?ps time scale.