Pure and Applied Chemistry

Abstract: Polymer solar cells have shown high potential to convert solar energy into electricity in a cost-effective way. One of the basic reasons limiting the polymer solar cell efficiency is insufficient absorption of the solar radiation by the active layer that limits the photocurrent. To increase the photocurrent, one needs low-bandgap materials with strong absorption below 2 eV. In this work, we study two types of low-bandgap materials: ground-state charge-transfer complexes (CTCs) of a conjugated polymer, MEH-PPV (poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene]), and an exohedral metallocomplex of fullerene, (η²-C₆₀)IrH(CO)[(+)DIOP] (IrC₆₀). We demonstrate that the CTC formed between MEH-PPV and conjugated molecules with high electron affinity, namely, 2,4,7-trinitrofluorenone (TNF) and 1,5-dinitroantraquinone (DNAQ), can have strong optical absorption extending down to the near infrared. We have observed that the photoexcited CTC can generate free charges. We also report on optical studies of IrC₆₀ as a possible acceptor for polymer/fullerene solar cells. IrC₆₀ strongly absorbs in the visible spectral range, in particular in the red part, and therefore has a potential for increasing the photocurrent as compared with polymer/methanofullerene solar cells. Our studies of MEH-PPV/IrC₆₀ blended films show that long-lived charges are efficiently generated at MEH-PPV upon photoexcitation of the blend.