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 PC 61 BM, 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.