SL 11

SYNTHESIS AND CHARACTERISATION OF REGIOREGULAR POLYTHIOPHENES SUBSTITUTED BY AROMATIC GROUPS FOR BULK HETEROJUNCTION PHOTOVOLTAIC CELLS

F. Ouhib^a, R.C. Hiorns^a, R. de Bettignies^b, S. Bailly^b, A. Khoukh^a, J. Desbrières^a, Ch. Dagron-Lartigau^a

^aIPREM EPCP,CNRS-UMR 5254, Université de Pau et des Pays de l'Adour, Hélioparc 2 Av P. Angot, 64053 Pau Cedex France

^bCEA-Saclay, LCS, DRT-LITEN-GENEC, Bât. 451, 91191 Gif-sur-Yvette France

Polythiophene derivatives for photovoltaic devices

A series of regioregular poly[3-(4-octylphenyl)thiophene]s (POPT) were prepared using two methods of polymerisation. Initially, 3-(4-octylphenyl)thiophene was polymerised using the oxidative route with FeCl₃ and yielded highly regioregular polymers with polydispersities greater than 2. The use of the Grignard metathesis chain-growth polymerisation (GRIM method) performed in diphenyl ether instead of tetrahydrofuran permitted the preparation of high molecular weight POPTs with low polydispersities and high regioregularities (evaluated using using ¹H NMR). The thermal and optical properties of the samples obtained from the GRIM method with different molecular weights were studied. Thin films of POPTs exhibited high values of lmax (around 600 nm) and an optical band gap of 1.75 eV indicating high conjugation lengths. These POPTs were used as an active thin layer in organic solar cells in combination with the acceptor [6,6]-phenyl C61 butyric acid methyl ester (PCBM). The results will be presented, comparing the oxidative and the GRIM methods, and discussing the effect of molecular weights. As an extension of this work, alternated and diblock copolymers combining tolylthiophene and hexylthiophene were prepared using both methods. The optical and photovoltaic characteristics will be presented and compared to POPTs and P3HTs.