Nanoco Technologies in the ORION project

The main role of Nanoco Technologies in the ORION project is the scale up and supply of light sensitizers [quantum dots].

    

Nanoco’s CdSe reactor     Electron microscope image of Nanoco’s QDs

Nanoco’s standard QDs on offer to ORION partners include CdSe cores, CdS cores and CdSe/ZnS core/shell QDs.

Recently Nanoco has developed new synthetic methods to produce strong light QD absorbers in the NIR region.

New materials include CdTe and PbSeS. These are now available to the ORION consortium.

Impedance Spectroscopy: a useful tool for photovoltaic device characterization and modeling by Antonio Guerrero, and Germà Garcia-Belmonte

Photovoltaic and Optoelectronic Devices Group, Department of Physics, Universitat Jaume I, ES-12071 Castelló, Spain

It is commonly accepted that modeling an electrical system mainly consists of establishing a set of structural relations between suitable parameters which represent its electrical response. But in many cases, the role of instrumentation in the process of model construction is not explicitly acknowledged. Measurements are always a part of the model-creating process as modeling and measuring become parallel activities in practical terms. In the specific case of photovoltaic devices the sole current-voltage response contains poor information about the kinetic mechanisms limiting the solar cell performance. Impedance spectroscopy goes beyond static measurements by applying a small oscillating perturbation to a given steady state. Because the frequency of the oscillation is changed during the experiment separate structural parts of the device are able to electrically respond. This is why impedance can be regarded as a spectroscopy. Knowledge about functional materials, device structure, and impedance response should be combined to devise an electrical circuit which represents the electrical equivalent of the device response (more info about impedance courses by the group at http://www.hopv.org/ISSCHOOL11/ ).

Ionic liquids as solvents offer new opportunity to prepare active materials for electrode in Li-ion battery by Thibaut Gutel, CEA Grenoble

Since the introduction of Li-ion batteries on the market in 1990’s by Sony, worldwide researchers have been working to find active materials for electrode with better performances (capacity, cyclability, efficiency, self discharge,…), lower cost and safer (thermal stability,…) than conventional electrode material. The preparation of new inorganic-organic hybrid materials able to insert/deinsert Li ions in the structure is a new opportunity to improve electrochemical but also physico-chemical properties of lithium battery electrode. As an example, it has been demonstrated that the size of the active particles but also their morphology play an important role regarding their electrochemical properties. Consequently chemists have to develop new synthetic pathways in order to obtain active material with new and well-defined organization and recently ionic liquids have emerged as a very promising solvent in order to obtain pure materials with new morphologies.
Due to its large background in lithium batteries, Laboratory of Materials for Batteries (CEA Grenoble) is involved in the evaluation of electrochemical properties of the new hybrid materials which are synthesized during the project.

The new active material is mixed with a binder and a conductive additive and coated on a metal sheet to form an electrode. This electrode is integrated in a coin cell assembly and electrochemically characterized by cycling on a battery testing system.

Are Ionic Liquids (IL) good electrolytes for Li diffusion in batteries? A Molecular Dynamics study by Carlos Fernandez, Sergiu Clima, David Beljonne, and Roberto Lazzaroni, University of Mons

Ionic Liquids have emerged as the most promising candidates for use as Li battery electrolyte because of their negligible vapor pressure, low flammability and large electrochemical window. The questions that need be addressed are: how fast will the Li+ ions be able to diffuse in IL ? Will the IL represent a “bottleneck” or will it sustain high enough Li flow rates for the available cathode capacities? What is the optimum concentration of the anions that in principle can slow down the Li+.

In the present study we investigate the Li diffusion in a number of ionic liquids mixed with LiTFSI in different ratios, employing the state-of-the-art, many-body, polarizable APPLE&P force field for IL. The predicted self-diffusion coefficients, conductivity, and viscosity provided by simulations will be confronted with the experimental results to consolidate the predictive power of the selected approach for further IL-Li compositions refinements.

Molecular design of the improved structural and optical properties of new DSSC Ru dyes from first principles by Sergiu Clima, David Beljonne, Roberto Lazzaroni, University of Mons

Up to date the well renowned N719, N3 or C101 Ru(II) complexes are the most efficient ( more than 11%) Dye Sensitized Solar Cells (DSSC) photosensitizers. The aim of this work is to find new complexes with higher light-harvesting ability in tandem with the iodine redox system. For this purpose the First Principles approach is a valuable tool to assess the structure and the absorption spectrum of the newly synthesized, or of just to-be-synthesized newly designed Ru complexes, that show larger spectral absorption window and optimized position for the frontier orbitals.

Our DFT approach proves to be very useful in analyzing the electronic structure of well-known complexes and the gathered knowledge is exploited to design new dyes awaiting to be proven experimentally to have a higher efficiency.

Improvements in ionic liquid templated TiO2 films via modifications of the precursors by Jan Prochazka and Ladislav Kavan, JHIPC

J. Heyrovsky Institute of Physical Chemistry of the ASCR, v. v. i.
Dolejškova 2155/3, 182 23 Prague 8, Czech Republic

In the framework of ORION project JHIPC, LCPO-CNRS and SOLVIONIC explored a potential use of ionic liquids as a template in the synthesis of TiO2 films.
The work showed an important pathway to better utilizing the space within the nano-TiO2 network. If confirmed, this might increase the efficiency of the Dye Sensitized Solar Cell.
We also conducted systematic research on the precursors used for dip coating in the preparation of TiO2 films and of the parameters utilized. A variety of solutions with organic templates supplied from our partners were modified by using aqueous or non-aqueous solvents, adjusting the pH, or addition of H3PO4.
Although all data have not been analyzed yet, there is an apparent and very consistent difference in the film quality after addition of very small amounts of phosphoric acid to the solutions. A significant improvement after H3PO4 addition was observed for all ionic liquids and co-polymers used in the study. Phosphoric acid also significantly reduced hydrolysis of Ti-precursors, stabilizing them.

Picture 1.  Templated TiO₂ precursors (from the left)

Traditional recipes:

IL) MOIC = methyl-3-octylimidazolium chloride, A) PIL: PEO-PIL 1 (imidazolium acrylate, short block), B) BMIC = 1-butyl-3-methylimidazolium chloride SOLVIONIC, C) PEO-PIL 3 (imidazolium acrylate, long block), D) PEO-PIL 1 (N-vinyl imidazolium, long-block), E) PIL-PVP 1 (short N-vinyl imidazolium block), F) PIL-PVP 2 (long N-vinyl imidazolium block), G) DIB = dodecyl imidazolium bromide

Modified recipes:

M)   1) BMIC in Ethanol  → 2) + HCl, → 3) + H₃PO₄

I)     1) DIB in Butanol → 2) + HCl, → 3) + H₃PO₄

II)    1) PEO-PIL 1 in Butanol→ 2) + HCl, → 3) + H₃PO₄

III)   1) BMIC in Butanol → 2) + HCl, → 3) + H₃PO₄

IIIA) 1) BMIC in Butanol → 2) + H₂O

IIIB) 1) BMIC in Butanol → 2) + H₂O → 3) + H₃PO₄

Phosphoric acid provided better optical transparency and mechanical properties to the TiO₂ films and better characteristics to the ionic liquid and copolymer templated organometallic precursors.

This effect can be directly used in the production of solar cells and preparation of TiO₂ films for variety of uses.

ZnO electrodeposition in ionic liquid based electrolytes: an innovative route to obtain ZnO with special properties by Eneko Azaceta (CIDETEC), Sébastian Fantini (Solvionic), and Ramón Tena-Zaera (CIDETEC)

New Materials Department, CIDETEC, Centre for Electrochemical Technologies, Parque Tecnológico de San Sebastián, Paseo Miramón 196, Donostia-San Sebastián 20009, Spain
Solvionic, Chemin de la Loge, Toulosse 31078, France

In the framework of ORION project, CIDETEC and SOLVIONIC put together their wide expertise in electrochemical processes and ionic liquid synthesis to develop an innovative ZnO deposition route. The approach is based on the electrochemical reduction of O2 in an aprotic room temperature ionic liquid containing Zn2+ cations. The aprotic character of the ionic liquids is essential to avoid any interference and/or intermediate step related to metal hydroxide phases, which generally occurs in aqueous media. ZnO films are thus formed by a new reaction way. In addition, the interaction between ionic liquid moieties and ZnO surfaces seem to play a crucial role in the deposition mechanism, affecting the packing and ordering of ZnO nanocrystals. As a result, unusual non-polar oriented ZnO nanocrystalline films have been obtained. The films exhibit semiconducting behavior and room temperature photoluminescence emission.

All in all, the great potential of ionic liquids based electrolytes for the electrodeposition of functional optoelectronic ZnO nanocrystalline thin layers with innovative microstructural properties has been demonstrated. The present results may have a significant impact in several fields because the electrodeposition approach may be extrapolated to other metal oxides.

Colloidal nanocrystals and ionic liquid based hybrid nanostructures by CNR-IPCF

The role of CNR-IPCF in the Orion project regards mainly the fabrication of novel organized hybrid architectures formed of nanoparticles (NPs) in presence of ionic liquids (ILs) as structure directing agents.
The activity of CNR IPCF are focused on the study and the characterization of the nanostructured building blocks as well as of the resulting original hybrid materials for emerging applications in energy field.

In this frame, colloidal chemical strategies for nanomaterial synthesis have demonstrated to provide remarkable results in terms of size monodispersion (σ ≤ 5%), crystalline quality and tunability of size, shape and surface chemistry. In particular, these synthetic tools provide nanocrystals (NCs) which are coordinated, at their surface, by organic surfactant molecules which allow for treating them basically as macromolecules, thus conferring to the nano-objects an excellent processability. Such an organic surface layer can be further modified by post-synthetic treatments, thus providing an adjustable chemical interface with the surrounding environment that can be properly engineered, ultimately enabling a specific NC surface chemistry.

Currently, starting from the synthesis of colloidal oxide, such as TiO2 and semiconductor NCs, such as CdSe and PbS (Fig. 1), an extensive investigation on the optical properties of hybrid systems obtained incorporating the inorganic nanostructures in ILs is performed in order to study the effect of structural parameters in the IL (i.e. chain length and counter-ion) on eventual charge transfer mechanism occurring between nanoparticles and ILs.

Fig. 1: TEM pictures of PbS and CdSe NCs and TiO2 nanorods

In addition strategies to promote the charge transfer between semiconductor NCs (used as inorganic sensitizer) and oxide NPs are under investigation for their applications in NC sensitized Solar Cells.

On the use of nanoparticles as insertion materials for lithium ion batteries by Elie Paillard, Universität Münster

Principle of a lithium ion battery. Lithium Ion batteries are composed of two electrodes separated by an electrolyte. During the charge of the battery, Li+ cations are deinserted from the positive electrode and inserted into the negative electrode, circulating through the electrolyte, the driving force being the applied voltage or current which provides the electrons through the external circuit. The insertion/deinsertion reactions can be written as follow:
Li+ + e- + <> = <Li>

<> representing an empty site for Li+ capable of changing its oxidation state by accepting or releasing an electron, to accommodate the insertion/deinsertion of Li+.

The electric energy is thus converted into chemical energy, which is not released as long as the external circuit is open, as the electrolyte is a pure ionic conductor and does not allow the electrons to go from one electrode to the other. When the external circuit is closed, the battery is allowed to release the stored energy and the inverse reactions take place.The potential ranges at which these reactions occur at each electrode, determine the operating voltage of the battery, and the amount of lithium the materials are capable of hosting determines its capacity. The energy stored is the product of the operating voltage by the capacity.

Transport limitations-potential gradients. These two parameters depend on the current that the battery delivers, as a result of transport limitation of Li+ ions, either within the active materials or the electrolyte. Electronic conductivity of the materials also plays a role, especially in the case of non metallic compounds as potential gradients exist in the electrode and the potential of the current collector seen by the external circuit differs from the potential at which the electrochemical reaction take place in the electrode, even at 0 current. During battery operation, when current flows through the materials, ohmic drop induces further increase in the internal resistance. As a result, we observe a decrease in capacity and operating voltage when the battery delivers increasing current, and when high current are needed for high power applications (electric vehicle) the energy delivered by the battery decreases.

Use of composite electrodes. To facilitate these electronic and ionic transports, battery electrodes are not made of bulk materials simply connected to a current collector, but composed of particles of active material, an electronically conductive agent (carbon) and a polymer binder, to ensure the cohesion of the porous composite electrode. This results, in the ideal case, in each particle being in contact with the percolating electron conductive network, which reduces the electronic transport limitation in the whole electrode so that the electronic limitation happen only within each active particle. Finally, it decreases the path length of Li+ in the active material, all the more than the dimension of the particles is small.

Use of nanoparticles. In most cases, the limiting factors are the transport phenomena within the active material, which depends on the size of the particles; it is then easy to understand that downsizing the particle results in better performance of the battery, especially at high current.However, the advantages of using nanoparticles are not limited to a better rate capability, as the properties of these particles can differ significantly from the bulk materials, which in some cases results in higher lithium storage capability. Thus, the use of nanoparticles can enhance both the energy and power of lithium ion batteries.

This is why one goal of ORION is to improve battery performances by using nanoparticles. Some partners (Johnson and Matthey, CNR-ICPF) are involved in the synthesis of nanosized active materials, both for anode and cathode, with various chemistries, while CEA-LITEN and University of Muenster are in charge of evaluating the performances of the materials for use in lithium ion batteries. More than 10 different materials were evaluated in Muenster so far, and some gave interesting results, in terms of capacity or rate capability. Results will be presented on this blog later due to confidentiality reasons.

An example of the use of device modeling for improving solar cell operation by Germà Garcia-Belmonte, Universitat Jaume I.

Measuring I-V curve allows determining the operating parameters of a solar cell, especially the conversion efficiency. The problem is that the sole I-V curve (static characterization of the device) is unable of giving us useful information about the causes reducing functionality. The total device resistance is related to the derivative of the I-V curve, and this resistance has in principle more than just one contribution. For instance resistance placed in series (not directly related to the photovoltaic action) might have a significant detrimental impact. As drawn in the next figure increasing the series resistance has the effect of destroying the solar cell performance.

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Device modeling enters the scene aiming at decomposing separate contributions to the total resistance. The upper picture allows distinguishing contributions to the series resistance coming from transport and interfacial mechanisms. This is an example of device modeling applicable to dye-sensitized solar cells at forward bias. The extraction of each contribution to the total resistance is experimentally feasible by using impedance spectroscopy techniques. We see then that the interplay between measuring and modeling might imply substantial operation improvement by identifying limiting processes, in this particular case limiting transport processes.