Molecular Design Strategy toward Robust Organic Dyes in Thin-Film Photoanodes

The photo-, thermal, and water stability of dyes is indispensable for the commercialization of dye-sensitized solar cells, necessitating the development of systematic molecular design strategies to enhance the stability of the dyes. Therefore, we prepared dithieno[3,2-b:2′,3′-d]thiophene (DTT)-based dyes, by varying the functional group on the donor moiety (TP-1, H-; TP-2, methoxy-; TP-3, carbazolyl-; and TP-4, 2-ethylhexyloxy-). Among these dyes, TP-4 exhibits the highest power conversion efficiency of 8.86% (Jsc = 15.9 mA cm–2, Voc = 0.76 V, FF = 0.73) with iodine electrolyte on a thin TiO2 active layer (3.5 μm), as well as strong resistance to photo-, thermal, and water stresses. UV–vis spectroscopy, intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltaic spectroscopy were used to analyze the dyes. On the basis of these analyses, we suggest a molecular design strategy for simultaneously enhancing the stability of photo-, thermal, and water stresses.