Reduced optical loss in mechanically stacked multi-junction organic solar cells exhibiting complementary absorptions

This paper describes a promising approach toward preparing effective electrical and optical interconnections for tandem organic photovoltaic devices (OPVs). The first subcell featured a semi-transparent electrode, which allowed a portion of the solar irradiation to pass through and to enter the second subcell exhibiting complementary absorption behavior. The resulting multi-junction OPV had multiple contacts such that the subcells could be easily connected either in series or in parallel. More importantly, we used UV-curable epoxy to "mechanically" stack the two subcells and to eliminate the air gap between them, thereby reducing the optical loss induced by mismatches of refractive indices. Therefore, an improved power conversion efficiency of approximately 6.5% has been achieved.