Effect of dual annealing upon photovoltaic properties of polymer solar cells based on poly (3-hexylthiophene)

A dual annealing method comprised of toluene vapor treatment and post thermal annealing was employed to fabricate polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and -phenyl-C₆₁-butyric acid methyl ester (PCBM) film. It is found that the P3HT crystallinity and chain ordering can be dramatically enhanced by this annealing process as compared with the films treated merely with solvent vapor annealing, which is verified by a higher X-ray diffraction intensity peak and clearly visible fibrillar crystalline domains of P3HT. The result suggests that a favorable equilibrium condition was established by dual annealing in the morphology reorganization. Due to the morphological improvement of active layer, the dually annealed PSCs show better overall performances, with a mean power conversion efficiency of 4.06% and an increase in each electrical parameter, than any solely annealed ones.