Eugenia Martínez-Ferrero

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.

Quantum Dot-Dye Bilayer-Sensitized Solar Cells: Breaking the Limits Imposed by the Low Absorbance of Dye Monolayers

Here, we present a new DSSC design, consisting of sequential QDs and dye sensitization layers, that opens the path toward high optical density DSSCs that cover a significant part of the solar spectrum. The new configuration is enabled by the application of an amorphous TiO2 layer between the two sensitizers, allowing both electron injection from the outer absorber and fast hole extraction from the inner sensitizing layer. Utilizing two sensitizing layers, we obtain a 250% increase in cell efficiency compared to a QD monolayer cell.

Interfacial charge recombination between e(-)-TiO2 and the I(-)/I3(-) electrolyte in ruthenium heteroleptic complexes: dye molecular structure-open circuit voltage relationship.

A series of heteroleptic ruthenium(II) polypyridyl complexes containing phenanthroline ligands have been designed, synthesized, and characterized. The spectroscopic and electrochemical properties of the complexes have been studied in solution and adsorbed onto semiconductor nanocrystalline metal oxide particles. The results show that for two of the ruthenium complexes, bearing electron-donating (-NH2) or electron-withdrawing (-NO2) groups, the presence of the redox-active I(-)/I3(-) electrolyte produces important changes in the interfacial charge transfer processes that limit the device performance. For example, those dyes enhanced the electron recombination reaction between the photoinjected electrons at TiO2 and the oxidized redox electrolyte. In an effort to understand the details of such striking observations, we have monitored the charge transfer reactions taking place at the different interfaces of the devices using time-resolved single photon counting, laser transient spectroscopy, and light-induced photovoltage measurements.

Dye mediated charge recombination dynamics in nanocrystalline TiO2 dye sensitized solar cells

Dye-electrolyte interactions play an important role in mediating the recombination between injected electrons in the TiO2 electrode and the iodide/tri-iodide red-ox electrolyte in Dye Sensitized Solar Cells. This reaction reduces both cell voltage and efficiency and controlling it is therefore key to optimization and stability of such devices. This highlight will focus on experimental methods developed to monitor these recombination processes in functioning cell devices. Moreover, we discuss how certain dye structures seem to greatly accelerate recombination, in particular, in the case of highly conjugated sensitizers. Greater understanding of dye-interactions and ways to minimize them will help in the design of new sensitizers that show negligible recombination ultimately leading to optimization of cell efficiency.

Towards industrialization of polymer solar cells: material processing for upscaling

In this review, we provide insights into the key aspects of material processing for the industrialization of organic solar cells using printing solutions. The manuscript details the adjustments found in the literature about ink formulation and deposition parameters required to scale up the model system based on P3HT:PC60BM, from spin coating to doctor blade or inkjet printing and finally to roll-to-roll deposition. We analyze the particular problems associated with each technique in combination with the common problems linked to the choice of the procedure like the material consumption, the presence of inhomogeneities or time expenses. Moreover, we highlight the use of non-hazardous chemicals and the achievements done in upscaling technology which is nowadays a major topic in the construction of affordable light conversion devices.

The role of para-alkyl substituents on meso-phenyl porphyrin sensitised TiO2 solar cells: control of the eTiO2/electrolyte+ recombination reaction

We aim to investigate the effect of adding hydrophobic alkyl chains substituents to unsymmetrical free base tetra-phenyl porphyrins used for the preparation of dye sensitised solar cells (DSSC). We have used two different unsymmetrical meso-tetraphenyl substituted free base porphyrins attending to two objectives: (1) to observe how the substitution of three para positions of the meso-phenyl groups with hydrophobic alkyl chains influences the formation of molecular aggregates onto the semiconductor nanoparticles and (b) to deduce the influence that the substitution exerts over the eTiO2/electrolyte+ recombination reaction in operating devices. To achieve these goals we have focussed on the study of the electron transfer processes that take place at the different interfaces of the photovoltaic device using electrochemistry, steady-state and time resolved spectroscopic techniques.

Charge transfer kinetics in CdSe quantum dot sensitized solar cells.

We report the charge transfer dynamics for CdSe quantum dot (QD) sensitized solar cells. The effect of QD sensitization mode in recombination kinetics has been measured and their implications in solar cell performance analyzed.

The effect of molecular aggregates over the interfacial charge transfer processes on dye sensitized solar cells

The electron transfer reaction between the photoinjected electrons in the nanocrystalline TiO2 mesoporous sensitized films and the oxidized electrolyte in dye sensitized solar cells (DSSC) plays a major role on the device efficiency. In this communication we show that, although the presence of molecular aggregates on the free base porphyrin DSSC limits the device photocurrent response under illumination, they form an effective hydrophobic barrier against the oxidized electrolyte impeding fast back-electron transfer kinetics. Therefore, their drawback can be overcome by designing dyes with peripheral moieties that prevent the formation of the aggregates and are able to achieve efficiencies as high as 3.2% under full sun.

Interfacial charge transfer dynamics in CdSe/dipole molecules coated quantum dot polymer blends

We report our results on the influence of the dipole moment of small molecules anchored to the surface of CdSe nanocrystals, over the interfacial charge recombination dynamics in CdSe/P3HT (P3HT : poly-3-hexylthiophene). The polarizability of the CdSe/P3HT interface is key to achieving efficient charge separation and slow back electron transfer, two of the most important processes to boost the photocurrent and voltage in CdSe/P3HT photovoltaic devices.

Multifunctionality in hybrid molecular materials: Design of ferromagnetic molecular metals

Here we report recent advances in connection with the design, crystal structures and physical properties of novel hybrid organic-inorganic molecular materials combining ferromagnetic bimetallic oxalato-based networks and organic radicals of the tetrathiafulvalene (TTF) family, including the selenium and oxygen analogs.