Editorial for the special issue dedicated to tandem solar cells based on organic and polymer materials

Organic photovoltaics (OPV) have been tremendously successful at the academic level as evidenced by an enormous body of scientific reports. The power conversion efficiency for OPV has as a consequence of the intense research effort experienced a corresponding growth and today single junction OPV reportedly present record power conversion efficiencies of around 10% for tiny active areas. The scaled power conversion efficiency however still remains significantly lower. In an effort to improve both record and scaled power conversion efficiencies several schemes have been pursued and one of the most promising is the well-known tandem concept where one or more junctions are stacked on top of each other. In the context of OPV this presents a significant processing challenge which is the subject of this issue where a selection of papers have been collected that cover very broadly from roll processing of multi-junctions through tandem modules, interlayer design and life cycle analysis. All-in-all an excellent collection of papers for the student as well as the researcher working on and developing OPV. I wish you a good few hours of reading.