• Energy Research

AbstractDonor–bridge–acceptor triad (Por‐2TV‐C60) and tetrad molecules ((Por)2‐2TV‐C60), which incorporated C60 and one or two porphyrin molecules that were covalently linked through a phenylethynyl‐oligothienylenevinylene bridge, were synthesized. Their photodynamics were investigated by fluorescence measurements, and by femto‐ and nanosecond laser flash photolysis. First, photoinduced energy transfer from the porphyrin to the C60 moiety occurred rather than electron transfer, followed by electron transfer from the oligothienylenevinylene to the singlet excited state of the C60 moiety to produce the radical cation of oligothienylenevinylene and the radical anion of C60. Then, back‐electron transfer occurred to afford the triplet excited state of the oligothienylenevinylene moiety rather than the ground state. Thus, the porphyrin units in (Por)‐2TV‐C60 and (Por)2‐2TV‐C60 acted as efficient photosensitizers for the charge separation between oligothienylenevinylene and C60.

AbstractFullerene derivatives functionalized with isomeric phenyleneethynylene‐based dendrons possessing either 1,3,5‐triethynylbenzene or 1,2,4‐triethynylbenzene branching units have been prepared. The electrochemical properties of these compounds are not strongly dependent on the branching patterns since the corresponding redox processes are localized either on the C60 cage (acceptor unit) or on the dialkyloxybenzene moieties (donor units) at the dendron periphery. The photophysical investigations performed in CH2Cl2 have revealed an ultrafast dendron → C60 energy transfer in all these hybrid systems. Importantly, the different π‐conjugation patterns in the two series have a dramatic effect on their electronic properties as attested by the differences observed in their absorption and emission spectra. The lower lying absorption onset and the wider spectral profile of the dyads with 1,2,4‐triethynylbenzene branching units when compared to their 1,3,5‐triethynylbenzene analogues clearly points out an improved light harvesting capability. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Two ruthenium sensitizers TT-230 and TT-232 based on cyclopenta[2,1-b:3,4-b']dithiophene (CDT) were tested in dye-sensitized solar cells (DSSCs) using,a tri-iodide/iodide redox couple, and their performances compared to the benchmark Z907. Both dyes of general formula Ru(LL')(NCS)(2) feature the same 4.4'-dicarboxylic acid 2,2'-bipyridine moiety acting as the anchoring group (L) to attach the dye on the TiO2 surface, and two CDT subunits as ancillary groups (L' either directly-linked (11-230) or vinylene-linked (TT-232) to the bipyridine moiety. In comparison with TT-230, the it-extended conjugation in TT-232 caused significant redshift and broadening of the absorption bands. However, despite better light-harvesting properties, the DSSC device sensitized with TT-232 strikingly underperformed compared to TT-230 under same conditions (PCE = 3.2% and 6.1%, respectively). The use of co-adsorbent (CHENO) or surfactants did not help to improve the photovoltaic properties of TT-230, and resulted in a degradation of the overall efficiency of the cell. (C) 2014 Elsevier Ltd. All rights reserved.

A novel star-shaped dye based on highly conjugated oligothienylenevinylene (nTV) bearing pendant solubilizing hexyl chains and end-capped with three tetramethylammonium cyanoacetates as anchoring groups has been synthetized. Its photovoltaic performance, in mesoporous TiO2 dye-sensitized solar cell, has been tested under different experimental conditions. The best performances were obtained at longer adsorption times of 4 h using different electrolyte compositions, reaching up to 3.11% of efficiency.

AbstractThe synthesis and characterization of two related families of star‐shaped thiophene‐containing hole‐transporting materials (HTMs) based on fused tetrathienoanthracene and nonfused tetrathienylbenzene cores are reported. All of them are endowed with four terminal (4,4′‐dimethoxy)diphenylamino groups that are either linked directly to the core or showed a different type of bridges (i.e., thiophene‐phenyl or phenyl rings). The novel HTMs are tested in mixed‐ion perovskite (Cs0.1FA0.74MA0.13PbI2.48Br0.39) solar cells, and power conversion efficiencies of up to 18.8% are measured under 1 sun irradiation, comparable with the efficiency obtained for the reference cell using 2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene as an HTM.

A family of four push–pull porphyrazines of A3B type, where each unit A contains two peripheral propyl chains and the unit B is endowed with a carboxylic acid, were prepared. The carboxylic acid was attached to the β-position of the pyrrolic unit, either directly (Pz 10), or through cyanovinyl (Pz 11) and phenyl (Pz 7) groups. The fourth Pz (14) consisted in a pyrazinoporphyrazine wherein the dinitrogenated heterocycle provided intrinsic donor–acceptor character to the macrocycle and contained a carboxyphenyl substituent. The direct attachment of the carboxylic acid functions and their linkers to the porphyrazine core produces stronger perturbation on the electronic properties of the macrocycle, with respect to their connection through fused benzene or pyrazine rings in TT112 and 14, respectively. The HOMO and LUMO energies of the Pzs, which were estimated with DFT calculations, show little variation within the series, except upon introduction of the cyanovinyl spacer, which produces a decrease in both frontier orbital energetic levels. This effective interaction of cyanovinyl substitution with the macrocycle is also evidenced in UV/Vis spectroscopy, where a large splitting of the Q-band indicates strong desymmetrization of the Pz. The performance of the four Pzs as photosensitizers in DSSCs were also investigated.