Influence of Molecular Weight Distribution on the Gelation of P3HT and its Impact on the Photovoltaic Performance

P3HT is a semirigid and semicrystalline polymer with a strong tendency to postcrystallize in solid films upon thermal annealing. Recent investigations showed that macroscopic, crystalline P3HT fibers can already be precipitated from solution, depending on the combination of solvent systems used. In this paper we investigate the mechanism and the dynamics of gelation in P3HT solutions. Rheological and absorption measurements in solution reveal a distinct two-step mechanism. In a first step, aggregates are formed which, in a second step, link to each other into a thermoreversible gel. The correlation between the gelation dynamics and the molecular weight distribution is discussed in more detail for a nonhazardous, printing friendly solvent system.