Ternary Active Layers for Neutral Color Semitransparent Organic Solar Cells with PCEs over 4%

Ternary blend active layers that include an additional electron donor or electron acceptor material provide the means to easily tune the transmission properties of semitransparent organic solar cells (OSCs) by simply changing the relative concentration of each active material. We added a nonfullerene acceptor (ITIC) into a well-studied donor:acceptor active layer (PCDTBT:PC71BM) that can be produced in air and demonstrates long-term operational stability. We investigated the optoelectronic properties of the resulting OSCs and observed that partially replacing the fullerene electron acceptor, PC71BM, with ITIC produces uniformly absorbing active layers, which, however, generate a slight decrease in photovoltaic performances compared to the reference binary OSCs. On the other hand, adding ITIC to an optimized PCDTBT:PC71BM ratio of 1:4 leads to a slight increase in short-circuit current density from these ternary OSCs with respect to the binary ones. In semitransparent OSCs fabricated with a PCDTBT:PC71BM:ITIC ratio of 1:4:1, power conversion efficiencies of 4%, average visible transparencies around 40% and color rendering indices of 97 are produced. As the addition of ITIC does not affect the long-term operational stability of the unencapsulated PCDTBT:PC71BM OSCs, our study opens the path to the fabrication of stable semitransparent OSCs with balanced optoelectronic properties that could readily be applied as solar energy-harvesting photovoltaic windows.