Recent progress of interconnecting layer for tandem organic solar cells

This paper has reviewed： （1） the two unique advantages of tandem organic solar cells （OSCs） compared to single OSCs; （2） the challengings as well as strategies to develop qualified interconnecting layer （ICL） for tandem OSCs. More specifically, firstly, the two key advantages unique to tandem OSCs as compared to single OSCs, namely minimizing sub-bandgap transmission and thermalization loss as well as realizing optical thick and electrical thin structures, have been discussed. Secondly, the ICL, as one of the most challenging issue in tandem OSCs that needs to fulfill the optical, electrical and mechanical requirements simultaneously to realize a qualified ICL has been reviewed. As one of the most challenging requirement among the three, the electrical requirement and its corresponding three different solving strategies have been discussed in detail, revealing a bright future for developing a general strategy to realizing qualified ICL composed of different hole transporting layer （HTL） and electron transporting layer （ETL）.