title: Simple and versatile molecular donors for organic photovoltaics prepared by metal-free synthesis.
abstract: Donor-acceptor molecules (D-π-A) built by connecting a diphenylhydrazone block to a dicyanovinyl acceptor group via various thiophene-based π-conjugating spacers (1-5) were synthesized from mono- or dialdehydes by a simple metal-free procedure. Cyclic voltammetry and UV/Vis absorption spectroscopy show that the extension and/or increase of the donor strength of the spacer produces a decrease of the HOMO and LUMO energy level, a red shift of the absorption spectrum and an increase of the molecular absorption coefficient. Compared to solutions, the optical spectra of spin-cast thin films of compounds 1-3 show a broadening and red shift of the absorption bands, consistent with the formation of J-aggregates. In contrast the blue shift observed for the EDOT-containing compounds 4 and 5 suggests the presence of H-aggregates. Solution-cast and vacuum-deposited films of donors 1-5 were evaluated in solar cells with fullerene C60 as acceptor. A power-conversion efficiency among the highest reported for bilayer devices of basic configuration was obtained with compound 2. On the other hand, the results obtained with 4 and 5 suggest that the presence of EDOT in the structure can have deleterious effects on the organization and performances of the donor material.
authors.affiliation: Group Linear Conjugated Systems, CNRS Moltech-Anjou, University of Angers, 2 Boulevard Lavoisier 49045 Angers (France); Babes Bolyai University, Center of Supramolecular Organic and Organometallic Chemistry (CSOOMC), Cluj-Napoca, 11 Arany Janos Street, 400028 Cluj-Napoca (Romania).
authors.forename: Andreea
authors.initials: A
authors.lastname: Diac
authors.forename: Dora
authors.initials: D
authors.lastname: Demeter
authors.forename: Magali
authors.initials: M
authors.lastname: Allain
authors.forename: Ion
authors.initials: I
authors.lastname: Grosu
authors.forename: Jean
authors.initials: J
authors.lastname: Roncali
keywords: basic condensation; clean chemistry; donor-acceptor systems; organic solar cells; photochemistry