Efficient light harvesting in multiple-device stacked structure for polymer solar cells

We demonstrate a multiple-device stacked structure of polymer solar cells for efficient light harvesting. Two polymer photovoltaic cells are stacked together and connected in series or in parallel to achieve a tandem structure. In this two-cell structure, a multilayer semitransparent electrode, made of lithium fluoride (LiF)/aluminum (Al)/gold (Au), is used as the top contact in the bottom cell to efficiently transmit the unabsorbed photons to the upper cell. Maximum transparency of up to 80% is achieved for the semitransparent cathode. Upon stacking, the open-circuit voltage and the short-circuit current are almost doubled compared to a single cell.