Sophie Roquet

Three-dimensional tetra(oligothienyl)silanes as donor material for organic solar cells

Tetrahedral conjugated systems involving four conjugated oligothiophene chains fixed onto a central silicon node (1, 2) have been synthesized and used as donor materials in hetero-junction solar cells. Bilayer solar cells have been realized by thermal evaporation of compounds 1 and 2 as donors and N,N′-bis-tridecylperylenedicarboxyimide as an acceptor. Comparison of the performances of these devices to those of a reference system based on dihexylterthienyl (H3T) shows that despite comparable effective conjugation lengths, the 3D compounds 1 and 2 lead to a power conversion efficiency four–five times higher, suggesting better absorption of the incident light and better hole transport properties. Whereas fabrication of bulk hetero-junction with H3T was prevented by the lack of film forming properties, a prototype bulk hetero-junction based on compound 2 as the donor and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor has been realized. A short-circuit current density of 1.13 mA cm−2 and a power conversion efficiency of 0.30% has been measured under AM 1.5 simulated solar irradiation at 80 mW cm−2.

3,4-Phenylenedioxythiophene (PheDOT): a novel platform for the synthesis of planar substituted π–donor conjugated systems

3,4-Phenylenedioxythiophene (PheDOT), a benzenic analogue of 3,4-ethylenedioxythiophene (EDOT), has been synthesized using two different routes namely etherification of 2,5-dicarboethoxy-3,4-dihydroxythiophene with halo-aromatics and transetherification of 3,4-dimethoxythiophene with catechols. Quantum calculations and electrochemical measurements show that replacement of the ethylene bridge of EDOT by a phenyl group leads to an increase of the HOMO level and to a stabilization of the cation radical, making electropolymerization of PheDOT more difficult than that of EDOT. The synthesis of several PheDOT derivatives is described together with preliminary results on their electrochemical polymerization and on the properties of the resulting polymers and copolymers.

3D-conjugated systems based on oligothiophenes and phosphorus nodes

3D-conjugated systems based on oligothiophene segments grafted on a phosphorus or on a phosphine oxide node have been synthesized. Under Stille coupling conditions, bromide terminated thienyl phosphine derivatives undergo a breaking of the phosphorus-carbon bond attributed to a ligand exchange with the Pd catalyst. The electronic properties of the new compounds have been analyzed by UV-vis and fluorescence spectroscopy and cyclic voltammetry.