Juan-José Cid

Effect of Coadsorbent on the Photovoltaic Performance of Zinc Pthalocyanine-Sensitized Solar Cells

The effect of chenodeoxycholic acid as a coadsorbent on TiO 2 nanocrystalline solar cells incorporating phthalocyanine sensitizers was studied under various conditions. Adding chenodeoxycholic acid onto TiO 2 nanoparticles not only reduces the adsorption of phthalocyanine sensitizers but also prevents sensitizer aggregation, leading to different photovoltaic performance. The inspection of IPCE and absorption spectra showed that the load of phthalocyanine sensitizers is strongly dependent on the molar concentration of chenodeoxycholic acid coadsorbent. The open circuit voltage of the solar cells with chenodeoxycholic acid coadsorbent increases due to the enhanced electron lifetime in TiO 2 nanoparticles coupled with the band edge shift of TiO 2 to negative potentials.

Carboxyethynyl Anchoring Ligands: A Means to Improving the Efficiency of Phthalocyanine-Sensitized Solar Cells†

Keywords: conjugation ; electron transfer ; solar cells ; synthetic methods ; zinc ; Conversion Efficiency ; Porphyrin Sensitizers ; Tio2 ; Dyes Reference EPFL-ARTICLE-177266doi:10.1002/anie.201108963View record in Web of Science Record created on 2012-05-18, modified on 2016-08-09

Structure-function relationships in unsymmetrical zinc phthalocyanines for dye-sensitized solar cells.

A series of unsymmetrical zinc phthalocyanines bearing an anchoring carboxylic function linked to the phthalocyanine ring through different spacers were designed for dye-sensitised solar cells (DSSC). The modification of the spacer group allows not only a variable distance between the dye and the nanocrystalline TiO(2), but also a distinct orientation of the phthalocyanine on the semiconductor surface. The photovoltaic data show that the nature of the spacer group plays a significant role in the electron injection from the photo-excited dye into the nanocrystalline TiO(2) semiconductor, the recombination rates and the efficiency of the cells. The incident monochromatic photon-to-current conversion efficiency (IPCE) for phthalocyanines bearing an insulating spacer is as low as 9%, whereas for those with a conducting spacer an outstanding IPCE 80% was obtained.

Towards Tunable Graphene/Phthalocyanine–PPV Hybrid Systems†

The sheer explosion of interest in graphene has undoubtedly shown that it is the rising star in the emerging field of nanotechnology. Its extraordinary properties render it an outstanding material for electronics, material sciences, and photoconversion systems. As a zero-gap semiconductor for example, a flat monolayer of graphene is almost transparent and exhibits the lowest known electrical resistivity for any material at room temperature. The remarkably high electron mobility of graphene gives rise to its implementation in transparent conducting electrodes as a viable alternative to indium tin oxide (ITO). 4] Recent results demonstrate, however, that doping is a necessity to harvest the full potential of graphene. 6] Therefore, the aim herein is the tuning/altering of the features of photochemically transparent graphene by integrating a versatile electron donor system in solution. High-quality graphene flakes have been formed by means of solution processing, which involves exfoliating and dispersing them directly from graphite. 8] Such mild strategies stand in strong contrast to high throughput exfoliation of graphite with the assistance of strong oxidants. Moreover, reduction of graphene oxide to graphene is by no means quantitative and results in irreversible coagulation and permanent lattice defects. 13] To date, samples that exhibit high charge mobilities are large-area graphene samples obtained by micromechanical cleavage of pyrrolitic graphite. Other notable breakthroughs in this area rely on sheets grown onto solid substrates. The investigation of novel electron donor–acceptor hybrids involving low-dimensional allotropes of carbon is far more challenging than the exploitation of carbon nanotubes in the same context. The reason is primarily the lack of photospectroscopic signatures/markers, which makes the study of graphene more challenging. In fact, we have selected a spectator molecule to circumvent this impediment and to assist in identifying and visualizing electron donor–acceptor interactions. The unique absorption with high extinction coefficients in the red and near infrared regions, fluorescence, and the strong electron-donating character of zinc phthalocyanines (ZnPc) make a ZnPc-based PPV oligomer (1) PPV = poly(p-phenylene vinylene) the molecule of choice (Supporting Information, Scheme S1). Apart from supporting several ZnPc units, the oligomeric backbone is expected to be a great asset with regard to graphite exfoliation and stabilization of novel nanographene (NG) hybrids bearing ZnPc oligomer 1 that are thus formed (Figure 1).

Increasing the efficiency of zinc-phthalocyanine based solar cells through modification of the anchoring ligand

Several zinc-based phthalocyanines have been synthesized and used in Dye-Sensitized Solar Cells (DSSC). The results have been compared with the standard TT1 phthalocyanine, which shows good light-to-energy conversion efficiencies in comparison with other IR sensitizers used in DSSC. We show herein that the anchoring moiety is critical for both achieving high injection yields and slow back electron transfer dynamics that affect the overall device efficiency. Moreover, based on these results, we have synthesized a new phthalocyanine with a superior performance, when compared to the TT1 dye, with a subtle change on the anchoring moiety, thus leading to a higher photocurrent response.

Synthesis and Photophysical Properties of Fullerene–Phthalocyanine–Porphyrin Triads and Pentads

The synthesis and photophysical properties of several fullerene-phthalocyanine-porphyrin triads (1-3) and pentads (4-6) are described. The three photoactive moieties were covalently connected in an one-step synthesis through 1,3-dipolar cycloaddition to C(60) of the corresponding azomethine ylides generated in situ by condensation reaction of a substituted N-porphyrinylmethylglycine derivative and an appropriated formyl phthalocyanine or a diformyl phthalocyanine derivative, respectively. ZnP-C(60)-ZnPc (3), (ZnP)(2)-ZnPc-(C(60))(2) (6), and (H(2)P)(2)-ZnPc-(C(60))(2) (5) give rise upon excitation of their ZnP or H(2)P components to a sequence of energy and charge-transfer reactions with, however, fundamentally different outcomes. With (ZnP)(2)-ZnPc-(C(60))(2) (6) the major pathway is an highly exothermic charge transfer to afford (ZnP)(ZnP(.+))-ZnPc-(C(60)(.-))(C(60)). The lower singlet excited state energy of H(2)P (i.e., ca. 0.2 eV) and likewise its more anodic oxidation (i.e., ca. 0.2 V) renders the direct charge transfer in (H(2)P)(2)-ZnPc-(C(60))(2) (5) not competitive. Instead, a transduction of singlet excited state energy prevails to form the ZnPc singlet excited state. This triggers then an intramolecular charge transfer reaction to form exclusively (H(2)P)(2)-ZnPc(.+)-(C(60)(.-))(C(60)). A similar sequence is found for ZnP-C(60)-ZnPc (3).

Screening interactions of zinc phthalocyanine–PPV oligomers with single wall carbon nanotubes—a comparative study

In this paper, the ability to disperse single wall carbon nanotubes (SWNT) of several different-nature poly(p-phenylene vinylene) (PPV) oligomers having pendant zinc phthalocyanines (ZnPc) has been investigated. Based on the quenching of the ZnPc and SWNT fluorescence in the supramolecular assemblies, it has been shown that parameters such as p/n-type character of the oligomer, size and the distance between the ZnPc moiety and the conjugated backbone play an important role in the strength of the interactions. Important results suggest that n-type oligomers as well as certain flexibility in the phthalocyanine arrangement are breakthroughs for immobilizing SWNT in THF, affording stable and homogeneous suspensions. Transient absorption measurements confirm that upon photoexcitation the photoexcited ZnPc triggers an intraensemble charge transfer to yield oxidized ZnPc and reduced SWNT.

Charge separation in a covalently-linked phthalocyanine-oligo(p-phenylenevinylene)-C60 system. Influence of the solvent polarity.

A photo- and redoxactive system ZnPc-oPPV-C(60)2, in which the photoexcited state electron donor - zinc phthalocyanine - and the ground state electron acceptor - C(60) - are connected by a oligo(p-phenylenevinylene) (oPPV) spacer, has been synthesized in a multi-step synthesis by means of two consecutive Wadsworth-Horner-Emmons and a dipolar 1,3-cycloaddition reactions as key steps. The simpler system ZnPc-C(60)1 has also been prepared as a reference model for photophysical studies. In this regards, the photophysical investigations by means of fluorescence, flash photolysis, and transient-absorption spectroscopy have manifested a clear dependence between charge transfer kinetics and spatial arrangement. In both systems, intramolecular charge separation evolves from the photoexcited ZnPc and yields the ZnPc(·+)/C(60)(·-) radical ion pairs. Interestingly, the ZnPc(·+)/C(60)(·-) radical ion pair lifetimes and quantum yields are strongly impacted by the solvent polarity and the distance. To this end, maximum radical ion pair lifetimes of 2900 and 5530 ps were found in anisol for 1 and 2, respectively.

Synthesis and characterization of high molecular weight phthalocyanine-PPV copolymers through post-polymerization functionalization

High molecular weight poly(p-phenylenenevinylene) PPV copolymers laterally substituted with zinc (II) phthalocyanines (Zn(II)Pc-PPV 1 and 2) have been synthesized by means of post-polymerization functionalization reactions through DCC-mediated esterifications between hydroxy-phthalocyanines 4 and 6 and carboxy-bearer PPV copolymers, comprising 2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene (MDMO-PPV) and 1,4-(2-(5-carboxypentyloxy)-5-methoxyphenylenevinylene (CPM-PPV) units in a 9:1 (3) and 1:1 (5) ratio, respectively. The resulting copolymer 1 contains a 7 mol % of Pc molecules, while copolymer 2, which is isolated as the soluble fraction of the reaction with the starting 1:1 copolymer (namely having around 50% of COOH-containing monomeric units), holds a 9 mol % of zinc(II) phthalocyanines. 1 and 2 were fully characterized by 1H NMR, UV-vis and FT-IR spectroscopies.