Single-material organic solar cells with conjugated electron-donor alkoxy-substituted bithiophene units and electron-acceptor benzothiadiazole moieties alternating in the main chain

Main chain conjugated linear polymers, constituted by alternating electron-donor(D) and -acceptor (A) moieties, have been prepared with the aim of testing their performances asphotoactive components in single material organic solar cells (SMOSCs). The D moiety isconstituted by bithiophene co-units bearing in the position 3 of the thiophene ring an hexyloxy, ahexyloxymethyl or a hexyl group, while the A moiety is represented by the benzothiadiazolegroup. The D-A polymers were obtained in high yield through the poorly demanding oxidativeFeCl3 polymerization process - starting, respectively, from the related precursors 4,7-bis(3-hexyloxythiophen-2-yl)benzo[c][2,1,3]thiadiazole, 4,7-bis[3-(6-methoxyhexyl)thiophen-2-yl]benzo[c][2,1,3]thiadiazole and 4,7-bis(3-hexylthiophen-2-yl)benzo[c][2,1,3]thiadiazole - withlow dispersity indexes, close to the monodisperse state, after fractionation with methanol. Thematerials have been thoroughly characterized for their physical and structural properties and thentested for photoconversion efficiency in SMOSCs by using different deposition procedures of thephotoactive component. In agreement with Kelvin probe force microscopy (KPFM)measurements, the best photovoltaic performance was observed for the polymer based onconjugated 3-alkoxythiophene and benzothiadiazole moieties, achieving significantphotocurrents for this type of fully conjugated alternating D-A structures (Jsc = 2.63-3.72 mAcm-2).