Donor and Acceptor Behavior in a Polyfluorene for Photovoltaics

The authors study photovoltaic devices based on a red-absorbing conjugated polymer poly(2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4\u27,7\u27-di-2-thienyl-2\u27,1\u27,3\u27-benzothiadiazole)) (APFO-3). The polymer acts as an electron donor when blended with ZnO nanoparticles, giving a short-circuit quantum efficiency of 28%. When blended with poly(3-hexylthiophene) (P3HT), however, the APFO-3 acts as an electron acceptor, giving a short-circuit quantum efficiency of 12%. The authors study this charge-transfer process by comparing photoinduced absorption spectra of the hybrid blends with the absorption spectra of chem. doped APFO-3, which allows one to distinguish features due to pos. and neg. polarons. The authors also present dark current measurements of single-carrier devices which demonstrate that APFO-3 has similar mobilities for electrons and holes, consistent with ambipolar behavior in photovoltaic devices. [on SciFinder (R)