Multi-junction polymer solar cells

Efficiency of organic solar cells is limited by their poor match to the solar spectrum, particularly in the near-infrared region. The development of devices which can absorb light of lower energy than the active polymer layer could result in dramatic improvement in polymer solar cells efficiencies. Towards this end, near-infrared dyes were investigated for use as components in multi-junction polymer solar cells. Dyes with appropriately positioned energy levels to promote exciton dissociation and charge transport were selected, and their electronic properties were probed using cyclic voltammetry. Specifically, zinc phthalocyanine (ZnPc) and Aluminum 1, 8, 15, 22-tetrakis(phenylthio)-29H,31H-phthalocyanine chloride (AlPc) were chosen. Single junction devices were fabricated using each of these different candidates. The donor:acceptor ratio was found to be of critical importance for improved efficiency. The simultaneous use of both dyes was found to be possible due to adequate energy alignment which further increases the performance of the devices, in particular by increasing the open circuit voltage.