Femtosecond transient studies of photoinduced charge transfer in~polymers doped with strong acceptor molecules; applications~for organic solar cells

Current developments in organic solar cells ($\sim $5{\%} efficiency nowadays)~require understanding and control of photoinduced charge carrier transfer and electronic state dynamics of donor-acceptor pairs. One current drawback to organic solar cell efficiency is negligible absorption in the near infrared region of the solar spectrum. We provide and compare evidence that poly(2-methoxy-5(2'-ethyl)hexoxy-phenylenevinylene) (MEH-PPV) and regio-regular poly-3-hexyl thiophene (RR-P3HT) doped with 2,7-dinitrofluorenone (DNF) or 2,4,7-trinitrofluorenone (TNF) form below-gap charge transfer complex state that can extend absorption into the near infrared. Using fs transient and CW spectroscopies we found that the photoluminescence and~mid-ir photoinduced absorption (PA)~band of excitons~are simultaneously quenched, when excited in the visible/uv or near ir. We compare our results to those of comparable systems using C$_{60}$ as acceptor molecules.