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THE 8th INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ROCAM 2015

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S1Advanced Materials for solar energy conversion

Invited Papers


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LARGE-AREA MAGNETRON SPUTTERING OF SOLAR CELLS AND ELECTRODES FOR WATER

SPLITTING FOR OUR FUTURE RENEWABLE ENERGY SUPPLY

Klaus EllmerHelmholtz-Zentrum fr Materialien und Energie, dept. solar fuels, Hahn-Meitner-Platz 1, 14109 Berlin, Germany, e-

[email protected]

Magnetron sputtering, invented by the renowned plasma physicist Penning already in 1939, is today a widely usedlarge-area, plasma-assisted deposition method for many industrial applications like

architectural and low emissivity glass coatings, hard coatings, optical and protective films, magnetic layers for hard disk drives, transparent electrodes thin film solar cells, to name only a few.In this lecture the potential distribution and energetic species in a magnetron discharge are explained and related to

electronic properties of Al-doped zinc oxide, a transparent conductive oxide (TCO), used for instance in thin film solarcells.

The energies of the species contributing and assisting the film growth are significantly higher compared to thermal

or plasma-enhanced chemical vapour (PECVD) deposition processes. The sputtered species, forming the deposited film,exhibit energies in the range of some to tens of electron volts. Since in typical magnetron sputtering systems thedischarge voltages can reach hundreds of volts, some species, especially negative ions (O-, S-, F- etc.), can even reachenergies of hundreds of eV. This is one of the reasons, why magnetron sputtering is not yet used on an industrial scalefor the deposition of active semiconducting films, for instance in thin film solar cells.

By using energy-resolved mass spectrometry we have shown that the detrimental high-energy flux of negative ionsis strongly reduced when the discharge frequency is increased from d.c. up to 27 MHz. On the other hand, the often

beneficial low-energy ion flux that the positive ions provide is enhanced for r.f. discharges. Thus, these quantitative ionenergy and flux measurements explain the empirical fact, that for TCOs and other semiconductors often r.f. magnetronsputtering leads to better films.

This was demonstrated for ZnO:Al films, deposited as a function of the substrate temperature for 3 dischargefrequencies: d.c., 13.56 and 27.12 MHz.

The effects of the plasma excitation energy on the electronic properties of the active layers in thin film solar cells

and photoelectrodes are demonstrated for the materials Cu(In,Ga)Se2and BiVO4.

THE INFLUENCE OF VARYING GROWTH PARAMETERS ON THE QUALITY OF MULTI-

CRYSTALLINE SILICON GROWN BY A BRIDGMAN TECHNIQUE

Radu Andrei Negrila, Vasile Pupazan, Alexandra Popescu and Daniel VizmanPhysics Faculty, West University of Timisoara, Bd. V. Parvan 4, 300223 Timisoara, Romania, corresponding author:

[email protected]

In the race to improve the price of solar energy by lowering the costs for silicon solar panel production, one of theimportant production segments to be addressed are the purification and crystallization of photovoltaic grade silicon. Itstands for almost 1/3 of the total production cost. Currently, directionally solidified multi-crystalline silicon is

predominant in the market of photovoltaic silicon (2015: 60%) and is expected to stay so during the following decade.Because of its low costs and its similarities with directional solidification, Bridgman growth of small diameter (max.3cm) multi-crystalline silicon is a suitable technique for a fundamental study of the influence of growth parameters (likegrowth rate and process time, temperature gradients, crucible coating) on the interface shape, grains size and impuritydistribution and precipitation, which are important parameters for the photovoltaic applications. As silicon iscrystallized in non-reusable silica crucibles with anti-sticking silicon nitride coatings, experimental investigations have

been performed on new different crucible-coating combinations for the identification of cheaper and maybe evenreusable crucible materials. Even though an electronic grade quality (very high purity) Silicon feedstock was employeda large distribution of impurity precipitates (especially of SiC, which is highly undesirable because it induces damageduring wafering of silicon ingots) was found in most growth experiments. A very high neutral impurity (C and O)concentration has been found. These impurities have largely entered the molten silicon through diffusion into the liquid

phase, aided by convective transport. Therefore the impurity concentration in the melt is strongly related with the timeduration in which the silicon was in the molten phase, but also to the different coating materials that were employed.These observations are discussed in the interest of discerning the influence of the different growth conditions on theaccumulation and precipitation of impurities and crystalline structure. This understanding is a key aspect in improvingthe quality of the photovoltaic material by tailoring the different growth parameters.
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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TOWARDS HIGH EFFICIENCY STABLE ORGANIC PHOTOVOLTAICS

Elizabeth von Hauff

Department of Physics and Astronomy, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands

Organic semiconductors offer vast potential to realise low cost, large scale photovoltaic applications. Modification

to the chemical structure of the organic semiconductor allows for enormous flexibility to tune the opto-electronicresponse of the molecule. The development of new absorber materials has led to rapid increases in power conversionefficiency, and record efficiencies for organic solar cells have exceeded 10 %. This is generally considered a benchmarkvalue for the market entry of low cost photovoltaics. In addition to efficiency, the lifetime and reliability of a

photovoltaic technology is very critical for determining feasibility. Recent research efforts in the field have beenfocussed on understanding the fundamental mechanisms which lead to performance loss in organic photovoltaicdevices. The challenge is to identify and localise microscopic loss processes in such complex device architectures. Inthis talk I will discuss the opto-electronic properties of high performance organic solar cells. Frequency-resolvedtechniques such as intensity modulated photocurrent spectroscopy and impedance spectroscopy are very powerful forextracting highly detailed information related to electronic structure of materials and interfaces, as well as transport andtrapping phenomena which influence the current-voltage characteristic. This allows us to reconstruct the density ofelectronic states, and monitor how the transport properties of the devices change over time.

ORGANIC AND HYBRID BIOLOGIC/ORGANIC STRUCTURES FOR PHOTOVOLTAIC APPLICATIONS

tefan Antohe1,2

1University of Bucharest, Faculty of Physics, P.O.Box: MG-11, Bucharest-Magurele, 077125 ROMANIA, E-mail:[email protected], 2Academy of Romanian Scientists-Physics

In the last decades the second and third generations of photovoltaic cells based organic thin films have attracted agreat deal of interest among scientists involved in the research efforts to produce efficient and low-cost solar cells.More recently, the biological materials were tested successfully in electronic and optoelectronic applications. Amongthe organic semiconductors envisaged to be used in such structures, small molecules like metal-doped phthalocyanines(MePc, with Me=Cu, Mg, Zn, etc.) and polymers are the most studied, due to their peculiar optical properties. As

biologic semiconductor, the Chlorophyll-a is a potential candidate for photovoltaic structures. For these materials, theoptical absorption in the visible range of the solar spectrum is strong, but based on an excitonic mechanism. A typicalvalue for the diffusion length of the exciton in organic semiconductors is of 30-80 nm, while in order to achieve therequired efficiency in light absorption, the absorber layer has to be at least 100 nm thick. This inconvenient could beavoid, by the preparation of the multilayered structures containing different organic and biologic absorbers, or creatinga large number of Donor/Acceptor Interfaces, spread in the whole volume of the composite absorber, leading to so call,,Bulkheterojunctioncells.

In this work are summarized the electrical and photoelectrical properties of the photovoltaic cells based on theorganic (small molecules and polymers) and biologic thin films. In the case of second generation of photovoltaic cells,first the single-layer structures (ITO/CuPc/Al and ITO/TPyP/Al) were been prepared and characterized. The double-layer photovoltaic structures based on the p-n heterojunction present at the interface between two organic layers, like,ITO/CuPc/TPyP/Al and ITO/Chl a/TPyP/Al, exhibits stronger spectral sensitivity and better spectral matching to a solarspectrum than Schottky cells using either CuPc or TPyP layer, having a power conversion efficiency with about twoorders of magnitude, higher than those of single-layer structures. Three-layered organic solar cells with an interlayer ofco-deposited dyes of p-type CuPc and n-type TPyP, between the respective dye layers were also prepared andcharacterized, showing an increased power conversion efficiency, with respect of doublelayer structures.

In the case of third generation of solar cells, the polymeric photovoltaic cells were produced by spin-coatingtechnique. The structures based on the P3HT: PCBM (1:1) blend and the hybrid structures of Chl/:P3HT:PCBM(1:1)shows a promising photovoltaic response, with a power conversion efficiency increased of about two order of degree,with respect of those measured in the case of structures based on single P3HT and PCBM or Chl-a thin films. Differentdesign of structures were prepared and characterized trying permanently to improve the performances and the stabilityof the photovoltaic cells.

Keywords:organic thin films, chlorophyll-a, Bulkheterojunction photovoltaic cells
mailto:[email protected]:[email protected]:[email protected]


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TRENDS IN THE NEW GENERATION SOLAR CELLS RESEARCH

Mihaela GirtanLPHIAPhotonics Laboratory, LUNAM - Angers University, 2 Bd. Lavoisier, 49045, Angers, France,

[email protected]

Since the 50s when the concept of the first semiconducting photovoltaic cell was practically proved, differentmaterials and technologies were tested in order to increase the conversion efficiencies and to reduce the fabricationcosts. Today world records conversion efficiencies for single junctions solar cells without concentrators are of 28,8%for thin film GaAs[1], of 25% for single crystal monocrystalline Si [2], 21.7% for CIGS thin films [3], 19.3.% for

perovskites cells [4], 13.4% for amorphous silicon thin films solar cells [5], 11.9% for dye sensitized cells [6] and of11.1 % for organic solar cells [7].

For the industrial development of different technologies many aspects should be taken into account: i) theefficiency, ii) the materials cost and iii) the life time of materials and solar energy devices.

Due to the discrete band structure of semiconductors, only photons with energies equal or greater than the bandgapenergy (Eg) will be absorbed and contribute to the electrical photovoltaic solar cell output. Photons having higherenergies than Eg, even they are absorbed, their energies are underutilized due to the thermalization of charge carriers. Inorder to reduce these spectral losses and increase the energy conversion efficacy, many strategies were considered, suchas: multi-junction cells (multiple semiconductors stacked cells, intermediate band semiconductors solar cell, up and

down converters. Up and down converters are based on rare earth doped materials which may modify the photonsenergies in order to adapt them to the corresponding value of the band gap of the active material. Hence, the advantageof this concept is that one that it could be applied to all types of solar cells.

Another important aspect represent the solar cells cost. A lot of work was done for all kind of photovoltaics devicesin order to reduce the fabrication costs, by looking for less expensive materials for transparent electrodes and activelayers and also less expensive technologies such as: spray, ink jet or roll to roll deposition methods.

Finally, but not less important is the life duration of materials and devices involved in solar cells and solar cellspanels fabrication. Silicon has the advantage to be a very stable material, but recent studies shows that also someconducting polymers such as PEDOT-PSS, P3HT and PCDTBT usually used in the fabrication of organic solar cellsare enough stable too to be developed at industrial scale.

In this talk we present the state of art and the new trends in solar cells research.References[1] B.M. Kayes, L. Zhang, I.K. Ding, G.S. Higashi, Flexible Thin-Film Tandem Solar Cells With > 30%

Efficiency, Ieee J. Photovolt. 4 (2014) 729733. doi:10.1109/jphotov.2014.2299395.[2] K. Masuko, M. Shigematsu, T. Hashiguchi, D. Fujishima, M. Kai, N. Yoshimura, et al., Achievement of MoreThan 25% Conversion Efficiency With Crystalline Silicon Heterojunction Solar Cell, Ieee J. Photovolt. 4 (2014) 14331435. doi:10.1109/jphotov.2014.2352151.

[3] P. Jackson, D. Hariskos, R. Wuerz, O. Kiowski, A. Bauer, T.M. Friedlmeier, et al., Properties of Cu(In,Ga)Se2solar cells with new record efficiencies up to 21.7%, Phys. Status Solidi RRL Rapid Res. Lett. 9999 (2014) n/an/a.doi:10.1002/pssr.201409520.

[4] H.S. Jung, N.-G. Park, Perovskite solar cells: from materials to devices., Small Weinh. Bergstr. Ger. 11 (2015).doi:10.1002/smll.201402767.

[5] O. Isabella, A.H.M. Smets, M. Zeman, Thin-film silicon-based quadruple junction solar cells approaching 20%conversion efficiency, Sol. Energy Mater. Sol. Cells. 129 (2014) 8289. doi:10.1016/j.solmat.2014.03.021.

[6] M.K. Panda, K. Ladomenou, A.G. Coutsolelos, Porphyrins in bio-inspired transformations: Light-harvesting tosolar cell, Coord. Chem. Rev. 256 (2012) 26012627. doi:10.1016/j.ccr.2012.04.041.

[7] O. Adebanjo, P.P. Maharjan, P. Adhikary, M. Wang, S. Yang, Q. Qiao, Triple junction polymer solar cells,Energy Environ. Sci. 6 (2013) 31503170. doi:10.1039/c3ee42257g.


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SOLAR CELLS ON CELLULOSE PAPER TO BACK UP SMART PAPER ELECTRONICS

Rodrigo Martins, L. Pereira, A. Vicente, H. guas, D. Gaspar, T. Mateus, A. Arajo, Elvira FortunatoCENIMAT/I3N, Departamento de Cincia dos Materiais, Faculdade de Cincias e Tecnologia, FCT, Universidade

Nova de Lisboa and CEMOP-UNINOVA, 2829-516 Caparica, Portugal.

Nowadays there is a strong demand for smart packaging to provide comfort, welfare and security to owners, vendorsand consumers, by allowing them to know the contents and interact with the goods. This is of particular relevance forlow cost, fully disposable and recyclable products like identification tags, medical diagnostic tests and devices foranalysis and/or quality control in food and pharmaceutical industry1-3, most of them requiring continuous power whichcan be addressed by a combined use of a small disposable solid state battery 4, charged by a disposable solar cells5, ableto work under indoor lighting. Presently, the development of non-wafer-based photovoltaics allows supporting thin filmsolar cells on a wide variety of low-cost recyclable and flexible substrates such as paper; thereby extending PVsolutions to a broad range of consumer-oriented indoor disposable applications where autonomous energy harvesting istoday a bottleneck issue. Here, we show a proof-of-concept of the pioneering production of thin-film amorphous silicon(a-Si:H) photovoltaic cells with efficiencies of 4%5, by plasma enhanced chemical vapor deposition (PECVD), on

packaging cardboard (LPC)6commonly used in the food and beverage industry. Such accomplishment put us one stepcloser to this revolution, by providing a flexible, renewable and extremely cheap autonomous energy packaging system.Moreover, such Si thin films take advantage of their good performance at low-light levels, which also makes them

highly desirable for cheap mobile indoor applications. We also process solar cells on paper coated with a layer of ahydrophilic mesoporous (HM) material, where, as a proof f concept we produce solar cells with a 3.4% efficiency.The way how cells were produced, the existing challenges and the plethora of electronics 7-10 that they can serve will

be presented and discussed in this presentation.References[1] R. Martins, L. Pereira, E. Fortunato, SID 2014Frontline Technology: The Future Is Paper Based, p20-24Vol 52

(2014), pp. 50-55[2] R. Martins, I. Ferreira and E. Fortunato, Electronics with and on paper. Physica Status Solidi - RapidResearch

Letters, 5 (9) (2011), pp. 332-335.[3] D. Tobjork, R. & Osterbacka, Paper Electronics. Advanced Materials 23, (2011), pp.1935-1961.[4] I. Ferreira, B. Bras, J.I. Martins, N. Correia, P. Barquinha, E. Fortunato, R. Martins, Solid -state paper batteries

for controlling paper transistors. Electrochimica Acta 56 (2011) 10991105[5] A. Vicente, H. guas, T. Mateus, A. Arajo, A. Lyubchyk, S. Siitonen, E. Fortunato, R. Martins, Solar Cells for

Self-Sustainable intelligent Packaging, J. Materials Chemistry A, 2015, DOI 10.1039/C5TA01752A.[6] Stora Enso. http://www.storaenso.com. Accessed 15 November 2014.[7] Martins, R. F. P., Ahnood, A., Correia, N., Pereira, L., Barros, R., Barquinha, P., Costa, R., Ferreira, I. M.M.,

Nathan, A. & Fortunato, E. Recyclable, Flexible, Low-Power Oxide Electronics. Advanced Functional Materials 23,2153-2161, doi:10.1002/adfm.201202907 (2013).

[8] R. Martins, P. Barquinha, L. Pereira, N. Correia, G. Gonalves, I. Ferreira, E. Fortunato, Write -erase and readpaper memory transistor. Applied Physics Letters, 93 (2008) pp. 203501-203504

[9] E. Fortunato, N. Correia, P. Barquinha, L. Pereira, G. Gonalves, R. Martins, High -Performance FlexibleHybrid Field-Effect Transistors Based on Cellulose Fiber Paper. IEEE Electron Device Letters, 29, (9) (2008) pp. 988 -990.

[10] Pedro Barquinha, Rodrigo Martins, Luis Pereira, Elvira Fortunato, Transparent Semiconductors: FromMaterials to Devices. West Sussex: Wiley & Sons (March 2012), ISBN 9780470683736

BIOINTERFACES WITH BIO-INSPIRED ORGANIC SEMICONDUCTORS

Eric Daniel GowackiLinz Institute for Organic Solar Cells (LIOS), Physical Chemistry, Johannes Kepler University, Linz Austria; email:

[email protected]

We review recent work from our group as well as other researchers demonstrating the efficacy of using natural-origin materials in semiconductor-based devices for interfacing with biology. Many natural materials offer bothexcellent semiconducting properties, and importantly, electronic as well as ionic conductivity. Biochemical systems areionic, and not electronic, thus any attempts of active bioelectronics devices must involve ionic/electronic transducingelements. In particular, progress in the use of nanocrystalline and microcrystalline organic hydrogen-bonded pigmentswill be discussed. These materials have been ubiquitous throughout history and are widely produced today industriallyas colorants in everyday products as various as cosmetics and printing inks, and have numerous properties that makethem intrinsically biocompatible. The bioconjugation chemistry of these materials and subsequent deployment inelectronic devices requiring reliable and specific bio-sensing will be covered.


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VIS-ACTIVE PHOTOCATALYTIC TANDEM SYSTEMS- A FIRST STEP TOWARDS WATER RE-USE

Anca Duta*, Dana Perniu, Crisina Bogatu, Alexandru EnescaTransilvania University of Brasov, R&D Centre Renewable Energy systems and Recycling, Eroilor 29, 500036 Brasov,

Romania, *Corresponding author:[email protected]

Water is one of the most abundant natural resources; however, water that can be used with convenient costs in

industrial and day-to-day life processes is in much smaller amounts, continuously decreasing as result of the treatedwastewaters discharged in the environment with traces of recalcitrant or toxic pollutants. Cumulative, these pollutantsare slowly degrading the natural water quality, making the treatment processes more expensive. Thus, we are nowfacing a water stress. One path to reduce it is to treat wastewater at the quality required for re-use and advancedoxidation processes, based on heterogeneous photocatalysis are recognized as viable. To reduce the costs in the

photocatalytic processes requires the extended use of Vis- or solar radiation to activate the oxidation mechanism.Based on a synthetic review of the mostly investigated routs to obtain Vis-active photocatalysts, the paper proposes

a group of tandem composite systems with 3 and 4 components. The activation mechanisms is comparatively discussedfor systems containing SnO2, CuxS and TiO2or ZnO, deposited as thin films by Spray Pyrolysis.

The photocatalytic efficiency of the thin film tandems was tested on reference systems consisting of a dye(methylene blue) and a pesticide precursor (phenol) and the factors affecting mineralization are outlined. The stabilityof the best performing tandem is discussed based on the photo-corrosion resistance.

The results prove that in optimized photcatalytic systems, under optimized process parameters, the organic

pollutants in water can be mineralized at a level that allow the direct re-use of the treated water.


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Oral Presentations

CORRELATION OF DEFECT STATES WITH P3HT:PCBM SOLAR CELL ELECTRICAL PARAMETERS

Michal Kaiser1,2, Vojtech Ndady11Institute of Physics, Slovak Academy of Sciences; 2Faculty of Electrical Engineering and Information Technology,

Slovak University of Technology in Bratislava; e-mail:[email protected]

The understanding of degradation processes and related defect states represents important factor for further

improvement of organic solar cells (OSC). The charge capture and recombination at these states result in carriermobility decrease, photocurrent loss, and consequently, in the drop of power conversion efficiency. Most of previousstudies performed with various optical and electrical methods have focused on such a high degree of the organic filmdegradation which was far behind OSC functionality and could not be correlated with OSC electrical parameters.

Here we present experiments which correlate defect states in OSC active layer and the degradation of OSC electricalparameters. We investigated the defect states induced by ambient air, humid air, and UV/Vis irradiation. The purpose isto identify the impact of these degradation agents on particular photovoltaic process. In order to find this correlation weused charge deep-level transient spectroscopy (Q-DLTS) which was directly applied to OSC samples. The activationenergy, frequency factor, and the concentration of defect states were investigated with Q-DLTS via temperature andisothermal scans. The basic electrical parameters of OSC including photocurrent, ideality factor, reverse saturationcurrent, shunt and series resistances as well as the exciton generation rate and its dissociation probability weredetermined from dark and light I-V measurements.

We observed the formation of oxygen-related defect states with energy about 0.1 eV above HOMO of P3HT during

OSC degradation. Our preliminary results suggest that the oxygen-related defect states have a dominant impact onexciton recombination leading mainly to photocurrent loss. The correlation of these states with OSC electrical

parameters indicates two stages of OSC degradation. The obtained results are discussed and compared with otherrelevant published data.


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BIOLOGIC/POLYMERIC SEMICONDUCTING THIN FILMS BASED PHOTOVOLTAIC CELLS

S. Iftimie1, M.E. Barbinta-Patrascu1, A. Radu1, B. Bita1,2, N. Vasile1, N. Korganci1, L. Ion1 and S. Antohe1,31University of Bucharest, Faculty of Physics, 405 Atomistilor, P.O. Box: MG-11, 077125, Magurele, Ilfov, Romania,

2National Institute for Research and Development in MicrotechnologyIMT Bucharest, P.O. Box:38-160, 023573,Bucharest, Romania, 3Academy of Romanian Scientists, 54 Splaiul Independentei, 050094, Bucharest, Romania

Photovoltaic cells based on biologic (Chlorophyll-a, Chl-a) and polymeric (poly(3-hexylthiophene-2,5-diyl), P3HT)and ([6,6]-phenyl-C61 butyric acid methyl ester, PCBM) thin films were fabricated and characterized. Two types ofstructures were obtained, either a bi-layer Chl-a/P3HT:PCBM (1:1, wt. %) or a single layer Chl-a:P3HT:PCBM (10:1:1,wt. %) architecture. The spin-coating technique was used for the deposition of the biologic and polymeric thin films onthe ITO glasses, used as substrate and thermal vacuum evaporation technique was used to prepare the aluminum (Al)thin film as back contact . The optical and photovoltaic properties of the prepared photovoltaic cells, were analyzed andcompared with those for P3HT:PCBM (1:1, wt. %) structures. Similar values were registered for fill factor and opencircuit voltage, but the spectral response was enlarged for those cells containing Chl-a. For the moment, the short-circuitcurrent values for the non optimized cells Chl-a/P3HT:PCBM (1:1, wt.%) and Chl-a:P3HT:PCBM (10:1:1, wt.%) weresmaller than for P3HT:PCBM (1:1, wt.%) cells, but the future optimized structures (by a very good control of the filmthickness and design) will have improved performances.

Keywords:polymeric thin films, Chl-a, photovoltaic cells

TOWARDS OFFSETTING UP AN INTERMEDIATE BAND SOLAR CELL BASED ON TITANIUM OXIDES

SOL-GELS

S. Bechu1*, A. Goullet1, L. Cattin-Guenadez1, D. Duche2, J-J. Simon2, M. Girtan3, L. Brohan1, M. Richard-Plouet1

1. IMN-Universit de Nantes, Nantes, 2. IM2NP, Marseille, 3. LPHIA, Angers, * corresponding author :[email protected]

Third generation solar cells aims at increasing efficiency to overtake the 31% theoretical efficiency of simplejunction photovoltaic cells established by Shockley and Queisser [1] in 1961. According to Marti and Luque [2],intermediate band cell concept could increase the photocurrent via the absorption of sub-bandgap photons withoutdegrading the voltage.

In this perspective, we developed hybrid photosensitive sols-gels based on titanium clusters with specific optical andelectronic properties [3]. Once illuminated under UV light, an intermediate band appears in the band structure so theabsorption spreads over visible to near infrared due to reduction of Ti(IV) in Ti(III). Thanks to this absorption rangeincrease, these sols-gels can be used as active layers in solar cell.

In order to optimize light absorption properties of the sol-gel layer, shaping optimisation and optical propertiesstudies were carried out. Thin films were obtained with an accurate control over thickness in the range from 150 nm to10 m. Ellipsometry and XPS studies were respectively undertaken to determine optimal thickness and electronicstructure evolution under UV illumination.

This layer with original properties could be implemented as active layers in new hybrid solar cells.

[1] Shockley, W., Queisser, H.J., Journal of Applied Physics, 32, 510 (1961)[2] Luque, A., Marti, A., Physical Review Letters, 28, 78, (1997)[3] Cottineau T., Brohan L., Pregelj M., Cevc P., Richard-Plouet M., Aron D., Advanced Functional Materials, 18,

2602 (2008)


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EFFECT OF IONIZING RADIATIONS ON THE CdS/CdTe HETEROJUNCTIONS USED FOR SPACE

APPLICATIONS

A. Radu1, V. Ghenescu2, M.M. Gugiu3, N. Vasile1, N. Korganci1, S. Iftimie1, L. Ion1and S. Antohe1,41University of Bucharest, Faculty of Physics, MDEO R&D Center, 077125, Magurele-Ilfov, Romania, 2Institute of

Space Science, 077125, Magurele-Ilfov, Romania, 3Horia Hulubei National Institute for R&D in Physics and Nuclear

Engineering, Magurele-Ilfov, 077125, Romania,

4

Academy of Romanian Scientists, 050094, Bucharest, RomaniaCadmium sulfide (CdS)/ cadmium telluride (CdTe) heterojunction based photovoltaic cells were fabricated onto

optical glass substrates covered with a thin indium tin oxide (ITO) layer, in superstrate configuration. In order tominimize the induced deposition defects, the window layer, cadmium sulfide, was deposited by rf-magnetronsputtering; the substrate was purposely unheated. CdTe layers were deposited on top of cadmium sulfide by thermalvacuum evaporation (TVE). To complete the photovoltaic structure a copper:gold (Cu:Au) back electrode wasdeposited by TVE, too. With high absorption coefficients, suitable band gaps and reduced masses as thin films,cadmium sulfide and cadmium telluride are candidates for terrestrial and space applications. Our fabricated structureswere irradiated with protons and alpha particles with 500 keV energies and 1011 particles/cm2 fluencies, respectively.These values are similar with those hitting artificial satellites orbiting the Earth. Electrical and photo-electricalmeasurements were performed in dark and AM 1.5, at room temperature. Monte-Carlo numerical simulations showed adetailed image of interaction between our samples and protons and alpha particles. Determined external quantum

efficiencies values (EQE) decreased after irradiation with protons and alpha particles but the peaks attributed tofundamental absorption thresholds for CdS and CdTe kept their as grown positions in the case of irradiation withprotons and were slightly shifted in the case of irradiation with alpha particles. Parameters characterizing a photovoltaiccell, short-circuit current, open circuit voltage and fill factor, were determined and compared for as grown andirradiated PV cells.

Keywords:cadmium sulfide, cadmium telluride, ionizing radiations, protons, alpha particles

ON THE STRUCTURAL AND OPTICAL PROPERTIES OF HYBRID PEROVSKITE THIN FILMS

Aurelian Catalin Galca, Andrei Gabriel Tomulescu, and Ioana PintilieNational Institute of Materials Physics, Atomistilor 105 bis, 077125 Magurele, Ilfov, Romania, corresponding author:

[email protected]

Perovskite-based solar cells have been proposed as novel photovoltaic devices with relatively good conversionefficiency [1-3]. Most of the reported studies are focused only on presenting the solar cells parameters (e.g. quantumefficiency, spectral response, fill factor), while the pure optical and structural properties of each layer are roughly

presented and discussed.In this work we report the exhaustive optical and microstructural properties of thin films of the active hybrid

perovskite. The thin films are obtained by using a complex recipe which includes a special cleaning of the amorphoussilicon oxide substrates and a careful mixing and treatment of the precursors, and by using afterwards the spin-coatingtechnique.

The hybrid perovskite with the chemical formula CH3NH3PbI3-xClxresults from the combination of CH3NH3I andPbI2/PbCl2solutions. Depending on the preparation conditions the secondary phase of inorganic halide (PbI 2/PbCl2) ismore or less present.

The authors acknowledge funding from EEA Financial Mechanism Office through the project no 8SEE/30.06.2014:Perovskites for Photovoltaic Efficient Conversion Technology.

References1. M. M. Lee et al., Science338 (2012) 643.2. B. Conings et al., Adv. Mater.26 (2014) 2041.3. H. Zhou et al. , Science345 (2014) 542.


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EFFICIENT PEROVSKITE SOLAR CELLS PREPARED BY SOLUTION PROCESSED VIA TWO STEP

DEPOSITION

Viorica Stancu, Marian Sima, Cristina Besleaga, Andrei Tomulescu, Mariana Sima, George Stan, Lucian Pintilie, IoanaPintilie

National Institute of Materials Physics,105bis Atomistilor, 077125 Magurele, Ilfov, Romania,[email protected]

Perovskite solar cells are the newest technology of photovoltaic systems. They are attractive due to their properties:high conversion efficiency, offers significantly higher voltages and their fabrication techniques are simple. The essentialcomponent of these solar cells is a light absorbing semiconductor material with a perovskite polycrystalline structure,CH3NH3PbX3 (X= Cl, Br, I). In this work, we fabricate perovskite solar cells with high power conversion efficiency(average value efficience 16.6%) using a two step deposition process of CH 3NH3PbI3-xClx perovskite film. The

preparation process of the perovskite film was completed using a solvent annealing technique, where solvent vapor isintroduced during the crystallization of the perovskite film to increase the crystallinity and grain size. Our perovskitesolar cell structure contains a glass/FTO substrate covered with a compact layer of TiO 2semiconductor. Over that isdeposit a mesoporous scaffold from the same semiconductor which is in a close contact with a perovskite film.Perovskite film which can work effectively as both absorber and an electron transporter is covered with a Li doped spiroOMeTAD film (hole transporter). A metallic contact (Mo and Ag) is deposited on the spiro OMeTAD film.

INVESTIGATION OF NEW ABSORBERS MATERIALS FOR EFFICIENT PHOTOVOLTAIC SOLARCELLS

P. Wahnona, P. Palaciosa, E. Menendez-Proupinb, E. Castellanosa, Lucenac, JC ConesacaInstituto de Energa Solar, Universidad Politcnica de Madrid, Ciudad Universitaria, 28040 Madrid, Spain;

bDepartamento de Fsica, Facultad de Ciencias, Universidad de Chile, Santiago, Chile; cInstituto de Catlisis yPetroleoqumica, CSIC, 28049 Madrid, Spain;[email protected]

One of the challenges of materials science today is to find new technologies that will be able to make the most ofrenewable energies. An example of new proposals in this field is the intermediate-band (IB) materials, which promisehigher efficiencies in photovoltaic applications.

We present in this work several materials actively studied as good absorbers for photovoltaic applications. The firstalternative consists in the introduction of a properly chosen transition metal at high concentration in an octahedralsemiconductor which gives in-gap delocalized and partially occupied levels, required by the Intermediate Band concept.The new intermediate band allows the absorption of low energy photon increasing the photo -current but maintaining the

photo-voltage. We have verified with accurate density functional theory (DFT) calculations and beyond, thatsemiconductors as In2S3 and layered SnS2 can provide this situation when an octahedral cation in their structure is

partially substituted by an element such as vanadium. For layered semiconductors, the van der Waals cleavage plane(0001) is characterized by hexagonal arrays of close packed chalcogenide ions which are covalently bound within X-M-X sandwiches. These materials are ideal substrates to study fundamental aspects of the metal/semiconductor interaction.

Experimental work made via wet chemistry methods verifies that new absorption features appear in the opticalabsorption spectrum which matches the predicted DFT-based theoretical absorption results. On the other hand, a

photocatalytic process (photooxidation of an organic compound in an aqueous suspension irradiated with wavelength-selected light) is used to experimentally assess, even on polycrystalline powder materials, the ability of subbandgap

photons to produce electron-hole pairs that can be extracted at the materials interface with scarce efficiency degradationby recombination effects. The spectral responses show that these materials have the appropriate characteristics forbuilding photovoltaic devices of boosted efficiency using the whole range of the visible light spectrum.

Nowadays other actively studied as novel photovoltaic material is the methyl-ammonium lead iodide perovskite(CH3NH3PbI3). We have computed its electronic structure and relevant properties of the othorhombic phase withaccurate DFT. The crystal structure, optimized using a van der Waals functional, reproduces closely the unit cellvolume. By combining spin-orbit effects, with hybrid functionals the experimental bandgap is also reproduced. Thecomputed binding energy of the unrelaxed exciton agrees with recently reported experimental data, and the valuesfound imply an easy exciton dissociation at room temperature. Fast dynamics and large diffusion lengths of the currentcarriers are key for the high photovoltaic efficiencies shown by these materials.
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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STRUCTURAL, MORPHOLOGICAL AND OPTICAL PROPERTIES OF RF-SPUTTERED CdS THIN

FILMS FOR PHOTOVOLTAIC APPLICATIONS

Ovidiu Toma, Sorina Iftimie, Lucian Ion, Stefan Antohe*University of Bucharest, Faculty of Physics, 405 Atomistilor Street, PO Box MG-11, 077125, Magurele-Ilfov,Romania, Presenting author:[email protected], *Corresponding author:[email protected]

Cadmium sulfide (CdS) nanocrystalline semiconductor thin films of different thickness were deposited using thetechnique of magnetron sputtering in radio-frequency plasma (RF MS). As cathodes high purity solid CdS targetswere used while optical glasses were employed as anode-substrates (the substrates were maintained at roomtemperatures). Optical, structural and morphological characterizations were carried out for the prepared CdS thin films.For the characterization of the optical properties of the CdS thin films spectroscopic ellipsometry (SE) was used in therange of 250 nm to 1700 nm. Optical constants (refractive indices, extinction coefficients, optical band gaps, etc.), aswell as film thicknesses and surface rugosities were measured by spectroscopic ellipsometry. This optical method wascombined with optical spectrophotometry (absorption spectra, transmission spectra, reflection spectra) in UV VIS

NIR for a better verification of the results. Structural investigations were carried out by X-Ray diffraction (XRD)technique, while morphological characterizations were performed using atomic force microscopy (AFM).


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Poster Presentations

OXIDE LAYERS CHARACTERIZATION IN GaSb TECHNOLOGY FOR PHOTOSENSITIVE

STRUCTURES

C. Cotirlan-Simioniuc1, C. Logofatu1, R.V. Ghita1, F. Frumosu1, M. Rusu21National Institute of Materials Physics, P.O.Box MG-7, 077125 Magurele, Ilfov, ROMANIA, E-mail:[email protected]

2National Institute for Optoelectronics-INOE 2000

GaSb-based semiconductor alloys have potential in cutting-edge applications for mid-infrared optoelectronics (Eg~

0.73 eV at 273 K) and thermophotovoltaics. It is stated [1] that the performance and reliability of GaSb devices largelydepend on surface preparation techniques (e.g. n-GaSb (100)) and requires a significant reduction of high levels ofreverse current and surface instabilities. GaSb surface is much more reactive than that of GaAs or InP and quicklyoxidizes under atmospheric conditions [2]. This work presents an XPS (X-ray Photoelectron Spectroscopy) of the nativeoxides on n-GaSb (Te doped ) where the irreversible nature of the reaction is related to the fact that the oxygen atomsare involved in chemical bonds. The evolution of Ga2O3 and Sb2O3 with temperature is presented in high vacuumheating. Low temperature action can produce on GaSb a non-equilibrium Ga2O3-Sb2O3 surface oxide layer in wetthermal oxidation process putted into evidence by XPS analysis. There are discussed the evolution of Sb2O3 and Ga2O3in four oxidation processes, namely: dry thermal oxidation in furnace (p=1 atm, T (150-200)0C ); wet thermal oxidation(water vapors T~(90-100)0C, N2flux ); dry thermal oxidation at low temperatures (T~550C ) and anodic oxidation. Thequality of surface oxide was also examined by Spectroscopic Ellipsometry technique. Due to the fact that the only stable

phases that can exist in thermodynamic equilibrium with GaSb are Ga2O3and elementary Sb, the problem of developinga stable oxide layer on GaSb surface to be used further for device processing is vital in GaSb technology. This work is

devoted to the study of a viable route in the technology of a Schottky photosensitive device on n-GaSb (100).References

[1] M.Perotin et al, Journal of Electronic Materials, Vol.23, No.1, pp.7-12 (1994).[2] E Papis-Polakowska , Electron Technology-Internet Journal 37/38, 4, pp.1-34 (2005/2006).

Acknowledgements:The financial and encouragement support provided by the Ministry of Educations of the Romania-UEFISCDI,

Project No. 68/2014


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NICKEL OXIDE COMPOSITES AS HOLE TRANSPORT LAYER IN POLYMER PHOTOVOLTAIC CELLS

AND AS ELECTRODE MATERIAL FOR SUPERCAPACITORS

Diana M. Brusa, Luis Echegoyenb, Marta E. Plonska-Brzezinska*aaInstitute of Chemistry, University of Bialystok, Hurtowa 1, 15-399 Bialystok, Poland. e-mail:[email protected],

bDepartment of Chemistry, University of Texas at El Paso, 500 W. University Ave., El Paso, TX 79968, USA.

The main subject of this work was synthesis of Carbon Nano-Onions (CNOs) and NiO composites which wereprepared by loading of Ni(OH)2 in different mass ratio on the carbon structures in the presence of 4-DMAP ((4-dimethylamino)pyridine), followed by calcination to obtain CNO/NiO. CNOs consist of 6-8 carbon shells (5-6 nm indiameter) and they can be also referred as multi-shelled fullerenes. The interest in carbon nano-onions is driven by theirunusual physico-chemical properties as well as by promising applications in electronics, optics, biosensors, and inenergy conversion and storage. CNOs/NiO were characterized by TEM, SEM, XRD, TGA-DTG-DTA, AFM, Raman,FT-IR spectroscopy, and the cyclic voltammetric and impedimetric measurements.

Carbon-based composites are currently being investigated as supercapacitor electrodes because of the synergisticproperties arising from the carbon materials (high power density) and from the pseudocapacitive nanomaterials (highenergy density). Therefore, NiO/4-DMAP could act as an efficient hole-transport layer (HTL) in polymer solar cells(PSCs) which are very promising organic-based devices for low-cost solar energy conversion. Nevertheless, one of thegreatest drawback of PSCs is their poor stability in ambient conditions. One of well-known HTL is PEDOT:PSS that is

strongly acidic in nature and lead degradation of the devices and limit their life. Therefore, the alternative is asubstitution of PEDOT:PSS by NiO. The hybrid material characterizes excellent stability, charge transport properties,charge selectivity and hole collection in PSCs.

We gratefully acknowledge the financial support of the National Science Centre, Poland, grant:

#2012/05/E/ST5/03800 to M.E.P.-B. L.E. thanks the Robert A. Welch Foundation for an endowed chair, grant #AH-

0033 and the US NSF, grants: CHE-1110967 and CHE-1124075.

HYBRID PEROVSKITE SOLAR CELLS: AGING EFFECTS AND RELIABILITY

C. Besleaga1, V. Stancu1, A.G. Tomulescu1, M. Sima1, L.M. Trinca1, G.E. Stan1, A.C. Galca1, L. Pintilie1, I. Pintilie1,A. Radu2, S. Iftimie2, L. Ion2, S. Antohe2, A. Nemnes2, C. Goehry3and A. Manolescu3

1National Institute of Materials Physics, Atomistilor 105 bis, 077125 Magurele, Ilfov, Romania, 2Faculty of Physics,University of Bucharest, Atomistilor 405, 077125 Magurele, Ilfov, Romania, 3School of Science and Engineering,

Reykjavik University, Menntavegur 1, IS-101 Reykjavik, Iceland

Perovskite-based solar cells have attracted the interest of the photovoltaics community due to their low fabricationcosts and very good conversion. Up to now, external efficiencies measured on this type of structures surpass 10% [1,2]with a best of 19% reported by Zhou etal.in 2014 [3]. In this work we report studies on high-performance solar cells

based on CH3NH3PbI3-xClxwith PCEs up to 16% on fresh devices. The hybrid perovskite thin film is obtained by spincoating, as well as the anatase (TiO2) and the spiro-OMeTAD, which play the roles of the blocking layer and the holetransport material (HTM), respectively. Degradation in time of the prepared devices was observed. The source of thisinstability is still under debate, being frequently suggested in literature that the aging of spiro-OMeTAD layer degradesthe cell and its efficiency [4]. The stability in time of the obtained photovoltaic devices, with and without spiro-OMeTAD, was assessed and discussed, in the search for performance enhancement paths. The effect of the HTM on theefficiency was also evaluated with numerical simulations. The research leading to these results has received fundingfrom EEA Financial Mecanism 2009 - 2014 under the project contract no 8SEE/30.06.2014.

References1. M. M. Lee et al., Science338 (2012) 643.2. B. Conings et al., Adv. Mater.26 (2014) 2041.3. H. Zhou et al. , Science345 (2014) 542.4. Anyi Mei et al.,Science345 (2014) 295-298.


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ZnO-BASED CONDUCTIVE OXIDE THIN FILMS AS TRANSPARENT CONTACT FOR PHOTOVOLTAIC

CELLS

L.M. Trinca1,2, A.C. Galca1, C. Besleaga1, A.G. Boni1, V. Stancu1, A.G. Tomulescu1, M. Sima1, L. Pintilie1, I. Pintilie11National Institute of Materials Physics, Atomistilor 105 bis, Magurele, Ilfov, Romania,2Faculty of Physics, University

of Bucharest, Atomistilor 405, Magurele, Ilfov, Romania, Contact author:[email protected]

ITO (Sn:In2O3) and FTO (F:SnO2) are the most common conductive oxides (TCOs) used as electrodes forphotovoltaic cells. Due to their high price, researchers are looking forward to replace them with abundant and lowproduction cost materials that pose both good transparency and conductivity. Al:ZnO (AZO) is given as an alternative,having resistivities as low as those of ITO (~10-4 cm) and also being highly transparent in visible spectrum.

In this work, AZO thin films were deposited on different substrates (glass, single crystal ZnO, polymer foil, singlecrystal SrTiO3). The optical and electrical properties of the films were correlated with the structural properties, with thenature of the substrate and with the deposition parameters.

The optimized AZO thin film was used as bottom electrode of hybrid perovskite solar cells. The photovoltaicresponse (external efficiency) was compared with the one of FTO - solar cell, fabricated in identical conditions.

The research leading to these results has received funding from EEA Financial Mecanism 2009 - 2014 under theproject contract no 8SEE/30.06.2014

Liliana M. Trinca acknowledge to the strategic grant POSDRU/159/1.5/S/137750.

NEW CHALCOGENIDE MATERIAL FOR PHOTOVOLTAIC CELLS

Z.S.ELMandouh and H.A.ELMeleegiNational Research Centre,EL-Tahrir St., Dokki,Cairo, Egypt, Affiliation ID: 60014618

Solar cell has been prepared from PbxIn25-xSe75 thin films by Pulsed Laser Deposition method. Pb0.01In0.24Se75and Pb0.03In0.22Se75 was confirmed to be p-and n- types respectively using Seebeck experiment as a thermoelectriceffect property proof of the thin film alloys under investigation. The disordered structure of such specimens wereconfirmed by diffraction electron microscope mode of JEM-1230 TEM. Current- voltage characteristics wheremeasured under illumination and in dark using KEITHLEY 6517A and, VIRTINS MULTI-INSTRUMENTS,oscilloscope and signal generator system. Short circuit current and open-circuit voltage was measured to deduce theFill-Factor as a property of such cell. The photoelectric Efficiency assured the participation probability for suchmaterials as a good candidate for solar cells.

MAPLE OBTAINED METAL PHTHALOCYANINES THIN FILMS ON FLEXIBLE SUBSTRATES

M. Socol1, N. Preda1, O. Rasoga1, C. Breazu1,2, F. Stanculescu2, G. Socol3, F. Gherendi3, M Girtan41National Institute of Material Physics,105 bis Atomistilor Street, 077125, Bucharest-Magurele, Romania,

2University

of Bucharest, Faculty of Physics, 405 Atomistilor Street, 077125, Bucharest-Magurele, Romania, 3National Institute forLasers, Plasma and Radiation Physics, 409 Atomistilor Street, 077125, Bucharest-Magurele, Romania, 4Laboratoire de

Photonique d'Angers, Universit dAngers, 2, Bd. Lavoisier, 49045, Angers, France ,[email protected]

Organic heterostructures based on metal (Zn and Mg) phthalocyanes (p types semiconductors) and 5,10,15,20-tetra(4-pyrydil)21H,23H-porphyne (n type semiconductor) were prepare by Matrix-Assisted Pulsed Laser Evaporation(MAPLE) tehnique on ITO flexible substrates. Structural, morphological, and optical properties of the bilayer and bulkheterojunctions were investigated by UV-VIS, Photoluminescence (PL) and FTIR spectroscopy as well as Atomic ForceMicroscopy (AFM) and Scanning Electron Microscopy (SEM). The layers preserved the properties of the initialmaterials and exhibited a large absorption in the visible range of the solar spectrum. The morphology was characteristicto the MAPLE organic films with large grains. I-V characteristics of (Al/ZnPc(MgPc)/TPyP/ITO andAl/ZnPc(MgPc):TPyP/ITO) structures were recorded in dark and under the illumination with an solar simulator(AM1.5). In the bulk heterojunctions, the current value were found to be improved (at least one order of magnitude)compared to the value obtained in the bilayer heterojunction in the both case of the structures made with ZnPc or MgPc.


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EFFICIENCY ENHANCEMENT OF DSSC USING PLASMONIC NANOPARTICLES

Mohammed S. Rasheeda, A. K. Alib, Mihaela Girtana, Khaleel I. Hassoonba POMA Lab., FRE CNRS 2988, Angers University, 2, Bd. Lavoisier, 49045, Angers, France, b Department of Applied

Sciences, University of Technology, Baghdad, Iraq, E-mail address:[email protected]

In this work, Au nanoparticles (NPs) were prepared by pulsed laser ablation in liquid (PLAL) technique using Nd-Yag laser with three different energies per pulse (600, 700, and 800 mJ). The gold NPs have been added to Ru baseddye (N719) in order to form a plasmonic dye. After the adding of Au NPs colloidal to N719, the absorbance of the

plasmonic dye has increased significantly compared with the pure dye as revealed by UV-VIS spectroscopic analysis inthe figure below. In order to prepare the photo-electrode of the dye sensitized solar cell (DSSC), titanium dioxide filmof thickness about 10 m was deposited on a FTO glass and then immersed in the plasmonic dyes for 30 min. The TiO2coatings were sintered in air at 500 C for 30 min. The XRD analysis for the sintered TiO2pastes showed the usual

peaks observed in TiO2powders. However, the spectral Responsivity calculations demonstrated enhance photocurrentin the range from 500-580 nm. IV characteristics of the DSSC under AM1 illumination showed enhanced Isc and Voc

by 19 % and 17% respectively.

References[1] Guowei Yang, Laser Ablation in Liquids: Principles and Applications in the Preparation of Nanomaterials, 2012

Pan Stanford Publishing Pte. Ltd.[2] M. D. Brown, T. Suteewong, R. Kumar, V. DInnocenzo, A. Petrozza, M. M. Lee, U. Wiesner, and H. J.

Snaith, Plasmonic Dye-Sensitized Solar Cells Using Core-Shell Metal-Insulator Nanoparticles. Nano Lett. 2011, 11,438445.

STRUCTURAL AND OPTICAL PROPERTIES OF RF SPUTTERED ZnO:Ga THIN FILMS

Fawzy. A. Mahmoud1,2*, Mohammed Rasheed3, Ahmed F. Mabied1, M.Girtan31Solid State Physics Dept., National Research Centre, P.O. 12311, Dokki, Giza, Egypt, 2Renewable Energy Group,Center of Excellence for Advanced Sciences, National Research Centre, P.O.12311, Dokki, Giza, Egypt, 3Angers

University, Photonics Laboratory, Angers, France

ZnO:Ga films were deposited on quartz substrates by RF magnetron sputtering using ZnO:Ga target. Four types ofsamples were prepared with various RF magnetron powers of 100, 150, 200 and 300Watt. The properties of these filmswere investigated using X-ray diffraction (XRD), optical transmittance and reflectance, FESEM, and spectroscopicellipsometry in the spectral region of 200 to 1200 nm. The structural and optical properties of the prepared films wereaffected by RF power. Relationships between structure of sputtered ZnO:Ga films and the optical constants wereinvestigated with varying RF power. The refractive and extinction coefficients were calculated by ellipsometry and thedata were correlated with the spectrophotometry measurements. Also the optical band gap was calculated from both

spectrophotometry and ellipsometry measurements, and very good correlations were founded.


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NORMAL AND INVERTED ORGANIC SOLAR CELLS BASED ON SMALL MOLECULE COMPOUNDS

M. Socol1, O. Rasoga1, C. Breazu1, 2, N. Preda1, F. Stanculescu2, A. Stanculescu1, G. Socol3, M Girtan41National Institute of Material Physics, 105 bis Atomistilor Street, 077125, Bucharest-Magurele, Romania,

2University

of Bucharest, Faculty of Physics, 405 Atomistilor Street, 077125, Bucharest-Magurele, Romania, 3National Institute forLasers, Plasma and Radiation Physics, 409 Atomistilor Street, 077125, Bucharest-Magurele, Romania, 4Laboratoire de

Photonique d'Angers, Universit dAngers, 2, Bd. Lavoisier, 49045, Angers, France,[email protected] [email protected]

In order to improve the electrical properties of the normal and inverted solar cell structures based on a zincphthalocyanine (ZnPc) and an 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) donor, respectively acceptorlayer, we study the effect of a fullerene aditional layer inserted between them. Indium tin oxide (ITO) was used astransparent conductive electrod coated with a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)layer in order to increase the charge conduction. The final structures are: glass/ITO/PEDOT:PSS/ZnPc/fullerene/NTCDA/Al and: glass/Al/NTCDA/fullerene/ZnPc/PEDOT:PSS/ITO for the inverted one. The metods usedfor the realization of the organic thin film structures were thermal vacuum evaporation for the small moleculecompounds and spin-coating for fullerene and PEDOT-PSS layers. Because a determinant role in the electrical

properties is played by the morphology of the layers, atomic force microscopy (AFM) and scanning electronmicroscopy (SEM) were used to investigate the surface of the thin films. Optical properties of the coatings have been

investigated by UV-VIS, photoluminescence (PL) and FTIR spectroscopy. I-V characteristics of the realized structureswere recorded in dark and under the illumination with a solar simulator (AM1.5). An improvment in the electrical

properties was observed for the inverted structures.

STRUCTURAL PROPERTIES OF CIGS THIN FILMS DEPOSITED BY MAGNETRON SPUTTERING

TECHNIQUE

P. Prepelitaa,1, V. Craciuna, M. Filipescua, I. Stavaracheb, D. Craciuna, F. Garoia, G. Sbarceac, A. VladaaNational Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, PO Box MG-36, 077125 Magurele,

Ilfov, Romania (1Married as Garoi), bNational Institute of Materials Physics, Magurele 077125, Romania, cNationalInstitute for R & D in Electrical Engineering ICPE-CA, Splaiul Unirii Street, Nr. 313, District 3, 030138, Bucharest

Romania

Copper indium gallium selenide (CIGS) thin films with various thicknesses (750 1200 nm) were deposited by RFmagnetron sputtering method. To simplify this procedure for deposition of chalcopyrite-type thin films, only a singleCIGS sintered target was used.

Deposition conditions for this study were: Ar pressure p= 4 10-44.3 10-4Torr, deposition rate rd= 1.6 1.7/s, 100 mm diameter target (CIGS circular disk of 99.99% purity).

The CIGS layer deposited on Mo coated glass substrate, with a thickness of 500 nm. Next, a CdS layer of 60 nmwas deposited by thermal vacuum evaporation technique. The top transparent contact electrode, ITO, was subsequentlydeposited by RF magnetron sputtering method. Atomic force microscopy (AFM) and scanning electron microscopy(SEM) investigations showed that the surface morphology changes depending on the deposition techniques and it isinfluenced by the increase in thicknesses of the layers..

Profilometry measurements showed evidence of changes in the step of the deposited layers, due to the interdiffusionfrom the level of each deposited layer or that will be deposited. From X-ray diffraction (XRD) measurements it was

found that all films were polycrystalline. CIGS films have a tetragonal structure with (112) plane parallel with thesurface of the substrate, and the grain size is influenced by thickness. The influence of thickness on the sampleselectrical and optical properties was also studied by quantum efficiency measurements.
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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DEGRADATION CHARACTERISTICS OF ZnO:B TREATED H/Ar FOR THIN FILM SOLAR CELL BY

DAMP HEAT

1,3Jae-Seong Jeong, 2Chang-Keun Park, 2Heon-Do Kim, and 3Joongho ChoiComponents and Materials Research Center, Korea Electronics Technology Institute (KETI), 1,3Robust Components and

System Research Center, Korea Electronics Technology Institute (KETI), 2 Advanced process development group,

Jusung Engineering Co. Ltd.,

3

Department of Electrical and Computer Engineering, University of Seoul,The TCO(transparent conducting oxide) thin film is an important layer which influence on Rs (series resistance) of

a-Si:H PV(photovoltaic) modules. ZnO thin film for TCO is known that it is weak to damp heat (85C, 85%RH) stress.Therefore robust design of ZnO is need to avoid degradation from moisture. ZnO:B thin film growth by MOCVD wasused for TCO. This study was investigated degradation reaction of ZnO:B thin film treated H/Ar due to the moisture.Electrical characteristics of ZnO:B thin film treated H/Ar were analyzed. The physical/chemical properties of ZnO:Bthin film treated H/Ar were analyzed by XPS and SIMS.

NEW HYBRID MATERIAL WITH APPLICATIONS IN THE SOLAR ENERGY AREA

Nandina Vlatanescu2, Daniel Berki2, Adina Segneanu1, Daniel Damian1,2and Ioan Grozescu1,2

National Institute of R&D for Electrochemistry and Condensed Matter INCEMC Timisoara University PolitehnicaTimisoara

Current global energy consumption is about 15 TW/year, and over two thirds of it is obtained from fossil fuels. Theenergy that arrives on the Earth in an hour from the Sun can provide global annual consumption. It is estimated thatfrom more than 105TW of sunlight hitting the earth, up to 600 TW is technically feasible to be used. Solar energy may

be harvested through its conversion to heat (solar- thermal), electrons (photovoltaic), or chemicals (solar-fuels). Theformer is perhaps the most straightforward, with installations ranging in scale from 1kW household water heaters to 50MW power plants located in areas of high solar insolation. Common approaches to solar fuels include the

photoelectrochemical splitting of water to produce H2and the reduction of CO2into liquid fuels such as methanol. Solarfuels remains the least developed strategy to harness solar energy, and is currently the focus of renewed efforts at the

basic research level.The paper investigates the synthesis of a new organic-inorganic hybrid material for application in solar energy

area. This new material comprises from an organic phosphorus derivate and Zn, Mg and P oxide type composite.Complete morpho-structural characterisation of this material was performed using XRD, SEM-EDAX, FT-IR andUV-Vis spectroscopy.

TIO2PHOTOCATALYTIC INKS FOR COLD SPRAYING DEPOSITION OF THIN FILMS

Panait Ramona, Nicoara Lavinia, Cristina Bogatu, Dana Perniu, Anca Duta*Transilvania University of Brasov, The Center Renewable Energy Systems and Recycling, Corresponding author:

[email protected]

Titania nanoparticles are widely investigated considering their applications: from photocatalysis (advancedwastewaters treatment, air purification), to solar cells, sensors, self-cleaning surfaces, paints, ceramic and coating etc.

Photocatalytic inks represent viable and cost effective solution if special applications like flexible substrates for solarcells, or self-cleaning fabrics based on photocatalysis are targeted. Due to the nanoparticles spontaneous agglomerationand sedimentation tendency in the continuous medium, ink stability remains the major problem that can limit theapplications.

In this study, Degussa P25 nanoparticles were dispersed under ultrasonication, in water or water-alcohol media toobtain stable dispersions. UV-Vis transmittance spectra were used to evaluate the dispersions stability.

To balance the van der Waals attractions and prevent the nanoparticles agglomeration, electrostatic repulsions canbe generated by using different stabilizers: surfactants (cationic-DTAB, HTAB, anionic-SDS, non-ionic-PEG),polymers (polyvinylpyrrolidone) and capping agents (TODA). The formation and changes in the particles double layerand the interactions developed at the particles/stabilizers/solvent interface were discussed considering the values of PZCand dispersion pH, concentration and ionic strength. Based on these, stabilization mechanisms were proposed.

The photocatalytic activity of the stabilized dispersions was tested on thin films obtained by cold sprayingdeposition. Methylene blue was used as test solution. Correlations between the film stability- photocatalytic properties

were developed and discussed in direct relation with the dispersions composition, but also considering the interactionsbetween the dispersions components and dispersionsubstrate.


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SYNTHESIS AND CHARACTERISATION OF ANTIMONY SULPHIDE (Sb2S3) THIN FILMS

P.A. Nwofe, and N.E. IdenyiDivision of Materials Science and Renewable Energy, Department of Industrial Physics, Ebonyi State University,

Abakaliki, P.M.B 053, Ebonyi State, Nigeria, E-mail:[email protected](P.A. Nwofe),[email protected](N.E. Idenyi)

Thin films of antimony sulphide were successfully grown using the solution growth technique and the effect of pHon the properties of the films was investigated. The pH range was varied between 4.2 - 8.5 and other depositionvariables were kept constant. The films were characterised using X-ray diffractometry (XRD) to investigate thestructural properties, Scanning electron microscopy (SEM) to study the morphological properties, RutherfordBackscattering (RBS) techniques for the compositional analysis, and optical spectroscopy to investigate thetransmittance, absorbance and reflectance versus wavelength measurements. The results show that films withthicknesses 500 nm were obtained at pH range of 4.2 - 6.0. Loss of stoichiometry was observed more in the alkalinerange. The results of the optical analysis indicate that the films had direct energy band gap with optical absorptioncoefficient () > 10

4 cm-1. The refractive index was typically 2.5, decreasing with increasingphoton energies. Thevalues of the extinction coefficient and the optical density are typically less than unity. The high optical absorptioncoefficient and direct energy bandgap obtained in the study, suggests possible use of the films as absorber layers in thinfilm photovoltaic (PV) solar cell devices.

GROWTH AND CHARACTERISATION OF DOPED NANOCRYSTALLINE ANTIMONY SULPHIDE

(Sb2S3) THIN FILMS

P.A. NwofeDivision of Materials Science and Renewable Energy, Department of Industrial Physics, Ebonyi State University,

Abakaliki, P.M.B 053, Ebonyi State, Nigeria, E-mail:[email protected]

In this study, the influence of zinc (Zn) and copper (Cu) impurities on the properties of antimony sulphide (Sb2S3)thin films grown using the solution growth technique is reported. The films were deposited at room temperature of28C, a deposition time of 4 h, and an initial pH of 4.80. The films were then doped with equal concentrations of therespective impurities and then annealed at annealing temperature of 300 C. The films were characterised using X-raydiffractometry (XRD) to investigate the structural properties, Scanning electron microscopy (SEM) to study themorphological properties, Rutherford Backscattering (RBS) techniques for the compositional analysis, and opticalspectroscopy to investigate the transmittance, absorbance and reflectance versus wavelength measurements. The resultsindicate that the film thickness was typically 600 nm, with an increase in the film thicknesses of the doped layerscompared to the as-deposited films. Information extracted from the XRD studies were used to deduce the crystallitessize, strain, number of crystallites, and the dislocation density. The transmittances of the doped layers were found to bereduced compared to the un-doped case. The results of the optical analysis show that the films had direct energy bandgap with optical absorption coefficient () > 104 cm -1 in both the doped and un-doped layers. The refractive index wastypically 3.0, with higher values obtained from the doped layers.

SOLAR-THERMAL COATINGS FOR NOVEL FLAT PLATE SOLAR THERMAL COLLECTORS

Lavinia Nicoara, Anca Duta*, Dana Perniu, Ramona Panait

Transilvania University of Brasov, R&D Centre Renewable Energy systems and Recycling, Eroilor 29, 500036 Brasov,Romania, *Corresponding author:[email protected]

The extended use of renewable energy systems is one of the main path for implementing sustainable development atcommunities level. Besides efficiency, the renewables integrated in communities, in/near the buildings have to gainarchitectural acceptance. Solar-thermal collectors represent one of the most common solution, already implemented inthe built environment, on rooftops or terraces. However, solar-thermal facades are seldom, especially because of thecommon colours of the flat plate solar-thermal collectors (black or dark blue).

The paper discusses the paths to increase the architectural acceptance of the flat plate solar thermal collectors, andproposes a range of composite nanostructures with various colours (red, green, orange) obtained using alumina matrixand inorganic oxides (pigments) with controlled morphology. The optical performances are discussed in terms of vis-absorptance and thermal emittance and show that spectral selective solar-thermal coatings with spectral selectivity S>9(market acceptable) can be obtained through wet chemical routes (sol-gel or chemical bath deposition). The addition of

Au-nanoparticles in very low concentrations is also discussed, in terms of materials control (nucleation) and output(colour, spectral selectivity). Optimised coatings are presented and the scaled-up flat plate solar-thermal demonstrator isdescribed.
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COMPARISON OF THE QUALITY OF PHENYL (3-HEXYTHIOPHENE) (P3HT) BLEND WITH

DIFFERENT ACCEPTOR ORGANIC MOLECULES HETEROJUNCTION ORGANIC SOLAR CELLS

Zainab Alhashim, Iulia Salaoru and Shashi PaulEmerging Technologies Research Centre, De Montfort University, Hawthorn Building Leicester LE1 9BH, UK

Among the renewable energy technologies, solar cells are one of the fastest growing technologies. Traditional ways

of harvesting this energy from the sun is through the use of inorganic materials such as silicon, CdTe and GaAs in solarcells. Despite the high conversion efficiency, these traditional inorganic solar cells are very expensive due to their highcosts of production. Because of this, alternative materials for use in solar cells are thus very important. Solar cells fromorganic materials offer some important advantages compared such as lightweight, potentially low-cost, environmentallyfriendly, no rare metals and minerals, no high temperature required during production and unlimited room for furthermaterial modification and improvement. Nevertheless, two significant problems of organic solar cells still need to beresolved; these include: a low power conversion efficiency and low stability. Bulk heterojunction organic solar cells arehighly promising and are those that have produced the best power conversion efficiencies.

In this work, bulk heterojunction solar cells made of blend of photoconductive polymer (P3HT) and different smallorganic molecules (PCBM, C60, TCNQ) have been fabricated and their quality assessed by their fill factor. Thedifferent heterojunction blends were (P3HT:PCBM, P3HT:C60 and P3HT:TCNQ) investigated.

Ni0.2Ti0.1Y0.16Zr0.54O2-AND Cu0.2Ti0.1Y0.16Zr0.54O2-AS ANODES FOR IT-SOFCs ANODE

Mihaela E. Trandafir1, Simona omcescu2, Jose Calderon-Moreno2, Petre Osiceanu2, Mihaela Florea11University of Bucharest, Faculty of Chemistry, Bucharest, Romania, 2Ilie Murgulescu Institute of Physical

Chemistry, Romanian Academy, Spl. Independentei 202, 060021, Bucharest, Romania

Solid oxide fuel cells (SOFC) offer a promising way of converting chemical energy into electrical energy with greatefficiency. SOFC devices need to possess simultaneously an ionic conductivity induced by the presence of oxygenvacancies and an electronic conductivity induced by the added metal together with a high porosity allowing the fueltransport through the anodic layer. Our goal is to develop a synthesis method that favors uniformity of the crystallinenetwork and an improvement of the ionic and electronic conductivity as well as of the catalytic activity. The self-assembling method using Triton X100 as template was used for synthesis of Ni0.2Ti0.1Y0.16Zr0.54O2- (NTYZ) andCu0.2Ti0.1Y0.16Zr0.54O2-(CTYZ).

The XRD pattern of sample CTYZ corresponds to a fluorite type (Fm3m) cubic stabilized zirconia phase with latticeparameter c= 5.112 . The cubic structure is stable at room temperature due to the incorporation of the yttrium,titanium and copper cations in the zirconia-based lattice and the formation of quaternary oxide solid solutionnanocrystals, with crystal size around 6 nm. The XRD pattern of sample NTYZ corresponds also to a fluorite type(Fm3m) cubic stabilized zirconia phase with lattice parameter c= 5.131 , with crystal size around 3.4 nm with the

present of bunsenite as minor phase. After calcination at 900 oC, the XRD pattern of sample shows a very significantgrowth of the crystallite size of the zirconia phase to about 17 nm, as well as a very small increase in the lattice

parameter, c= 5.134 .e structure (less than 5 vol.%), and crystal size of about 28 nm. The new composites show highmethane conversion and CO selectivity in the catalytic partial oxidation of methane. Conductivity results showed a

predominately n-type behaviour, highlighting a promising IT-SOFC anode.This work was supported by a grant of Partnerships in priority S&T domains Program (PNII), MENUEFISCDI,

project number 26/2012.

MODELING THE ELECTRON TRANSFER IN DYE-ELECTROLITE SYSTEMS FOR DYE-SENSITIZED

SOLAR CELLS

Anamaria Trandafir1,2,*, Corneliu I. Oprea1, and Mihai A. Girtu11Ovidius University of Constana, Department of Physics, 900527 Constana,Romania, 2University of Bucharest,

Faculty of Physics, 077125 Magurele-Ilfov, Romania, *Email:[email protected]

Dye-sensitized solar cells have gained widespread attention in the past few years due to low cost fabrication. Sincethe conversion efficiency of these photovoltaic systems highly depends on the electron transfer at the dye-electrolyteinterface, we studied the dye regeneration of various dye-electrolyte systems for dye-sensitized solar cells. Thesesystems are formed of various dyes (L0, D35 and Y123) and Co-based electrolytes. Using density functional theory(DFT) we determined the potential energy surfaces for the singlet, triplet and quintet states. We applied Marcus theory

to determine the electron transfer rate and reorganization energy for these systems. Optical characterization wasobtained using time dependent DFT for the dyes and electrolytes. Computations were made using the Gaussian03package.

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