Synthesis of metal-free organic dyes containing tris(dodecyloxy)phenyl and dithienothiophenyl units and a study of their mesomorphic and photovoltaic properties

In this study we synthesized three metal-free organic dyes (Cpd11, Cpd16, and Cpd22) featuring 3,4,5-tris(dodecyloxy)phenyl and cyanoacrylic acid moieties as electron-donor and electron-acceptor/anchoring units, respectively, linked through various dithienothiophenyl conjugated spacers. Cpd16 exhibits mesomorphic properties, confirmed through polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction (XRD), due to the appropriate ratio of the lengths of its flexible chain to its rigid core. Molecular modeling of Cpd16, and its d-spacing determined from XRD data, verified the existence of a tilt angle in the SmC phase. Among these metal-free organic dyes, a dye-sensitized solar cell incorporating Cpd16 exhibited the best performance, presumably because of its better packing and its mesomorphic properties; the power conversion efficiency was 3.72% (Voc=0.58 V; Jsc=9.98 mA cm−2; FF=0.65) under simulated AM 1.5 irradiation (100 mW cm−2).