(E)-2,2'dibromo-7,7'-bis(diphenylamino)-9,9' bifluorenylidene as a new electron acceptor for organic photovoltaic cells.

(E)-2,2'-Dibromo-7,7'-bis(diphenylamino)-9,9'-bifluorenylidene (BDPABF) was synthesized as a new non-fullerene-type electron acceptor for organic photovoltaic cells. The UV-visible absorption spectra of BDPABF showed two main bands at 319 and 474 nm in a chloroform solution and 320 and 481 nm as a solid thin film. The optical band gap of BDPABF was determined to be 2.34 eV by measuring the onset absorption wavelength of the solid thin film. The ionization potential of BDPABF was determined to be 5.59 eV using photoelectron spectroscopy. The measured lowest unoccupied molecular orbital energy level of BDPABF was - 3.25 eV. Its electron-accepting ability was investigated through a Stern-Volmer quenching experiment. The intensity of the photoluminescence of P3HT dramatically decreased upon the addition of BDPABF. The measured Stern-Volmer quenching constant was 5.3 x 10(4) M(-1). Photovoltaic devices were fabricated using P3HT as the electron donor and BDPABF as the electron acceptor at various composition ratios. The optimized device showed a maximum power conversion efficiency of 0.27% with an open-circuit voltage of 0.71 V, short-circuit current density of 1.29 mA/cm2, and fill factor of 0.29 after thermal annealing at 100 degrees C for 5 min.