Ester-Substituted Pentathiophene Copolymer-Based Sky-Blue Semitransparent Solar Cells for Building Windows

For oligothiophene-based donor polymers, the reports of pentathiophene are rare, while other oligothiophenes (bi-, ter-, and quaterthiophene) have been broadly studied. Here, we synthesized one wide-band-gap (1.88 eV) polymer PFTzTT-3TC, based on ester-substituted pentathiophene and benzotriazole. PFTzTT-3TC:ITIC (1.0:1.0)-based polymer photovoltaic cells exhibited the best PCE of 8.21% and Voc of 0.90 V without an additive (such as DIO, 1-CN) or post-treatment. These are the highest PCE and Voc for ester-substituted pentathiophene-based devices to date. Furthermore, semitransparent polymer photovoltaic cells with an active blend of PFTzTT-3TC:ITIC (1.0:1.0) demonstrate a similar Voc of 0.89 V and a PCE of 6.43% with an AVT of 26.77% and an AT of 30.58% and CIE (0.25, 0.21). The sky-blue of semitransparent devices is useful for photosynthesis in plants and visual comfort for humans and makes this material suitable for building windows.