Simple and Versatile Molecular Donors for Organic Photovoltaics Prepared by Metal-Free Synthesis

• Published in: Chemistry : a European journal Vol. 21; no. 4; pp. 1598 - 1608
• Main Authors: Diac, Andreea, Demeter, Dora, Allain, Magali, Grosu, Ion, Roncali, Jean
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 19.01.2015; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc; Wiley-VCH Verlag
• Subjects: Absorption spectra; basic condensation; Buckminsterfullerene; Chemical Sciences; Chemistry; Chemistry, Multidisciplinary; clean chemistry; donor-acceptor systems; Doppler effect; Fullerenes; Molecular orbitals; organic solar cells; photochemistry; Photovoltaic cells; Physical Sciences; Red shift; Science & Technology; Solar cells; Spacers; Spectrum analysis; organic solar cells; HIGH-PERFORMANCE; POLYMERS; DESIGN; 3,4-ETHYLENEDIOXYTHIOPHENE EDOT; CONJUGATED SYSTEMS; CONVERSION; SEMICONDUCTORS; basic condensation; clean chemistry; donor-acceptor systems; photochemistry; CHEMISTRY; HETEROJUNCTION SOLAR-CELLS; BUILDING-BLOCK; Donor–acceptor systems; Clean chemistry; Organic solar cells; Basic condensation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201405425

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. Finding the right partner: Small push–pull molecules were synthesized in good yields by a three‐step metal‐free procedure. Thin films produced by both solution process and vacuum deposition led to interesting photovoltaic performances in simple bilayer heterojunction solar cells with C60 as the acceptor material.