New phenothiazine dyes containing benzothiadiazole-acceptor for dye-sensitized solar cells

In this work, we designed and synthesized two new phenothiazine dyes CBPTZ-BTD1 and CBPTZ-BTD2, which employed the electron-accepting moiety of benzothiadiazole (BTD). The structural difference between the two new dyes is due to the presence of an ethynyl unit between BTD and the benzoic acid. With respect to its congener CBPTZ-BTD1, CBPTZ-BTD2 with the insertion of ethynyl group shows a more coplanar molecular skeleton, which endows CBPTZ-BTD2 with a higher dye loading and a strengthened ICT effect, resulting in a red-shifted ICT absorption with a higher molar extinction coefficient. Besides, CBPTZ-BTD2 has a longer electron lifetime in comparation with CBPTZ-BTD1 without the linear ethynyl unit, as reveled by OCVD and EIS measurements. Therefore, CBPTZ-BTD2 exhibits a better photovoltaic performance with an enhanced JSC of 14.04 mA cm−2 and VOC of 0.82 V, leading to an improved PCE of 7.33 %.