Incorporation of Hydrogen Molybdenum Bronze in Solution-Processed Interconnecting Layer for Efficient Nonfullerene Tandem Organic Solar Cells

Tandem solar cells are attractive because they can break the Shockley–Queisser efficiency limit of single-junction cells. However, it is still quite challenging to fabricate efficient nonfullerene tandem organic solar cells (OSCs) because of their complicated and vulnerable multilayers and interfaces. The interconnecting layer (ICL) between two subcells is the key part in efficient tandem solar cells, which should be designed properly based on the property of active layers. Herein, the incorporation of hydrogen molybdenum bronze (H x MoO 3 ) between the bottom active layer and PEDOT:PSS/ZnO to form a new ICL is proposed. The contribution of the H x MoO 3 is two fold: 1) it can well wet the hydrophobic active layer surface and form a uniform film. It provides a hydrophilic surface for the following deposition of PEDOT:PSS; 2) the H x MoO 3 has a high work function of 5.4 eV that is higher than PEDOT:PSS (5.0 eV) and can extract holes more efficiently from the active layer with the deep highest occupied molecular orbital energy level. Nonfullerene tandem solar cells with a high fill factor of 76.0% and power conversion efficiency of 15.03% are obtained with this ICL.