The tandem concept is especially attractive for organic photovoltaics (OPV) owing to its potential to significantly improve the power conversion efficiency (PCE) of OPV single cells by ~40%.1 The performance of organic tandem solar cells is directly determined by the functionality and reliability of intermediate (interconnection) layer as well as the photovoltaic properties of spectrally-matched sub-cells. The intermediate layer on the one hand is responsible for selectively collecting charge carriers from sub-cells, and on the other hand has to facilitate efficient charge recombination at its inner interface. Although many OPV systems have been developed to obtain remarkable PCE of 10-12%, only very few candidates have been investigated and characterized in the tandem configurations. Furthermore, the required information for large-scale mass production was barely explored, such as roll-to-roll compatibility, environmental resistivity, device operational stability, etc.
In this contribution, we will demonstrate interface and architecture design rules for solution-processed organic tandem solar cells towards large-scale production. A solution-processed hybrid hole-transporting layer consisting of MoOx nanoparticles and PEDOT:PSS is engineered to be fully compatible with state-of-the-art OPV systems, and can be further applied in combination with ZnO for high-performance organic tandem solar cells.2 Moreover, a series of high-performance polymer donors, such as PTB7-Th (PCE10) and PffBT4T-2OD (PCE11) are investigated and analysed to assess their applicability for large-scale mass production.3,4 Organic tandem solar cells with all the semiconducting layers printed in air at fairly low temperatures achieve a high PCE over 10% along with an unprecedented high fill factor >76%.
 N. Li et al., Adv. Energy Mater. 2014, 4, 1400084.  X. Du et al., Adv. Energy Mater. 2017, 7, 1601959.  N. Li et al., Energy Environ. Sci. 2015, 8, 2902.  N. Li et al., Nat. Commun. 2017, 8, 14541.