A simple merocyanine tandem solar cell with extraordinarily high open-circuit voltage

We present a highly efficient tandem solar cell based on a merocyanine dye, containing two identical subcells connected in series. A recombination layer of Al/MoO(3) was used. Due to a substantial improvement of the fill factor, the overall efficiency of the tandem cell was even higher than that of the single-cell reference with identical active layer thickness. By combining the planar heterojunction and the bulk heterojunction concept, efficiencies up to 4.8% were achieved while maintaining a rather simple, fully vacuum-processed device stack consisting of only four organic layers. The optimized open-circuit voltage was as large as 2.1V. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3657145]