High Molecular Weights, Polydispersities, and Annealing Temperatures in the Optimization of Bulk-Heterojunction Photovoltaic Cells Based on Poly(3-hexylthiophene) or Poly(3-butylthiophene)


  • The authors thank Prof. Jack Cousseau, Prof. Piétrick Hudhomme, and Prof. Jean-Michel Nunzi, (Université d'Angers), Dr. Stéphane Guillerez and Dr. Gil Vilaça (CEA Grenoble), all other members of the CSPVP consortium, and Farid Ouhib, Dr. Jeanne François, and Dr. Pierre Iratçabal (Université de Pau) for their enlightening discussions and warm encouragement. Gérald Clisson and Francis Ehrenfeld are gratefully thanked for technical assistance. Sincere thanks are also extended to the CNRS and the ADEME through the ‘Cellules Solaires Photovoltaïques Plastiques' (CSPVP) research program, under program 0105148, contract number 9905019, for funding R.C.H.


A series of poly(3-hexylthiophene)s (P3HTs) and poly(3-butylthiophene)s (P3BTs) with predetermined molecular weights and varying polydispersities are prepared using a simplified Grignard metathesis chain-growth polymerization. Techniques were elaborated to prepare extremely high molecular weight P3HT (number-average molecular weight of around 280 000 g mol–1) with a low polydispersity (< 1.1) without resorting to fractionation. Optimization of the annealing of a series of solar cells based on blends of poly(3-alkylthiophene)s (P3ATs) and [6,6]-phenyl C61 butyric acid methyl ester indicates that the polydispersities, molecular weights, and degrees of conjugation of the P3ATs all have an important impact not only on cell characteristics but also on the most effective annealing temperature required. The results indicate that each cell requires annealing treatments specific to the type of polymer and its molecular weight distribution.