Small D–π–A Systems with o‐Phenylene‐Bridged Accepting Units as Active Materials for Organic Photovoltaics

Abstract

Donor-acceptor (D-π-A) systems that combine triarylamine donor blocks and dicyanovinyl (DCV) acceptor groups have been synthesized. Starting from the triphenylamine (TPA)-thiophene-DCV compound (1) as a reference system, various synthetic approaches have been developed for controlling the light-harvesting properties and energy levels of the frontier orbitals in this molecule. Thus, the introduction of methoxy groups onto TPA, the replacement of one phenyl ring of TPA by a thiophene ring, or the extension of the π-conjugating spacer group lead to the modulation of the HOMO level. On the other hand, the fusion of the DCV group onto the vicinal thiophene ring by an ortho-phenylene bridge allows for a specific fine-tuning of the LUMO level. The electronic properties of the molecules were analyzed by using UV/Vis spectroscopy and cyclic voltammetry and the compounds were evaluated as donor materials in basic bilayer planar heterojunction solar cells by using C60 as acceptor material. The relationships between the electronic properties of the donors and the performance of the corresponding photovoltaic devices are discussed. Bilayer planar heterojunction solar cells that used reference compound 1 and C70 afforded power-conversion efficiencies of up to 3.7 %.

DFT Study of Photoelectric Properties of Some Organic Polymers

“…Among the renewable energy sources the solar energy, practically inexhaustible, is by far the most available natural source of energy, clean and accessible at every point of the earth's surface [1,2]. It can therefore be an excellent solution to the problem of energy supply in the world and especially in the sunny geographical areas of the globe.…”

“…The photovoltaic effect is a phenomenon which consists in generating electricity by absorption and conversion of light energy into electrical energy. An organic solar cell consists of a layer of photoactive organic materials sandwiched between two electrodes [1,2]:…”

“…The transfer of charge to the Donor-Acceptor interface (D/A) is in competition with excitons recombination; only the excitons generated at a distance sufficiently close to the interface can reach the interface and be dissociated there before recombining. The critical distance is of the order of the diffusion length of the excitons (a few nanometers) [1][2][3][4][5].…”

“…In this stride, organic molecules or polymers are increasingly explored and used as semiconductor materials in the design of photovoltaic cells. However, in this scientific endeavor, one of the challenges still remains the improvement of the electrical conversion efficiency of these organic semiconductors [1][2][3]. The semiconducting properties of organic materials come from the alternation of single and double covalent bonds in their molecular structures [1][2][3][4][5].…”

“…However, in this scientific endeavor, one of the challenges still remains the improvement of the electrical conversion efficiency of these organic semiconductors [1][2][3]. The semiconducting properties of organic materials come from the alternation of single and double covalent bonds in their molecular structures [1][2][3][4][5]. This electronic conjugation which favors the delocalisation and the circulation of the electronic charges can then constitute a first criterion for the selection of the molecules likely to be involved in the design of an organic photovoltaic cell.…”