Synthesis and Characterization of an Alkoxythiazole-thiazolothiazole Semiconducting Polymer for Organic Solar Cells

Abstract

We report the synthesis and characterization of a new thiazolothiazole (TzTz)-based semiconducting polymer incorporating the alkoxythiazole unit in the polymer backbone (PTzTTz-BOoHD). The introduction of the alkoxythiazole unit in a thiophene–TzTz polymer (PTzBT-BOHD) lowered the LUMO energy level while keeping the HOMO energy level, resulting in a narrower bandgap. The solar cell with PTzTTz-BOoHD showed photoresponse in a wider spectral range (∼740 nm) compared to that with PTzBT-BOHD and with a thiophene–TzTz polymer having the alkoxy thiophene unit (PTzBT-BOoHD). Although the fill factor (FF) of the cell based on PTzTTz-BOoHD was lower than the cell based on PTzBT-BOHD and -BOoHD, the maximum PCE of the cell based on PTzTTz-BOoHD resulted in 6.2%, which was comparable to and higher than the cell based on PTzBT-BOHD and -BOoHD, respectively. While PTzTTz-BOoHD showed good crystallinity in the polymer film, it was reduced in the film blended with PC₆₁BM, which is likely an origin of the drop of FF. As PTzTTz-BOoHD has more suitable electronic structures for solar cells such as a deep HOMO level and a narrow bandgap, compared to the other two polymers, we expect that PTzTTz-BOoHD would demonstrate higher PCE by further device optimization.