Instituto de Ciencia Molecular, Universidad de Valencia, PO Box 22085, ES-46071,

Valencia, Spain. E-mail: henk.bolink@uv.es

In the framework of ORION project, the “Instituto de Ciencia Molecular” of the University of Valencia is developing molecular optoelectronic devices employing ionic molecules and solution based processes. Using ionic absorbers, like cyanine dyes and fullerenes as charge donors and acceptors, respectively efficient double layer photovoltaic cells were prepared (Fig. 1). O. Malinkiewicz, T. Grancha, A. Molina-Ontoria, A. Soriano, H. Brine, H. J. Bolink, Adv. Ener. Mater.2013, asap. http://onlinelibrary.wiley.com/doi/10.1002/aenm.201200764/abstract


  Figure 1. Left: Device layout and the chemical structures of the materials employed. Right: current density versus voltage under simulated AM1.5 illumination.

Using ionic molecules electroluminescent devices were prepared in which an ionic transition metal is responsible for the electronic transport and light generation. Due to the ions efficient charge injection is achieved at low voltages. The ions decrease the injection barrier but need to dissociate and build-up at the electrode interfaces. This results in a rather slow turn-on of minutes to hours. It has been demonstrated by various methods that it is possible to decrease the time to turn-on, but always at the cost of the device stability. Current efficiencies in excess of 25 cd/A at a luminance of 700 cd/m2 were recently obtained. With a photoluminescence efficiency of 48 % these device efficiencies are close to the maximum obtained without special outcoupling efforts indicating the near perfect charge injection and recombination of this device (Fig. 2).


Figure 2.Layout of the LEC and the chemical structures of the ionic Iridium complex and the ionic liquid.

Carlos Fernandez-Solano, David Beljonne, Roberto Lazzaroni

University of Mons

The use of ionic liquids as electrolytes in dye-sensitized solar cells constitutes a major improvement over the classical liquid media, because of their electrochemical stability, combined with their lack of flammability and volatility. The ionic liquids are thus expected to interact with the surface of the oxide of the photoanode and it is essential to understand the structural and electronic properties of the oxide/ionic liquid interfaces.

In this context, we have undertaken a modeling study of a prototypical interface (TiO2/1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4)), with the Molecular Dynamics protocol we have recently developed for describing the structure and Li+ transport properties of ionic liquids.  The (110) face of the rutile phase was chosen to represent the TiO2 surface.

A snapshot representing the structure of the interface is shown in the figure below. The major conclusions from those simulations are that: (i) a very clear ion layering occurs at the oxide surface, with the BF4 anions forming a compact layer in direct contact with the surface; this is the result of the electrostatic attraction with the positively-charged Ti atoms; (ii) consistently, the next layer is

made of EMIM+ cations, followed by a second layer of BF4 ions; the plane of the EMIM ring is roughly parallel to the surface; (iii) this alternating layering extends over 20 Angstroms from the surface; (iv) as a consequence of the layering, the interface shows a strongly alternating charge density profile; (v) this organisation is independent of the temperature and ionic liquid density.


Figure 1. Snapshot for TiO2/EMIMBF4 interfaces at 393 K. The O, H, N, C, B, F, Ti atoms are drawn in red, yellow, blue, green, pink, cyan and purple colors, respectively.

Germà Garcia-Belmonte, Universitat Jaume I

Operating modes of electronic devices depend on the interplay between bulk (active layer) properties and contact features. How to discern internal (bulk) from contact effects is not a simple task when we are dealing with complete devices. In a solar cell good extracting contacts are desired in order to get the maximum photogenerated charge. But in many cases electrical response shows a mixed pattern that participates from both, internal and contact, influences. This entails that the quantification of the extraction ability of a given contact is masked by bulk transport. The strategy followed here blocks the carrier extraction by oxidation of the Ca cathode metal then revealing unambiguously bulk carrier diffusion, and consequently allows modeling the contact effect with additional circuit elements. More info in: J. Phys. Chem. C, 2012, 116 (32), pp 16925–16933 (http://pubs.acs.org/doi/abs/10.1021/jp305941f)


Stéphanie Narbey, Frédéric Oswald and Toby Meyer, Solaronix SA

Ionic liquids have been identified as a new class of solvents that offer opportunities to remove traditional solvent used in DSSC. Non volatility of ionic liquids makes them useful to prepare high stability electrolyte. Unfortunately, the major drawback is the high viscosity of these materials which lowers the efficiency of the devices. Mass transport limitation is usually the main issue with these systems. In order to improve the performance of the devices based on ionic liquid electrolyte, the porosity of the titania layer has been tuned using a new type of titana particles. The presence of micro channel in these new particles allowed enhancing the porosity of the layer while increasing the specific surface area. These improvements leaded to the preparation of high efficiency devices with PCE above 7%.


Elie Paillard, Dominic Bresser, Stefano Passerini

Institute of Physical Chemistry & MEET Battery Research Centre, University of Muenster,

Corrensstr. 28/30 & 46, 48149 Muenster, Germany

Conversion anodes were firstly introduced by Tarascon et al.[i] in 2000. Briefly, transition metal oxides (e.g. Co3O4, CoO, CuO, Fe3O4, Fe2O3, FeO, or NiO) are electrochemically reduced upon Li-ion battery charge, forming metallic nanoparticles finely dispersed in an amorphous Li2O matrix. Remarkably, this fine dispersion of the metallic nanoparticles enables the reversible formation of Li2O upon discharge, which has commonly been believed to be electrochemically inactive, leading in some cases to specific capacities of more than 1000 mAh g-1.

MOx + 2x Li+ + 2x e ↔ M0 + x Li2O

(M= transition metal, e.g. Co, Ni, Fe, or Cu)

Previous results have shown that the particle size is of primary importance for the cycling stability of such conversion materials,[ii] as a partially reversible formation of a polymeric layer on the particles surface, induced by electrolyte decomposition, is contributing to the obtained specific capacities, while at the same time leading to an increasing inner resistance.[iii] Thus, within the ORION project, Muenster University developed simple processes[iv] in order to prepare conversion material-based electrodes, starting from primary particles with an average diameter of around 20 nm, which originally exhibited a rather poor cycling stability. In particular, the formation of transition metal oxide nanoparticles/carbon composites resulted in a significantly improved electrochemical performance as well as in a simplified electrode processing. Indeed, the carbon coating, while enhancing the electrical conductivity within the electrode, ensures the confinement of the composite (Li2O + M0) particles, hence avoiding active material pulverization upon cycling. Moreover, the carbonaceous surface enables the formation of an efficient solid electrolyte interphase (SEI), thus reducing the electrolyte reactivity.

Encouraged by the good results obtained with conversion material-based nanocomposites, hybrid conversion-alloying nanomaterials, as for instance ZnFe2O4, have been subsequently investigated,[v],[vi],[vii] leading to the best results reported up to now, showing a stable specific capacity of around 1000 mAh g-1 and an advanced high rate capability, with capacities of around 525 mAh g-1 and 310 mAh g-1 for an applied specific current of 3.89 A g-1 and 7.78 Ah g-1, respectively (Figure 1). The main advantage of these materials, compared to pure conversion materials, is that once the metals are reduced, Zn can further alloy with lithium at lower potentials forming LiZn, thus resulting in an increased energy density relatively to pure conversion reactions, which usually operate at rather high potentials.

ZnxM1-xOy + (2y+x) Li+ + (2y+x) e↔ x LiZn + (1-x) M0 + 2y Li2O                          (0<x<1)


Another advantage as compared to alloying materials in general, is that Li2O acts as a buffering matrix for the volume change induced by the alloying reaction, as it has been already reported for other alloying materials, as for instance SnO2 or SiOx (x < 2). Although the cycling stability is certainly improved for such materials rather than for the elemental alloying materials, the first reduction of the alloying material is commonly irreversible in the absence of initially formed transition metal nanoparticles, which enable the reversible formation of Li2O.

More recent developments consisted in increasing the relative amount of the alloying element, switching from ZnFe2O4 to hybrid conversion-alloying materials with an increased Zn content (transition metal doped ZnO, having the general formula M0.1Zn0.9O) to decrease further the average voltage, while still enabling the reversible formation of Li2O.[viii] Simple synthesis methods were developed, starting form aqueous solutions, enabling the preparation of single nanoparticles with an average diameter of around 20 nm.

[i] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J-M. Tarascon, Nature (2000) 407, 496-499.
[ii] S. Grugeon, S. Laruelle, R. Herrera-Urbina, L. Dupont, P. Poizot, J-M. Tarascon, J. Electrochem. Soc. (2001) 148, A285-A292.
[iii] J.-M. Tarascon, S. Grugeon , M. Morcrette , S. Laruelle , P. Rozier ,P. Poizot , Co. R. Chim. (2005)  8 , 9-15.
[iv] E. Paillard, D. Bresser, M. Winter, S. Passerini, DE-10-2011-057-015.2.
[v] D. Bresser, E. Paillard, M. Winter, S. Passerini, DE-10-2012-101-457.4.
[vi] D. Bresser, E. Paillard, R. Kloepsch, S. Krueger, M. Fiedler, R. Schmitz, D. Baither, M. Winter, S. Passerini, Adv. Energy Mater. (2012) DOI: 10.1002/aenm.201200735.
[vii] F. Mueller, D.  Bresser, E. Paillard, M. Winter, S. Passerini,  J. Power Sources (2013) DOI: 10.1016/j.jpowsour.2013.02.051.
[viii] D. Bresser, F. Mueller, E. Paillard, M. Winter, S. Passerini, DE-10-2012-107-199.3.

In the framework of ORION project JHIPC, SOLVIONIC and CIDETEC explored a potential use of poly(hexafluorobutyl methacrylate) as the structure-directing agent in the synthesis of TiO2 films. The films were grown on glass, F-doped SnO2, and crystalline silicon (111) faces, either pure or with a thin layer of SiO2. This TiO2 film covers perfectly even rough surfaces, which was ascribed to thixotropic properties of the precursor gel.

Moreover, addition of phosphoric acid improves optical transparency and mechanical stability of the TiO2 films. The prepared films were compared to those templated by ionic liquids and  amphiphilic copolymers. The dense films show very good mechanical and chemical resistance. The optical properties are beneficial for antireflection coating on Si. The 40 nm thick film turned into a monolayer of anatase nanocrystals on Si-substrates upon calcination at 900°C. The newly developed synthetic technique produces dense TiO2 layers at relatively low temperature. Optical and mechanical properties of these films  may find some other practical applications.



Prochazka J., Kavan L., Zukalova M., Janda P., Jirkovsky J., Vlckova–Zivcova Z., Poruba A., Bedu M., Dobbelin M., Tena-Zaera R.: Dense TiO2 films grown by sol-gel dip coating on glass, F-doped SnO2, and silicon substrates, J. Mater. Res., 28, 385–393 (2013).

Laboratory of Photonics and Interfaces, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.


In dye-sensitized solar cells (DSC), the nanoparticle TiO2 dominates the performance, despite transport issues being faced due to defects at the interface between nanoparticles (see the bottom portion of figure, light blue dotted lines indicate the interface defects). In the colloidal form, the nanoparticles are individual moieties whereas after sintering their interfaces fuse to form electronic contacts. However, this ‘fusing’ induces significant electronic defect states. Following the electron injection from the excited state of the dye in DSCs, the transport of carriers are being hindered at these interfaces as indicated by the blue straight arrows in the bottom portion of the figure. To overcome this problem, most of the previous research works aimed at developing TiO2 nanotubes or nanorods or similar 1D structures, but the surface area available for the dye uptake is significantly less and hence efficiencies are predominantly low.

Here we propose a nice way to balance the transport and dye loading. The block diagram on the top portion of the figure explains the concept graphically.  Different thickness of TiO2 is deposited by atomic layer deposition (ALD) on an arbitrary mesoporous insulating template like SiO2, Al2O3 or ZrO2 and their photovoltaic properties are investigated. We discovered that just 6 nm TiO2 on the insulating mesoporous substrate is sufficient to transport the carriers efficiently. Also we found that, at any given charge density, the transport rate of photo-generated electrons are about one order of magnitude higher compared to the nanoparticle film. The reason being at the interface between nanoparticles, the electrons are scattered back due to defects whereas with the ALD conformal TiO2 these interparticle defects are absent.

One other impressive thing is that the ALD TiO2 itself can act as an underlayer to passivate the TCO. In the case of nanoparticle films, a separate underlayer is needed.

The faster percolation of charge carriers and reduction of film capacitance by using just 6 nm TiO2, with this new system can open up new path to explore high efficiency devices, respectively, in terms excellent charge collection and high open-circuit potential.

For more information, please read our recent publications in Advanced Functional Materials and ACS Applied Materials and Interfaces.