• charge recombination;
  • conjugated polymer;
  • fullerene;
  • open-circuit voltage;
  • organic solar cell
Thumbnail image of graphical abstract

The molecular mechanism underlying open-circuit voltage (VOC) is studied by analyzing current–voltage characteristics of solar cells on the basis of the equivalent circuit model. As reported by H. Ohkita and co-workers on page 229, VOC is found to depend not only on the HOMO–LUMO energy gap but also on the electronic couplings of the cell components. This suggests that recombination in the blends studied is not a diffusion-limited reaction. On the basis of these findings, a molecular design is proposed to achieve an improved VOC effectively without loss of the charge-generation efficiency.