316045.fig.001
Figure 1: Molecular structures of poly(3-hexylthiophene) (P3HT), poly(9,9′-dioctylfluorene-co-bithiophene) (F8T2), -phenyl C61-butyric acid methyl ester (PCBM), and -phenyl C71-butyric acid methyl ester (PC70BM).