Antonio Cravino

Multi-donor molecular bulk heterojunction solar cells: improving conversion efficiency by synergistic dye combinations

Molecular bulk heterojunction solar cells with a power conversion efficiency of 1.70% have been fabricated using as donor BODIPY dyes with complementary light-harvesting properties.

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.

Origin of the open circuit voltage of donor-acceptor solar cells: Do polaronic energy levels play a role?

This letter analyzes the influence of the energy of the highest-energy occupied molecular orbital (HOMO) and the single occupied molecular orbital (SOMO) (i.e., the low-energy polaronic level) of different electron donors (D) on the open circuit voltage (VOC) value delivered by bilayer and bulk-heterojunction solar cells containing fullerenes as acceptor (A). The analysis further confirms that the VOC of these devices scales with the energy difference between the HOMO of the D and the lowest-energy unoccupied molecular orbital of the A. As observed, a better relationship is obtained if the SOMO energy of the D—extracted from photoinduced absorption spectra—is considered.

Effects of aromatic spacers on the properties of organic field effect transistors based on π-extended tetrathiafulvalene derivatives

OFETs built from extended TTF derivatives containing N-methylpyrrole, furan, thiophene and benzene with meta or para linkages as spacers are presented. The aromatic spacer plays a crucial role in the characteristics and stability of the OFETs. The less conjugated derivative with a meta-benzene moiety as spacer has the best mobility, with a higher on/off ratio and strongly enhanced stability in air.

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.