Characterization of tandem organic solar cells

To the Editor — The tandem solar cell approach is a promising concept for organic photovoltaics (OPVs). However, efficiency determination or, in general, electrical characterization of multi-junction solar cells is challenging. We performed a literature survey of publications reporting tandem OPV characterizations over the period January 2009 to September 2014 and came to the alarming conclusion that 96% of the published efficiencies were not measured according to the relevant standards.