Synthesis, Properties, and Solar Cell Performance of Poly(4-(p-alkoxystyryl)thiazole)s

A series of polythiazoles (PvTzs) featuring conjugated styryl sidechains equipped with different solubilizing p-alkoxy-groups (OR, R = n-octyl, n-dodecyl, 2-ethylhexyl, 2-hexyldecyl) is prepared by Negishi-coupling polycondensation. Soluble material with number-average molecular weights of up to M-n = 8.5 kDa (polydispersity (PDI) = 1.3, degree of polymerization (DPn) approximate to 20) is obtained, with a head-to-tail content of the PvTzs of approximate to 77%, as estimated from comparison with reference polymers. The polymers exhibit optical absorption properties similar to their polythiophene analogues, while their electrochemical characterization shows a significant stabilization of their frontier orbital levels. Fluorescence measurements indicate that upon excitation of the electron rich alkoxystyryl side-chains charge transfer onto the more electron deficient polythiazole backbone occurs. This finding is corroborated by density functional theory (DFT) calculations on oligomeric model systems, which also consistently reproduce the optical properties observed for the polymers. The potentialities of these materials for applications in organic electronics can be demonstrated by their use as donor materials in organic photovoltaic cells, which exhibit higher open circuit voltages (V-OC, up to 0.86 V) than P3HT- or analogous polythiophene-based cells (V-OC = 0.5-0.6 V).