Influence of alkyl substitution pattern in thiophene copolymers on composite fullerene solar cell performance

Two thiophene-alkylthiophene copolymers with identical molecular weight, composition, and electronic structure have been examined to assess the influence of their high degree of crystallinity on the composite fullerene solar cell performance. These polymers, poly(3,3-didodecylquaterthiophene) (PQT-DD) and poly(3-dodecylthiophene-co-thiophene) (P3DDT-co-T), are structurally equivalent except for the sequence distribution of substituted and unsubstituted thiophene rings and both are soluble in chloroform, chlorobenzene, and dichlorobenzene. It was observed that the polymer with random primary structure was superior to the polymer with the precisely defined primary structure, in the context of solar cell performance. It was observed that P3DDT-co-T's superior ability for the formation of bicontinuous structure, brought about by the decreased tendency for crystallization contributed to the significant increase in solar efficiency.