The optical absorption in organic solar cells, and hence theirefficiency to convert sunlight into electricity, is limitedby both a confined spectral absorption range and the very thin active layers which are required since polymers have short charge carrier diffusionlengths. We propose to make the most of thisapparent 'drawback' by using transparent contacts on both sides ofthe diode, leading to brilliant red-coloured semitransparent solarcells. Such cells are interesting for new, aesthetically appealingapplications where coloured glasses or foils with the additionalbenefit of providing electric power are desired. Maybe even moreimportantly – such semitransparent solar cells are essential formechanically stacked tandem arrays where two subcells arecombined. We investigated different cathodes based on Al-doped ZnO and thin LiF and Al layers. Apparently, the different cathode layer preparation conditions strongly influence the cellperformance. Our standard LiF/Al cells donot usually require annealing for improved efficiencies, incontrast to cells with sputtered cathodes. For the latter, athermal post-treatment can greatly enhance the performance,depending on the sputtering process. We could demonstrate power conversion efficiencies of up to 3.4% for single cells and up to 4.2% for stacked tandem arrays.