9:00-12:30 Solar Energy Conversion. Chair: Prof. A. Zecchina. 9:00 9:05 E. Pelizzetti, Rector, Università di Torino Greetings and Opening Remarks

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1 Photoeffects at Semiconductors for Energy and Environment Torino, 31 October 2011 Aula Magna "Primo Levi" Facoltà di Scienze MFN dell'università di Torino Via P. Giuria, 7 High efficiency solar energy harvesting with low cost materials is a key necessity for a sustainable future. Photoeffects at semiconductor materials hold good potential for playing a central role in this field. However new schemes and paradigms are needed in order to enhance efficiency of these processes and lower the material costs. Organized in the framework of the celebration for the International Year of Chemistry, this workshop would summarize new promising approaches in order to exploit photoeffects at semiconductors for photovoltaics and photocatalysis. New generation of solar cells will be discussed with renowned international experts of the fields. New approaches for the enhancement of the efficiency of photocatalytic processes will be presented and discussed. 9:00-12:30 Solar Energy Conversion Chair: Prof. A. Zecchina 9:00 9:05 E. Pelizzetti, Rector, Università di Torino Greetings and Opening Remarks 9:05 9:10 A. Zecchina, Professor emeritus, Università di Torino Introduction 9:10 9:55 A. J. Nozik, NREL Golden Co, USA Approaches to Future Generation Photovoltaics and Solar Fuels: Multiple Exciton Generation in Quantum Dots, Quantum Dot Arrays, Molecular Singlet Fission and Quantum Dot Solar Cells 9:55 10:40 M. K. Nazeeruddin, EPFL Lausanne, Switzerland Molecular Engineering of Sensitizers for Mesoscopic Solar Cells 10:40 10:55 Coffee Break

2 Chair Prof. G. Viscardi 10:55 11:25 C. Carbonera, Istituto ENI Donegani, Novara, Italy Polymeric Solar Cells 11:25 11:55 M. Cossi, Università del Piemonte Orientale, Alessandria, Italy Ab Initio Modeling of PbSe Quantum Dots: Shape, Surface Passivation, and Interactions with Organic Dyes for Applications in Dye-Sensitized Solar Cells 11:55 12:25 C. Barolo, G. Viscardi, Università di Torino, Italy Unconventional Photosensitizers for Dye-Sensitised Solar Cells 14:00-18:00 Photocatalysis Chair Prof. C. Minero 14:00 14:30 G. Martra, C. Deiana, E. Fois, S. Coluccia, Università di Torino, Italy Hydration, hydroxylation and relative abundance of surface sites of TiO 2 nanoparticles: an IR, HR-TEM and ab-inito modeling approach 14:30 15:10 S. Livraghi, M. Chiesa, MC Paganini, E. Giamello, Università di Torino, Italy Band engineering in modified titanium dioxide by insertion of p-block elements 15:10 15:40 C. Minero, F. Sordello, Università di Torino, Italy Photocatalytic Metamaterials 15:40 15:55 L. Mino, G. Spoto, S. Bordiga, C. Lamberti, A. Zecchina, Università di Torino, Italy Surface properties and reactivity of TiO 2 nanocrystals 15:55 16:10 F. Cesano, D. Pellerej, G. Ricchiardi, D. Scarano, A. Zecchina, Università di Torino, Italy TiO 2 -based porous microspheres: synthesis, characterization and photocatalytic tests 16:10 16:25 Coffee Break Chair. Prof. G. Spoto 16:25 16:55 E. Selli, Università di Milano, Italy Effects of surface modification and doping on the photocatalytic activity of TiO 2 16:55 17:10 A. Damin, A. Budnik, S. Bordiga, A. Zecchina, Università di Torino, Italy From silica-titania to pure titania monoliths: synthesis and characterization 17:10 17:30 F. Canonico, Buzzi Unicem, Italy Photocatalytic Building Materials 17:30 17:55 V. Maurino, M. Minella, A.Bedini, E. Pelizzetti, C. Minero, Università di Torino, Italy Tuning TiO 2 photoactivity by playing with surface properties 17:55 18:00 Adriano Zecchina, Professor emeritus, Università di Torino, Italy Concluding Remarks

3 Contact and Informations: Prof. Valter Maurino Dipartimento di Chimica Analitica Università degli Studi di Torino Via Pietro Giuria 5, Torino ITALY phone , fax web International Year of Chemistry in Piemonte COMITATO ORGANIZZATORE Presidente, Prof. Emeritus Adriano Zecchina Università degli Studi di Torino - Dipartimento di Chimica IFM tel fax With the patronage of: Accademia Nazionale dei Lincei Accademia delle Scienze di Torino Centro UNESCO Torino Provincia di Torino With the sponsorship of: Compagnia di San Paolo Fondazione CRT Camera di commercio di Torino Unione Industriale di Torino Distretto 2030 Rotary Club Fondazione TERA Buzzi Unicem In co-operation with: Centro Scienza Società Chimica Italiana Regione Piemonte Centro internazionale di studi Primo Levi ASP Associazione per lo Sviluppo Scientifico e Tecnologico del Piemonte Istituto Donegani Polo per la Chimica Sostenibile

4 Approaches to Future Generation Photovoltaics and Solar Fuels: Multiple Exciton Generation in Quantum Dots, Quantum Dot Arrays, Molecular Singlet Fission, and Quantum Dot Solar Cells A. J. Nozik *, M.C. Beard, J.C. Johnson, M.C. Hanna, J. M. Luther, A. Midgett*, O. Semonin*, and J. Michl* National Renewable Energy Laboratory, Golden, CO 80401, USA *and Department of Chemistry, University of Colorado, Boulder One potential, long-term approach to more efficient future generation solar cells is to utilize the unique properties of quantum dots (QDs) and unique molecular chromophores to control the relaxation pathways of excited states to produce enhanced conversion efficiency through efficient multiple electron-hole pair generation from single photons. We have observed efficient multiple exciton generation (MEG) in PbSe, PbS, PbTe, and Si QDs and efficient singlet fission (SF) in molecules that satisfy specific requirements for their excited state energy level structure to achieve carrier multiplication. We have studied MEG in close-packed QD arrays where the QDs are electronically coupled in the films and thus exhibit good transport while still maintaining quantization and MEG.. We have developed simple, all-inorganic QD solar cells that produce large short-circuit photocurrents and power conversion efficiencies in the 3-5% range via both nanocrystalline Schottky junctions and nanocrystalline p-n junctions. These solar cells also show QYs for photocurrent that exceed 100% in the photon energy regions where MEG is possible; the photocurrent MEG QYs as a function of photon energy match those determined via time-resolved spectroscopy. We have also observed very efficient SF in thin films of molecular crystals of 1,3 diphenylisobenzofuran with quantum yields of 200% at the optimum SF threshold of 2Eg (HOMO-LUMO for S0-S1)), reflecting the creation of two excited triplet states from the first excited singlet state. Various possible configurations for novel solar cells based on MEG in QDs and SF in molecules that could produce high conversion efficiencies will be presented, along with progress in developing such new types of solar cells. Recent analyses of the effect of MEG or SF combined with solar concentration on the conversion efficiency of solar cells will be discussed.

5 M. K. Nazeeruddin EPFL Lausanne, Switzerland Molecular Engineering of Sensitizers for Mesoscopic Solar Cells

6 Polymer Solar Cells Chiara Carbonera Eni SpA Centro Ricerche per le Energie non Convenzionali Istituto Eni Donegani - Via Fauser 4, Novara Italy Thin-films solar cells based on organic and polymeric photoactive materials represent one of the most promising technologies to afford low-cost, readily available energy. In the recent years a large number of academic groups and industrial companies have started research programs aiming to find and develop new active materials and to optimize the device architectures; the final goal is to achieve efficient, durable and cheap solar cells that can enter the market of photovoltaics, especially for niche applications. Polymer solar cells (PSCs) are layered devices where a thin film ( nm) of a photoactive material is sandwiched between an anode and a cathode. In the state-of-the-art devices, the photoactive material consists of a blend of a conjugated polymer and a functional fullerene; the first component (electron donor) is able to absorb the sunlight and generate an hole-electron pair (exciton) which migrates toward the interface with the second component (electron acceptor) where it is dissociated, causing the transfer of an electron from the donor to the acceptor, provided that the energy levels of HOMO and LUMO are correctly matched. The donor-acceptor blend should exhibit a dispersed morphology (bulk heterojunction), where the interface between the two materials is maximized to favour the photoinduced electron transfer, but at the same time retains an interpenetrating network structure to assure percolating paths for the separated charges (holes and electrons) to reach the electrodes (anode and cathode, respectively). Usually, buffer materials are interposed between the active layer and one or both the electrodes. They are used to suppress charge recombination, to transport/block electron/holes, to tune the electrodes work function, to render more ohmic the active layer/electrodes interfaces, to act as optical spacers. The electrodes assure photogenerated charges collection and the difference of their work function is the driving-force for the charge carriers migration by generating a built-in potential. The cathode is usually a low work function metal (e.g. aluminium) or a metal pair (e.g. Ca/Al), whereas a high work function material is used for the anode. Transparent conductive oxides (TCOs), especially tin-doped indium oxide (ITO), are the most commonly used material to this end. One of the electrode must be transparent, to allow the light to reach the active layer. In most cases ITO is the transparent electrode, but very thin metallic layers (<20 nm) can also be employed for this purpose. Typical structure of a PSC is depicted in figure. As at least 10% efficiency is required for this kind of photovoltaic devices to enter the market, the optimization of PSCs is at the moment a hot topic. Materials research in this field focuses mainly on the preparation of materials with broad absorption, ideal energy levels matching, high charge mobility, controlled morphology, stability to oxidation, to be used as the photoactive layer. In the present lecture the state of the art and potential developments of this technology will be reviewed

7 Ab Initio Modeling of PbSe Quantum Dots: Shape, Surface Passivation, and Interactions with Organic Dyes for Applications in Dye-Sensitized Solar Cells M. Cossi Università del Piemonte Orientale, Alessandria, Italy DFT theory is used to compute the energy of different crystallographic faces of PbSe and the addition energies of several organic ligands, commony used as capping agents in nanocrystals synthesis. It is found that charged ligands can reverse the stability order of the PbSe faces, influencing the prevalence of one face and hence the final shape of the particle; this can also explain the excess of lead experimentally observed in PbSe quantum dots in some conditions. The addition to PbSe QD of organic dyes (cyanines) is studied for such systems have been proposed as efficient solar energy harvesters in dye-sensitized solar cells (DSC). Besides examining the preferred addition geometries and stability, the absorption/emission spectra of cyanine/qd complexes are predicted the TD-DFT level.

8 Unconventional Sensitizers for Dye-sensitised Solar Cells Claudia Barolo, Guido Viscardi Dip. di Chimica Generale e Chimica Organica and NIS Centre of Excellence, Università degli Studi di Torino, C.so M. d'azeglio 48, 10125, Torino, Italy claudia.barolo@unito.it, Tel.: The photosensitizer, as one of the crucial parts in dye-sensitized solar cells (DSCs), should fulfill some essential characteristics: (1) an absorption spectrum that cover the whole visible region and even the part of the NIR; (2) at least one anchoring group (-COOH, etc.) to strongly bind onto the semiconductor surface; (3) an excited state level higher in energy than the conduction band edge of n-type semiconductor (ntype DSCs); (4) an oxidized state level more positive than the redox potential of electrolyte; (5) photostability, and electrochemical and thermal stability Moreover unfavourable dye aggregation on the semiconductor surface should be avoided (optimization of dye molecular structure of the dye or addition of coadsorbers), but controlled dye aggregates (H and J) can, however, lead to an improved performance compared with a monomer dye layer. In order to fulfill all these requirements several molecular dyes as well as inorganic sensitizers have been designed and synthesized until now. Here we report some recent advances on unconventional sensitizers synthesized in the framework of the INNOVASOL EU project started in April 2009, i.e. symmetric low cost organic NIR dyes and quantum dots, as well as their interactions. Optical and photovoltaic properties will be presented showing their relationship with the chemical structure of the dyes.

9 Hydration, hydroxylation and relative abundance of surface sites of TiO 2 nanoparticles: an IR, HR-TEM and ab-inito modeling approach G. Martra, C. Deiana, E. Fois, S. Coluccia. Dipartimento di Chimica IFM and NIS Centre of Excellence, Università degli studi di Torino, Via P.Giuria 7, Torino Italy

10 Band engineering in modified titanium dioxide by insertion of p-block elements S. Livraghi, M. Chiesa, MC Paganini, E. Giamello Dipartimento di Chimica IFM and NIS Centre of Excellence, Università degli studi di Torino, Via P.Giuria 9, Torino Italy

11 Photocatalytic Metamaterials C. Minero, F. Sordello, Dipartimento di Chimica Analitica and NIS Centre of Excellence,, Università degli studi di Torino, via P.Giuria 5, Torino Italy The presentation will concern TiO 2 inverse opals, which belong to the family of tridimensional photonic crystals. After a brief introduction outlining the state of the art of the research on this kind of materials, the speech will focus on the study of the photocatalytic properties of these structures. From the analysis of the photoactivity of TiO 2 inverse opals emerges their status of metamaterials, since their properties arise principally from the 3D periodic structure and not from their chemical composition. The photoelectrochemical behaviour of TiO 2 inverse opals will be then presented to corroborate and complete the frame emerging from the photocatalytic treatment. Finally, the results of the modification of these materials with the addition of platinum will be presented.

12 Surface properties and reactivity of TiO 2 nanocrystals L. Mino, G. Spoto, S. Bordiga, C. Lamberti, A. Zecchina Dipartimento di Chimica IFM and NIS Centre of Excellence, Università degli studi di Torino, Via P.Giuria 7, Torino Italy Titanium dioxide is one of the most important metal oxides because of its applications as white pigment, as important component in solar cells and as photocatalyst [1]. In the last two applications the relevant phenomena are occurring at the surface of anatase nanoparticles, which are generally considered to be more active than rutile ones [2]. Therefore it is relevant for both technological and fundamental motivations to study the structure of the different surfaces terminating the anatase nanocrystals. In our work [3] we performed periodic DFT calculations of the structure of (101), (100), (001) and (112) anatase faces and of the vibrational properties of CO adsorbed on them at two coverages. Comparison of these results with HRTEM images of the adsorbing nanocrystals of P25 (a highly crystalline TiO2 characterized by outstanding photocatalytic properties and well shaped crystals) and with the experimental FTIR spectra of adsorbed CO on them at 60K (Figure 1) allowed to assign with unprecedented precision the complex spectrum of CO. The relevance of this achievement can be briefly described as follows. CO is a weak Lewis base and its stretching frequency changes when the molecule interact with the surface Ti 4+ sites since the greater is the electrophilicity of the metal cation, the higher is the blue shift with respect to the value in gas phase [4]. As the electrophylic character of Ti 4+ sites depends upon the face, the FTIR spectrum of adsorbed CO is composed by several peaks, each one corresponding to a specific facelet. On this basis it is evident that the IR spectrum give information about nanocrystals morphology and about the reactivity of different faces. To test the reactivity aspect, the water and acetylene adsorption has been studied. It is shown that the different faces are characterized by different reactivity. Acetylene is a special probe of the surface properties. In fact, unlike CO, it has acidic character and hence is able to probe the basic O2- ions present on the different faces. It is shown that acetylene is irreversibly interacting with basic sites with formation of colored oligomeric species. This reaction seems to be particularly interesting since these in situ grown acetylene polymers can act as potential sensitizers to improve the visible light photoactivity of TiO2. Figure 1. Band assignment in FTIR spectra of CO adsorbed at different coverages on highly dehydroxylated Degussa P25 nanocrystals. [1] A. Fujishima, X. T. Zhang, D. A. Tryk, Surf. Sci. Rep., 63, 2008, [2] U. Diebold, Surf. Sci. Rep., 48, 2003, [3] L. Mino, A. M. Ferrari, V. Lacivita, G. Spoto, S. Bordiga, A. Zecchina, J. Phys. Chem. C, 115, 2011, [4] K. I. Hadjiivanov, D. G. Klissurski, Chem. Soc. Rev., 25, 1996, 61-69

13 TiO 2 -based porous microspheres: synthesis, characterization and photocatalytic tests F. Cesano, D. Pellerej, G. Ricchiardi, D. Scarano, A. Zecchina. Dipartimento di Chimica IFM and NIS Centre of Excellence, Università degli studi di Torino, Via P.Giuria 7, Torino Italy Mesoporous TiO 2 microspheres with robust texture and high photoactivity, were prepared by inserting a TiO 2 -precursor in the confined space of polystyrene-co-divinyl benzene (PS-co-DVB) polymer, working as sacrificial scaffold. The impregnated polymer spheres, upon thermal treatments under N 2, N 2 /air or pure air flow at temperatures in the C interval, are transformed into porous microspheres. Depending on the gas flow composition, the obtained microspheres are constituted by porous carbon, hybrid core-shell C/TiO 2 or of cemented TiO 2 nanoparticles. The composition of pure TiO 2 microspheres ranges from pure anatase (400 C) to the prevailing rutile phase (500 C). All samples have been extensively characterized by means of SEM/AFM microscopies, N 2 -volumetric porosimetry, XRD and UV- Vis analyses. The photodegradation of NO has been used to check the photocatalytic activity of the TiO 2 - based materials. It is concluded that they exhibit higher photoactivity than the classical benchmark material (Degussa P25). This property together with the very robust and porous character of the microspheres, the tunable anatase-rutile ratio and the high cristallinity make these microspheres very interesting materials for applications in photocatalysis. From a physical point of view, the large axial pores and the columnar nature of the spheres can produce the entrapment of the light into the material.

14 Effects of surface modification and doping on the photocatalytic activity of TiO 2 E. Selli Dipartimento di Chimica Fisica ed Elettrochimica, Università degli Studi di Milano, via Golgi 19, Milano, Italy. elena.selli@unimi.it The photocatalytic activity of titanium dioxide prepared by different synthetic routes, including flame spray pyrolysis [1], and modified either by noble metal nanoparticles deposition or by surface fluorination, or by doping with non metal p-block elements [2-7] was tested in both down-hill and up-hill reactions, including the degradation of organic molecules in water suspension and the parallel hydrogen peroxide production by oxygen reduction [2] and hydrogen production from water splitting or methanol steam reforming [1,3,5,6]. Photoactivity results are discussed in relation to the structure and absorption properties of the photocatalytic materials, which may affect the photocatalytic electron transfer paths. Selected examples include the effect of gold nanoparticles deposition on the photocatalytic oxidation of organic substrates [2], the effect of fluorine doping on the absorption and action spectra of the materials [4,7], the effects of noble metal nanoparticles deposition [1,3] and of the inlet alcohol/water composition [3,6] on the reaction paths involved in the photo-steam reforming of methanol. 1. G.L. Chiarello, L. Forni and E. Selli, Catal. Today 144, 2009, M.V. Dozzi, L. Prati, P. Canton and E. Selli, Phys. Chem. Chem. Phys. 11, 2009, G.L. Chiarello, M.H. Aguirre and E. Selli, J. Catal. 273, 2010, M.V. Dozzi, S. Livraghi, E. Giamello and E. Selli, Photochem. Photobiol. Sci. 10, 2011, G.L. Chiarello, A. Di Paola, L. Palmisano and E. Selli, Photochem. Photobiol. Sci. 10, 2011, G.L. Chiarello, D. Ferri and E. Selli, J. Catal. 280, 2011, M.V. Dozzi, B. Ohtani and E. Selli, Phys. Chem. Chem. Phys. 13,

15 From silica-titania to pure titania monoliths: synthesis and characterization A. Damin, A. Budnik, S. Bordiga, A. Zecchina. Dipartimento di Chimica IFM and NIS Centre of Excellence, Università degli studi di Torino, Via P.Giuria 7, Torino Italy

16 F. Canonico Buzzi Unicem SpA, Italy, Photocatalytic Building Materials Among the industrial applications of photocatalysis, photocatalytic-modified construction materials play a major role: various materials are being developed, ranging from self-cleaning mortar or concrete facades to coatings. Recently we have seen considerable progress in the photocatalytic remediation of gas pollutants over road, as well as in the city environment. In this context, heterogeneous photocatalysis is now presented as an innovative technology for outdoor air remediation: TiO 2 incorporation in building materials and activation by the near-uv fraction of incident solar irradiation offers promising potential. Suitable amounts of TiO2 have been introduced into cement mixes to render the surface of the resulting structures photocatalytically active: these construction materials are claimed to maintain the aesthetic characteristics, the mechanical performances, and to clean the ambient air under the sunshine. Despite growing interest in the removal of micro-pollutants from ambient air by TiO 2 photocatalysis on building materials, only a limited number of systematically acquired experimental data are available so far and several optimistic-publications are presented, leading to possible misunderstandings of the real effect of such materials in controlling urban pollution. Several aspects must be analyzed before approaching the very attractive potential of photocatalytic cement. In spite of the various international standard available for the measure of the photo-activity, this point is still one of the most crucial and the (1) type and the efficiency of the reactor, (2) the measuring conditions (flow, temperature, moisture, irradiation) and (3) the way of expressing the results (photo efficiency) must be taken in account. Additionally, the estimation of the effects of photocatalysts in NO x pollution abatement in the real urban environment, requires an accurate simulation of transport phenomena in a given environment and are strongly dependent on the climate condition (sun radiation, wind). A overview of technological, economical and societal aspect regarding the implementation of photocatalytic building materials will be presented.

17 Tuning TiO 2 photoactivity by playing with surface properties V. Maurino, M. Minella, A.Bedini, E. Pelizzetti, C. Minero. Dipartimento di Chimica Analitica and NIS Centre of Excellence,, Università degli studi di Torino, via P.Giuria 5, Torino Italy The main limit to the practical application of heterogeneous photocatalysis has so far been the low photonic efficiency of current photocatalysts. Crucial issues are the efficiency in photogenerated charge carriers separation, the rate of interfacial charge transfer reactions, and the low absorption in the visible spectrum. It is widely recognized that the nature of the surface influences the processes of charge separation and electron transfer to organic substrates or water. Intrinsic surface properties such as the plane exposed, reconstruction and point defects, as well as extrinsic properties such as hydroxylation and the specific adsorption can affect the nature and the energetics of charge carrier surface traps. In the case of heterogeneous photocatalysis the dependence of the activity on surface properties is emphasized by the need of two reaction sites (electron and hole transfer). The distribution of the exposed surfaces of the photocatalyst is of paramount importance in controlling and optimizing the photoactivity. TiO 2 powders with relevant differences in the surface properties show very different photocatalytic activity and selectivity toward diverse substrates. The mechanism of photocatalytic degradation can change over different TiO 2 powders and as a result of surface complexation by fluoride or adsorption of cations, leading to a passivation of the surface. Recently we demonstrated that surface fluorination does not exchange all the surface hydroxyl groups, being bridged OH more resistant to exchange with F -. Differences in photoactivity and selectivity will be discussed in relation to the variations in particle morphology and in the populations of surface hydroxyls. The spatial separation of the oxidative and reductive processes on different crystallographic surfaces of irradiated TiO 2 will also be reviewed.