1. Research Objectives/Activities
The research is focused on the investigation of nanotechnology driven photo-induced processes and their application to the direct conversion of solar energy into electricity as well as to environmental protection and health safety. More specifically it includes: ● Perovskite Solar Cells (PSCs); Dye-sensitized Solar Cells (DSCs); Quantum Dot Solar Cells (QDSCs) ● Photocatalysis ● CO2 storage and conversion
2. Activities and Main Results
2.1 Third Generation Solar Cells This work concerns the preparation and characterization of planar and mesoscopic perovskite as well as dye sensitized solar cells with high efficiencies. Preparation of mesoscopic nanocomposite semiconducting materials (powders, colloidal solutions) and thin films with optimum morphological characteristics (mainly high surface area) is searched via sol-gel chemistry. The research further aims at the manufacture and optimization of robust photoelectrodes using various deposition techniques (screen-printing, doctor-blade, spin-coating, dip-coating). Growth of titania nanotubes via hydrothermal autoclave treatment as well as self-organized nanostructures via anodic oxidation of Ti metal in corrosive aqueous or organic environments is investigated, too. Moreover, synthesis of new sensitizers (transition metal complexes and organic dyes), nanocrystalline semiconductors (quantum dots), or new perovskite materials with powerful absorption in the visible spectrum and enhanced hole mobility is also performed. Other activities include the development of solidified and ionic liquid based redox electrolytes (both iodide and cobalt complex based) and the study of their optical, photophysical and electrochemical properties. Besides, applied research on the development and optimization of solar cells that present high efficiency, increased stability and long life time is carried out by combining microscopy (SEM, AFM), spectroscopy (micro-Raman, FTIR) and electrochemical techniques (EIS, IMPS, IMVS).
2.1.1 Perovskite Solar Cells
The organic−inorganic methylammonium lead iodide (CH3NH3PbI3) hybrid and the partially chlorine-substituted mixed halide CH3NH3PbI3-xClx analogue have been prepared and compared as light harvesters in perovskite solar cells (PSCs). To account for the perovskites sensitivity in moisture, their stability was investigated by exposure in ambient atmosphere and the observed differences are discussed in terms of the materials vibrational properties and the device performance (J. Surf. Interface Mater., (2014) 2, 323-327). The structural and electronic properties of CsSnI3 as well as CH3NH3PbBr3-xClx - CH3NH3PbI3-xBrx have been studied by Raman and photoluminescence spectroscopies (HOPV15 Confer Rome May 2015).
2.1.2 New Organometallic Dyes for DSCs
A novel heteroleptic ruthenium-based light-harvesting antenna coordinated with a phenyl-anthracene-substituted terpyridine, a bipyridine, and a NCS ligand was synthesized and completely characterized (Asian J. Org. Chem. (2014) 3, 953-962).
2.1.3 Nanotubular Titania Electrodes
Self-assembled highly ordered TiO2 nanotubes arrays were grown on Ti foils in organic electrolytes (Chem. Engin. J. 224 (2013) 121 - Electrochim. Acta 113 (2013) 490). A variety of parameters was controlled and optimized including anodization growth conditions (potensiostatic, galvanostatic or combined methods) and post treatment conditions (annealing temperature, duration and heating rate) .
2.1.4 Blocking recombination in DSCs
A better insight on the positive effect of chenodeoxycholic acid (CHENO) when used as additive in cobalt based electrolytes employed in DSCs sensitized with the Z907 Ru(II) dye (Polyhedron (2014) 82, 109-115).
2.1.5 Low-viscosity Solvent-free Ionic Liquid-based Electrolytes
CnC1im]I/EMimDCA double salt Ionic liquid mixtures presenting low viscosity and high conductivity were used for the preparation of redox active electrolytes that were successfully incorporated in highly efficient dye-sensitized solar cells (J. Mater. Chem. A (2014) 2, 15326-15336).
2.1.6 DSCs’ Thermal Ageing
Robust Dye Sensitized Solar Cells have been prepared employing liquid electrolytes using tetraglyme and ethyl isopropyl sulfone (EiPS) high boiling point solvent. The cells with EiPS expressed high durability under harsh thermal stressing conditions of 85oC and prolonged ageing time, 3000 hours in the dark. (J. Phys. Chem. C 117 (2013) 8636-8646; Electrochimica Acta (2015), DOI: 10.1016/j.electacta.2015.03.206).
Advanced oxidation processes (AOPs) driven by photoinduced heterogeneous reactions that take place at the semiconductor/liquid and /gas interfaces are investigated. Special emphasis in given to the growth of innovative nanostructured titania photocatalysts and their application in the re-establishment of the environment (water, air) and the protection of health. Efficiency of the photocatalytic activity is improved via: a) control of the photocatalytic materials properties in the nano-scale level, b) increase of the photocatalyst effective surface area c) efficient separation of the photoinduced electron and hole carriers d) photocatalytic sensitization of the nanocatalyst in order to shift absorption onset in the visible by metal and non-metal doping, e) judicious balance of the photocatalytic and superhydrophilic properties in films which inherent self-cleaning functionality and f) immobilization of the nanocatalyst powders in complex photocatalytic films with increased chemical and mechanic stability. This research includes the development of antipollution technology and its application in the photochemical decomposition of harmful organics, killing of bacteria and viruses as well as growth of biofilms. Thus innovative composite photocatalytic nanomaterials are developed with parallel design and development of photocatalytic reactors for water and air treatment as well as the development of photocatalytic self-cleaning materials/coatings for the construction sector. Anion modified/doped titania is employed in combination with carbon nanotubes and membranes (micro- and ultra-filtration) for the photocatalytic decomposition of harmful organic pollutants under visible light illumination. In addition, the photocatalytically induced anticancer and anticoagulant action of titanium dioxide nanomaterials on neoplasm and inflammatory cells is also examined.
2.2.1 Visible Light Photocatalysis
The development of visible-light-active photocatalysts based on titanium dioxide has been investigated due to its wide range of applications in energy and environment related fields. Various strategies have been designed to efficiently utilize the solar radiation and to enhance the efficiency of photocatalytic processes (J. Phys. Chem. Lett. (2014) 5, 2543-2554).
2.2.2. Photocatalytic reactor for water purification under visible light
Visible light active photocatalytic ultrafiltration (UF) membranes have been developed by dip coating of γ-alumina membranes in a N-modified titania sol. The sol impregnates inside the membrane and covers the pore surface lending hydrophilic properties and resulting to high water flux (Catalysis Today (2014) 224, 56-69).
2.3 CO2 Storage and Conversion
The outgoing research focuses on physicochemical processes of both energy and environmental impact. New titania based nanomaterials and devices are developed for CO2 conversion (photoinduced reduction path) to useful chemicals (e.g. hydrocarbons). In parallel, innovative ionic liquids and metal organic frameworks are investigated for CO2 storage, with special interest given to host-guest interactions studied by in-situ Raman Spectroscopy. Carbon nanotube functionalization is performed and nanotechnology based modified electrodes and electrochemical sensors are developed for direct monitoring of harmful pollutants in water.
2.3.1 Interaction of CO2 with ZIFs
Zeolitic imidazolate frameworks are investigated by in-situ Raman spectroscopy in the practical temperature and CO2 pressure regimes (0-64 oC and 0-10 bar). Raman stands as an easy and sensitive tool for quantifying CO2 uptake, identifying weak host-guest interactions and elucidating CO2 sorption mechanism (ChemSusChem (2014) 7, 1696-1702).
2.3.2 CO2 conversion
An inorganic/organic core-shell TiO2 material and mesoporous TiO2 loaded with metals (Cu, Pt) were synthesized and employed as catalysts for the photocatalytic conversion of CO2 into fine chemicals, using an advanced photocatalytic reactor designed and fabricated in our lab. The experimental parameters were optimized and the tested material exhibited significant CO2 conversion rates, under both UV and Visible irradiation, rendering the whole procedure fully sustainable.
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- FP7-PEOPLE-2012-ITN, “DESTINY- Dye Sensitized solar cells with enhanced stability”, 468.337,76 €.
- ARISTEIA, GSRT, “AdMatDSC-Advanced Materials for DSCs of enhanced efficiency”, 352.000 €
- FP7-ENERGY-2011-1, “IOLICAP- Novel ionic liquid and supported ionic liquid solvents for reversible capture of CO2”, Project number: 283077, 2011-2014 (Coordination of the project: G. Romanos/NCSRD), 1.070 K€6.
- Thalis project “AOP-NanoMat: Development of Advanced Oxidation Processes (AOPs) with the use of nanomaterials and sunlight, for the removal of various organic toxic micropollutants, endocrine disrupters and cyanotoxins from natural waters and sewages”, (coordination of the project: Prof. T. Albanis/Univ of Ioannina). Budget for NCSR “Demokritos : 80.100 €
- Thalis project “NANOMESO: Materials of advanced nano-architecture at mesoscale for energy and environmental applications”, (coordination of the project: P. Pomonis /Univ of Ioannina). Budget for NCSR “Demokritos : 80.348 €
- Thalis project “NANOSOLCEL: Innovative materials for nanocrystalline solar cells”, (coordination of the project: Prof. P. Lianos /Univ of Patras. Budget for NCSR “Demokritos : 103.496 €
- ARISTEIA, GSRT, “SolMeD- Desalination by Solar Powered Membrane Distillation: Material and Process Optimization”, (coordination of the project: M. Mathioulakis/NCSRD).
- KRIPIS, GSRT, “Advanced materials and devices for energy collection and management”, (coordination of the project: D. Niarchos/NCSRD).
- Thalis project “Development of new material from rejected biomass for adsorption of hydrocarbons in marine environment”, (coordination of the project: Prof. D. Sideras/University of Piraeus).
Awards / Distinctions
- P. Falaras received the Alternative Water Resources Prize from PSIPW International Prize for Water (www.psipw.org), Riyadh, Saudi Arabia, 15 December 2014 (http://youtu.be/pPsHpAwwtVU and http://www.arabnews.com/news/644591).
- P. Falaras, T. Stergiopoulos and M. Konstantakou received the Theodoros Aretaios Award (Original Scientific Paper in Physical Sciences), from the Academy of Athens on December 19 2014, for their work: “Dye solar cells combining TiO2 surface-blocking organic sensitizer and solvent-free ionic liquid-based redox electrolyte”, Thomas Stergiopoulos, Maria Konstantakou and Polycarpos Falaras, RSC Adv. (2013), 3, 15014-15021.
- N. Moustakas received the ‘Green Talent 2014 Award: International Forum for High Potentials in Sustainable Development’ in the Competition organized by the German Federal Ministry of Education and Research (BMBF) (http://www.greentalents.de/).
- P. Falaras was elected Member of the Council of TEI of Western Greece.
- P. Falaras was nominated Member of TES/ESET in Physical Sciences.
- P. Falaras was nominated Member of the Scientific Committee of the National Documentation and Electronic Information.
- P. Falaras was nominated Member of the Scientific Committee of the AOPs PhD School http://www.aops-school.com/committee/
- T. Stergiopoulos continued his career in Oxford University (UK) on a MC IF grant.
- V. Likodimos was appointed Assistant Professor at the Department of Physics, National Technical of Athens, Greece.
- G. Vougioukalakis was appointed Lecturer at the Department of Chemistry, National Technical of Athens, Greece.
- Science Direct TOP25 Hottest Article (first ranked for all of 2013 and 2014) in Catalysis/Chemical Engineering for Elsevier Journals [Appl. Catal B: Environm., 125 (2012) 331– 349].
- Most Downloaded Paper (1st ranked) of JPCL for all 2014 [J.Phys. Chem. Lett. (2014) 5, 2543-2554].
- Most Downloaded Organic Electronics Articles for 2014 [Organic Electronics (2014) 15, 1347–1361].