Effects of Ratio of Electron Donor/Acceptor Moieties on Photophysical, Electronic and Photovoltaic Properties of Donor-π-Acceptor Functionalized Materials

Three conjugated donor-pi-acceptor materials have been synthesized by different ratios of donor-acceptor moieties in molecules, which fabricated with asymmetrical and symmetrical structures. UV-vis absorption data show that increasing of the number of electron-withdrawing moieties in molecule leads to red shift behaviors on the pi-pi* peaks and the intramolecular charge transfer peaks. Cyclic voltammetry curves show that all compounds present a reversible first oxidation process whose potential change with the number of electron-withdrawing moieties increasing. The single-layer bulk heterojunction solar cells have been fabricated with the materials as donors and PCBM as acceptor. The increasing of the number of electron-withdrawing moieties in the donor materials induces an extension of the photoresponse in the visible spectral region, an increase of the open-circuit voltage and a large enhancement of the external quantum efficiency of devices. Finally, the solvation-induced morphology effects on performances of devices have been investigated by using aromatic and nonaromatic solvents.