Towards optimization of P3HT:bisPCBM composites for highly efficient polymer solar cells

The optimization of the polymer solar cells based on regioregular poly(3-hexylthiophene) (P3HT) and the bisadduct of phenyl C61-butyric acid methyl ester (bisPCBM) is studied thoroughly as a role of solvent-annealing effect as well as different concentration of bisPCBM. In the case of P3HT:bisPCBM of 1 : 0.8 w/w, more balanced electron and hole mobilities are observed, resulting in better performance of the solar cells. Under the best balance conditions such as P3HT:bisPCBM of 1 : 0.8 w/w, the solvent annealing is employed to further clarify the optimization of the devices. Such a treatment leads to the formation of crystalline P3HT domains in the blend films, which is determined by X-ray diffraction, UV-vis spectroscopy, and atomic force microscopy. From our experiment, one can conclude that the best power conversion efficiency of 3.75% is achieved in a layered structure of P3HT:bisPCBM of 1 : 0.8 w/w for a solvent-annealing time of 24 h.