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

Current developments in organic solar cells ($\sim $5{\%} efficiency nowadays)~require understanding and control of 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 evidence that poly(2-methoxy-5(2'-ethyl)hexoxy-phenylenevinylene) (MEH-PPV) doped with 2,7-dinitrofluoronone (DNF) forms a charge transfer complex state that can extend absorption into the near infrared. We found that photoluminescence and the~photoinduced absorption (PA)~band of excitons~are simultaneously quenched. Ultrafast spectroscopic measurements with spectral range from 0.2 to 1.2 eV provide insights into polaron and exciton band dynamics~for these complexes. We also suggest a mechanism for bimolecular charge transfer in this system.