Symposium FG
Photovoltaic Solar Energy Conversion: Silicon and Beyond


Session FG-1 - Wafer-based Silicon and High-efficiency Solar Cells

FG-1:IL01  Direct Growth of III-V Compound Semiconductors on Silicon for High-efficiency Solar Cells
T. HANNAPPEL, O. SUPPLIE, S. BRÜCKNER, P. KLEINSCHMIDT, Helmholtz-Zentrum Berlin, Germany, and Ilmenau University of Technology, Germany; O. ROMANYUK, Academy of Sciences of the Czech Republic, Prague, Czech Republic; F. GROSSE, Paul-Drude Institut für Festkörperelektronik, Berlin, Germany

A microscopic understanding of the silicon preparation is a prerequisite for heteroepitaxial integration of III-V semiconductors on silicon for next-generation high-performance solar cells. For the formation of such a polar-on-nonpolar interface metalorganic vapor phase epitaxy allows to direct energetically and/or kinetically driven different step arrangements, either A- or B-type. The orientation of the III-V film depends on the atomic configuration of the Si(100) surface, as observed by optical in situ spectroscopy (reflection anisotropy spectroscopy, RAS) and confirmed by thorough surface science analytics in ultra-high vacuum. Utilizing the input of the optical analysis, an abrupt interface model can be applied to deduce the formation at the heterointerface, where Si-P bonds are found to be favorable. Ab initio density functional calculations of both abrupt and compensated interfaces are carried out. For P-rich conditions at abrupt interfaces, Si-P bonds are energetically favored over Si-Ga bonds. Following our DFT calculations, the energetically most favorable interface in thermodynamic equilibrium is the compensated interface with an intermixed interfacial layer.

FG-1:IL02  Crystalline Silicon for Wafer-based Solar Cells
DEREN YANG, State Key Laboratory of Silicon Materials and Department of Materials Science and Engineering, Zhejiang University, Hangzhou, China

Photovoltaic is one of main renewable energy, which has fast developed in the last decade. Many materials such as bulk, thin film, nano-dots and even organics have been used to fabricate solar cells. Among them, crystalline silicon including Czochralski (CZ) silicon and multicrystalline silicon is the absolutely major material used in photovoltaic industry, which usually occupies over 85% of the market shares. In the next decade, it is believed that they will keep this important position.
In recent years, to lower the cost and improve the quality of crystalline silicon wafers, lots of techniques have been developed in both of universities or industries all over the world. In this presentation, we will introduce the state-of-the-art silicon crystallization for wafer-based Si solar cells. At first, the progress for the growth of CZ Si and mc Si including larger size ingots, mono-casting ingots, germanium-doping, process simulation and so on is mentioned. Secondly, the behavior of impurities (oxygen, carbon, nitrogen and metals) and defects (dislocation and grain boundry) in crystalline silicon and their influence on solar cells is discussed. Finally, the techniques and problems of Si wafer cutting and thinning is also discussed.

FG-1:L03  Degradation Modeling of InGaP/GaAs/Ge Triple-junction Solar Cells Irradiated by Protons
S.I. MAXIMENKO1, M.P. LUMB2, S.R. MESSENGER1, R. HOHEISEL2, C. AFFOUDA1, D. SCHEIMAN1, M. GONZALEZ3, J. LORENTZEN1, P. P. JENKINS1, R.J. WALTERS1, 1Naval Research Laboratory, Washington, DC, USA; 2The George Washington University, Washington, DC, USA; 3Sotera Defense Solutions, Annapolis Junction, MD, USA

III-V-based multijunction (MJ) solar cells grown on Ge substrates are the primary leaders in space photovoltaic technology due to their high efficiency (~30%). However, a primary concern is a degradation of the end-of-life (EOL) performance due to electron and proton particle irradiation. While the effect of low and moderate irradiation-induced damage levels are understood rather well [1], limited data are available for multijunction cells irradiated to very high damage levels. In this work, we discuss damage mechanisms and their effect on multijunction solar cell performance. Characterization results for InGaP/InGaAs/Ge advanced triple-junction solar cells subjected proton irradiation with high damage doses up to 2E13 MeV/g are presented. Optoelectronic properties of each individual subcell and the microscopic nature of the damage mechanisms are analyzed. This is accomplished using electron beam induced current (EBIC) [2] and cathodoluminescence (CL) [3] modes of scanning electron microscopy (SEM). Based on the experimentally obtained data for the minority carrier transport properties, we used the NRL MultiBandsTM software package, consisting of both numerical and analytical drift-diffusion solvers, to explain and verify the experimental quantum efficiency and light current-voltage characteristics for different degradation levels.
[1] S. I. Maximenko et al., Nuclear Science, IEEE Transactions on, 57, 3095 (2010).
[2] S. I. Maximenko, et al., J. Appl. Phys. 108, 013708 (2010).
[3] S. I. Maximenko, et al., Apl. Phys. Lett, 94, 092101 (2009).

Session FG-2 - Thin-film Photovoltaics

FG-2:IL01  Current Status and Future Prospects of the CIGS PV Technology
H. SHIBATA1, A. YAMADA1, N. TERADA2, T. SAKURAI3, K. AKIMOTO3, 1Research Center for Photovoltaic Technologies, AIST, Central 2, Tsukuba, Ibaraki, Japan; 2Kagoshima University, Kagoshima, Kagoshima, Japan; 3Tsukuba University, Tsukuba, Ibaraki, Japan

Thin film solar cells based on chalcogenide materials such as CdTe and CIGS have emerged and have been leading thin film solar cell technologies.  A few GWs of modules have been produced annually.  Chalcogenide solar cells have advantages over other technologies in terms of performance, cost, long term stability, etc.
 In this presentation, the current status of CIGS solar cell technologies and the history of improvement in the performance of CIGS solar cells and modules will be first introduced.  A significant improvement in solar cell performance has been reported with conversion efficiencies of as high as η=20.8%, and the efficiencies of commercial modules have been improved up to η~15%.  The efficiency goal for 2030 is set to be η=30% for small area cells and η=25% for large-size modules, therefore improvement in conversion efficiencies for both cells and modules are required.  
Then, progress in CIGS technologies including our results will be introduced and the future direction in order to improve the competitiveness in the PV market will be also discussed.

FG-2:IL03  Transparent Conductors for Thin Film Solar Cells
R.E. TREHARNE, J.D. MAJOR, A. RAHSED, L.J. PHILLIPS, K. DUROSE, Stephenson Institute for Renewable Energy, University of Liverpool, Chadwick Building, Peach St, Liverpool, UK

A brief review of the role of TCOs as diffusion barriers, electrical blocking layers, antireflection and as transparent electrodes will precede recent results. In a combinatorial study of doped ZnO, each sample yielded up to 289 data points for conductivity, carrier concentration and optical transmission. Optimum dopant concentration was established and the dopant efficiency measured e.g. Si is a double donor. Plotting the plasma frequency vs carrier concentration yielded quantitative information about the non-parabolicity of the bands and carrier effective mass. The carrier dependence of mobility allowed for the development and verification of mobility models in TCOs. The combinatorial method was also used to study the influence of 'high resistive transparent'buffer layers in the series ZnO-SnO2 for CdTe/CdS solar cells. The composition giving the highest increases in Voc and FF was identified. Knowledge of the dispersion relations for the component layers of a thin film solar cell allows for the modelling of its optical utilisation. Here we report on the optimisation of the short circuit current in some solar cell designs by tuning of the transparent conductor, the high resistant transparent layer and the n-type layer, with the CdTe solar cell design being used as an exemplar.

FG-2:L04  Dynamics of the CdTe Activation Treatment: Effect on the Electrical and Structural Properties of the Absorber
A. ROMEO1, A. SALAVEI1, I. RIMMAUDO1, F. PICCINELLI2, D. MENOSSI3, A. BOSIO3, N. ROMEO3, 1LAPS-Laboratory for Applied Physics, Department of Computer Science, University of Verona, Verona, Italy; 2Department of Biotechnology, University of Verona, Verona, Italy; 3Physics and Earth Science Department, University of Parma, Italy

CdTe thin film solar cells have demonstrated high scalability, high efficiency and low cost fabrication process, remaining one of the real true alternatives to more expensive crystalline silicon technology.
One of the key factor that has allowed the success of this technology is the transformation of the absorber layer by an activation treatment where chlorine is reacting with CdTe in a controlled atmosphere or in air.
With this work we present a comprehensive analysis of the activation process by comparing the standard CdCl2 treatment (made by wet deposition in methanol solution) with treatments applied with chlorine containing gases. Different annealing temperatures and different amounts of CdCl2 have been applied. Also different concentrations of methanol solution have been taken into account.
Activated CdTe layers have been analyzed by means of X-Ray diffraction spectroscopy and atomic force microscopy, finished devices have been thoroughly analyzed by capacitance voltage, drive level capacitance profiling and admittance spectroscopy.
Shallow and deep defects have been identified for each particular activation treatment. Annealing temperature and Chlorine amount have been put in strict correlation with carrier concentration and with presence of defects.

FG-2:IL05  Junction Formation for Chalcopyrite Solar Cells
R. KLENK, Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany

Despite its complex microstructure the heterojunction between Cu(In,Ga)(S,Se)2 and chemical bath deposited CdS yields efficient solar cells with exceptional reproducibility. Other materials and processes for junction formation have been investigated for Cd-free cells and modules. Devices with such alternative buffer layers frequently show less ideal behavior such as lower open circuit voltage and fill factor or they need post-deposition annealing and light-soaking. In this contribution we will review the requirements for junction formation in terms of device physics and industrial application. We propose a device structure where junction formation is achieved by directly depositing a Zn(O,S)/ZnO:Al window layer by sputtering, thereby eliminating the need for a dedicated buffer layer. This approach already yields small area cells with efficiencies above 18% and scaling-up is underway.

FG-2:IL06  Current Status of Multijunction Thin-film Silicon Based Solar Cells: From State-of-the art Devices to Easthetic Building Elements
J.-W. SCHÜTTAUF, C. BALLIF, Ecole Polytechnique Fédérale de Lausanne (EPFL), Photovoltaics and Thin Film Electronics Laboratory, Neuchâtel, Switzerland

To improve the competitiveness of thin-film silicon solar cells, their conversion efficiency should be increased. A standard approach to reach higher efficiencies is to use multijunction cells. This is mostly done by fabricating tandem cells consisting of an amorphous silicon (a-Si:H) top cell, and a microcrystalline silicon (μc-Si:H) bottom cell. The highest efficiencies for thin-film silicon solar cells have so far been obtained with triple junction cells. In this invited lecture, we will address the current status of both tandem and triple cells, both in n-i-p and in p-i-n configuration, using different absorber materials such as a-Si:H, amorphous silicon germanium (a-SiGe:H), and μc-Si:H. Furthermore, the main challenges related to the fabrication and understanding of the different building blocks forming these devices will be addressed. In our lab we have recently fabricated a-Si:H/μc-Si:H tandem cells with a stabilized efficiency of 12.3%, similar to the current world record efficiency. For a-Si:H/μc-Si:H/μc-Si:H triple junction cells we have stable reached efficiencies of 13.0% (n-i-p) and 12.8% (p-i-n), respectively, slightly below the current record efficiency of 13.4%. An outlook on how to obtain stabilized efficiencies >14% will also be presented.

Session FG-3 - Emerging Technologies and New Concepts

FG-3:IL02  New Carbon-based Materials for the Preparation of Dye Sensitized Solar Cells
N. MARTÍN1, 2, J.L. DELGADO2, 1Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Madrid, Spain; 2IMDEA-Nanociencia, Facultad de Ciencias, Módulo CIX, 3ª planta, Ciudad Universitaria de Cantoblanco, 28049 Madrid, Spain

The development of new dyes for the preparation of Dye Sensitized Solar Cells, is a hot topic, due to the increasing global energy demand, which produce enhanced depletion of fossil fuels reserves, leading to further aggravation of the environmental pollution.
So far, a few examples of DSSC leading to power conversion efficiencies (PCE) of 11 % have been described, although further research is needed, in order to increase the PCE and the stability of the devices.
Our research group has a strong background on the preparation of light harvesting materials to prepare photovoltaic devices. In this regard recently we have described the posibility to regenerate the dye even with a small driving force of 150 mV , moreover these concept has been applied in the obtention of new efficient solar cells.
Considering these results, in this communication we will discuss on the progress carried out in our research group on the field of DSSC and the introduction of 3,6,9-substitued fluorene as promissing linking bridge between donor and accepting units.

FG-3:IL03  Unravelling Electronic Processes and Phenomena in Organic Materials through Polymer Scientists' Tools
N. STINGELIN, Imperial College London, London, UK

In the past decade, significant progress has been made in the fabrication of organic semiconductor thin-film devices predominantly due to important improvements of existing materials and the creation of a wealth of novel compounds. Many challenges, however, still exist. Key to commercial success is to make it technological practice to exploit the touted potential for low-cost manufacturing of these functional materials. This requires intimate knowledge of relevant structure/ processing/ performance interrelations. Here, examples are given of how polymer processing 'tools' may be utilized to gain further understanding of this interesting class of materials and how the physical organization, from the molecular to the macro-scale of functional organic matter such as polymer semiconductors can can be controlled. To this end, we present a survey on the principles of structure development from the liquid phase of this material family with focus on how to manipulate their phase transformations and solid-state order to tailor and tune the final 'morphology' towards technological and practical applications.

FG-3:L04  Thiol Functionalization: A Novel Class of Organic Additives for BHJ Solar Cells
A. OPERAMOLLA1, A. PUNZI1, O. HASSAN OMAR2, D. GENTILE1, D. BLASI1, F. BABUDRI1, G.M. FARINOLA1, 2, 1Dipartimento di Chimica, Università degli Studi di Bari Aldo Moro, Bari, Italy; 2CNR-ICCOM, Bari, Italy

Alkyl thiols are processing additives for bulk heterojunction (BHJ) solar cells useful for substituting post-production treatment with low energy consuming processes (1). They modify the solubility of donor:acceptor couple in the host solvent, impacting solid state nanoscale phase separation. After deposition, thiol solvent presumably evaporates from the blend. Conjugated structures with pending alkylthiol groups could be interesting for ternary blend (2) polymer solar cells. Such materials could not only optimize the active layer morphology, but contribute by means of their conjugated structure to light harvesting and charge generation processes operating in the solar cell.
Building on our experience in the synthesis of thiolated materials (3), we recently synthesized a family of organic semiconductors with low bandgap and pending alkylthiol groups. Their study in all organic or hybrid nanostructures represents an unexplored dimension in new generation photovoltaics. We present their synthesis and demonstrate the photovoltaic response of one of these compounds employed as additive in P3HT:PCBM solar cells.
(1) Solar Energy 2011, 85,1226; (2) Adv. Mater. 2013, 25, 4245; (3) J. Org. Chem. 2007,72, 10272; Eur. J. Org. Chem. 2011, 529; Curr. Org. Synth., 2012, 9, 764.

FG-3:IL06  New Pi-extended Building Blocks for Polymer Photovoltaics
K. TAKIMIYA, I. OSAKA, Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, Japan

The field of organic electronics has emerged as a potential technology enabling to realize low cost, ubiquitous, and soft electronics applications. One of the key materials in the technology is organic semiconductors that act as the active material in the electronic devices such as organic photovoltaic cells (OPVs).
Our research group has been involved in the development of organic semiconductors, in particular, conjugated polymer-based materials, where we have focused on fused-heterarene structures as the key building blocks. Such heteroarenes are isomeric naphthodithiophenes (NDTs) [1], naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole (NTz) [2], and naphthodithiophene diimide [3]. These heteroarenes can be efficiently synthesized and integrated into polymer backbones to provide new semiconducting polymers. In this presentation, design strategy and synthetic chemistry of these materials are discussed together with their electronic structures and OPV properties.
References: [1] Shinamura, S. et al. J. Am. Chem. Soc. 2011, 133, 5024. [2] Osaka, I. et al. J. Am. Chem. Soc. 2012, 134, 3498; Osaka, I. et al. J. Am. Chem. Soc. 2013, 135, 8834. [3] Fukutomi, Y.; Nakano M. et al. J. Am. Chem. Soc. 2013, 135, 11445.

FG-3:L08  The New Concept of Hybrid Perovskites for Photovoltaics: Understanding and Design by First-principles Calculations
A. FILIPPETTI, A. MATTONI, CNR-IOM UOS Cagliari, c/o Dipartimento di Fisica, University of Cagliari, Monserrato (CA), Italy

Hybrid perovskites (CH3-NH3)PbI3-xClx combining organic molecules (methylammonia CH3-NH3) with inorganic perovskites of the ABO3 type have been the rising-star materials of the latest and most promising frontier in photovoltaics developments. Solar cells based on CH3-NH3)PbI3-xClx as photon absorber, grown by inexpensive printing techniques reached record-high 15% efficiency. Impressively, in some experiments these hybrid perovskites were acting efficiently as both optically active and both n- and p-type transport material.
Our study unveil the most relevant sources of this excellent performance, i.e. large absorption coefficients (0.03-0.04 nm^−1 for wavelength of 500 nm) and small electron and hole effective masses, in turn related to peculiar characteristics such as the direct gap between highly dispersed Pb(6s)-I(5p) valence bands and Pb(6p) conduction bands. This understanding prefigures simple design rules to search for more hybrid perovskites with enhanced capabilities or specific requirements, such as the Pb replacement with non-toxic cations. The flexibility of the perovskite structure, which counts literally thousands of different materials, represents an ideal template for testing the widest range of atomic and molecular substitutions.

FG-3:IL10  New Concepts in Organic Photovoltaics
G. LANZANI, CNST@POLIMI, Istituto Italiano di Tecnologia e Department of Physics, Politecnico di Milano, Milan, Italy

In this talk I will review the state of art of most popular technologies in the organic and hybrid devices for energy. I will consider two perspectives: one scientific, about concepts, physical processes and materials, the other technological. Interface dynamics, as investigated by optical probes, will be described. Details will be given on the ongoing projects at CNST, that includes organic cells, hybrid solid cells, perovskytes, nanostructured electrodes for hydrogen production. A new device concept, based on polarization as an alternative to current, will be described.

FG-3:IL12  Coherent Electronic Energy Transfer and Organic Photovoltaics
E. COLLINI, Dipartimento di Scienze Chimiche, Università di Padova, Padova, Italy

One of the most surprising and significant advances in the study of the photosynthetic light- harvesting process is the discovery that the electronic energy transfer might involve long-lived electronic coherences, also at physiologically relevant conditions. This means that the transfer of energy among different chromophores does not follow the expected classical incoherent hopping mechanism, but that quantum-mechanical laws can steer the migration of energy. The implications of such quantum transport regime, although currently under debate, might have a tremendous impact in our way to think about natural and artificial light-harvesting and suggest new directions for the development of artificial devices for the efficient capture and re-use of solar energy.
Central to these discoveries has been the development of new ultrafast spectroscopic techniques, in particular two-dimensional electronic spectroscopy, which is now the primary tool to obtain clear and definitiv e experimental proof of such effects.

FG-3:IL14  Organic and Organometallic Molecules for DSSC
C. BAROLO, N. BARBERO, G. VISCARDI, Dipartimento di Chimica, NIS Centre of Excellence, Università di Torino, Torino, Italy; JH YUM, MD.K. NAZEERUDDIN, M. GRAETZEL, Laboratoire de Photonique et Interfaces, Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland; F. SAUVAGE, Laboratoire de Réactivité et Chimie des Solides, Université de Picardie Jules Verne, CNRS UMR 7314, Amiens, France; V. GIANOTTI, M. MILANESIO, Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Alessandria, Italy; S. FANTACCI, F. DE ANGELIS, Istituto CNR di Scienze e Tecnologie Molecolari (ISTM), c/o Dipartimento di Chimica, Università di Perugia, Perugia, Italy

Dye-sensitized solar cells have attracted significant attention as low-cost and colourful alternative to conventional solid-state photovoltaic devices. The heart of a dye-sensitized solar cell is a nanometer sized mesoporous titania film with a monomeric layer of a sensitizer. Both organic and organometallic molecules have been deeply investigated until now as efficient sensitizer systems yielding a conversion efficiencies over 12-13% (AM 1.5). In principle the optimal DSSC's sensitizer should have an absorption spectrum extended throughout the visible and the NIR region; however solar cells having specific colors are largely required for building integrated application.
Here we report some recent advances on different classes of dyes. Special attention will be paid to innovative, simple and reliable synthetic methods in order to obtain low cost sensitizers in different colors and with relatively high efficiency. Moreover the effect of the variables involved in the dye absorption process on titania films and their influence on stability and efficiency of the related cells will be also presented.

FG-3:L17  Synthesis of Rod-coil Diblock Copolymer with Different Approaches and its Use for the Passivation of CdSe Nanocrystals
S. ZAPPIA, S. DESTRI, ISMAC-CNR, Milano, Italy; M. STRICCOLI, M.L. CURRI, A.E. DI MAURO, CNR-IPCF, c/o Università di Bari - Dip. di Chimica, Bari, Italy; A. RIZZO, R. MASTRIA, CNR-Nano-NNL, Lecce, Italy

Conjugated polymers are characterized by the delocalization of π-electrons responsible of their electrical properties and structural rigidity. The manipulation of the chemical structures through the introduction of flexible chains allows to influence the morphology controlling the nanosegregation of the material.(1)
The use of nanocrystals (NCs) of inorganic semiconductors in "hybrid solar cells" offers high electron mobility enhancing the performance of the devices. The control of the active layer morphology at the nanoscale level ensures the further improve of the efficiency of the cells.(2)
The goal of this work is the evaluation of two approaches for the synthesis of rod-coil copolymer based on poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) rod-like block (electrondonor) and a coil block of poly(4-vinylpyridine) able to interact with semiconducting CdSe NCs (electronacceptor) with the aim of using it as both active and coordinating material for nanocomposites preparation with over 90% of NCs.
(1) Macromolecule 2009, 42, 9205.
(2) Solar Energy Materials & Solar Cells 2012, 98, 433.

Special Session FG-4 - Building Integrated Photovoltaics

FG-4:IL01  Novel Applications of High-concentration Photovoltaics
K. BARNHAM, Physics Department, Imperial College London, London, UK

The recent dramatic fall in the cost of first and second generation photovoltaic (PV) cells has been good news for solar installations which are rising exponentially world-wide. It has been bad news for European PV industry, for companies manufacturing high efficiency triple-junction cells and for the manufacturers of the high concentration CPV systems in which they are deployed. The first application of this 40% efficient third generation technology has been power generation in desert regions. Here the high direct insolation offers the possibility of comparable cost of electricity to first and second generation PV. This paper will discuss alternative applications of this technology where advantage can be taken of the cell efficiency being three times that of the second generation. Multifunctional applications of the technology will be discussed where the cost dynamic is not simply the need to undercut first and second generation prices. Examples will be given of the use of the cells in building integration and in the generation of solar fuels. A nano-structured triple-junction cell will be described which was developed at Imperial College London and which has achieved 42.5% cell efficiency in manufacture. The QuantaSol quantum well technology makes it possible to optimize the triple-junction cell for high energy harvesting in different solar spectra. This makes the cell particularly suitable for the very different spectra in many multi-functional applications and in locations other than deserts.

FG-4:IL02  Photonic Light Trapping in Thin-Film Solar Cells and in Luminescent Solar Concentrators
L.C. ANDREANI1, A. BOZZOLA1, S. FLORES DAORTA1, P. KOWALCZEWSKI1, M. LISCIDINI1, R. FUSCO2, D. TESTA2, 1Dipartimento di Fisica, Università degli Studi di Pavia, Pavia, Italy; 2ENI S.p.A, Research Center for Non-Conventional Energies - Istituto ENI Donegani, Novara, Italy

Efficient photovoltaic conversion of solar energy requires optimization of both light harvesting and carrier collection. This talk will discuss advanced concepts for photonic light trapping in two different kinds of photovoltaic systems, namely thin-film solar cells and fluorescent concentrators.
The first part deals with theoretical studies of thin-film silicon solar cells with various kinds of ordered and disordered photonic structures. Light trapping capabilities of these systems are analyzed by means of rigorous coupled-wave analysis and compared with the so-called Lambertian limit as given by a fully randomizing light scatterer. The best photonic structures are found to require proper combinations of order and disorder, and can be fabricated starting from pre-patterned rough substrates. Carrier collection is studied by means of full electro-optical simulations, which indicate that thin-film silicon solar cells can outperform bulk ones with comparable material quality, provided surface recombination is kept below a critical level.
The second part deals with luminescent solar concentrators (LSC), which are transparent slabs including luminescent dyes able to capture part of solar radiation and to concentrate it towards small solar cells put at their edges. We shall present studies of new fluorescent dyes developed by eni and characterized by low self-absorption, and of novel photonic concepts for increasing the concentration ratio and/or the conversion efficiency.

FG-4:IL03  Engineering Large Area Polymer and Hybrid Solar Cells

Polymer and hybrid (dye and perovskite) solar cells are promising low-cost technologies primed for migration from lab scale to large area devices. The scale-up is far from trivial and a number of issues need to be tackled in the design, processing and operation. This talk will focus on strategies developed in our laboratories for an efficient design and fabrication of modules.
Through PSPICE circuital design and architecture/materials optimization we show an effective scale-up of high performance dye solar cell (DSC) modules (efficiencies of 7%).
We report on the setting-up of an automated spray process, completely performed in air, in order to fabricate the first polymer modules where all the layers are fully spray coated.
We fabricated the first-ever solid state modules (eff. 5.1%) based on the emerging class of organometallic perovskites as active layer.
Plastics are incompatible with high T processing. We developed UV irradiation processes for fabricating fully plastic DSCs (eff. 5%) enabling us also to demonstrate the first W-type DSC module on plastic (eff. 3%).
Outdoor performance and properties such as transparency of these technologies make them particularly suitable for the integration into building facades as will also be outlined in this talk.

FG-4:IL04  Industrialization of Third Generation Photovoltaics
F. MATTEUCCI, R. GIANNANTONIO, DHITECH, Lecce, Italy; M. MANCA, IIT, Istituto Italiano di Tecnologia, Arnesano, (Le), Italy; G. GIGLI, NNL - National Nanotechnology Laboratory, CNR Istituto Nanoscienze, Distretto Tecnologico, Lecce, Italy

Third generation photovoltaics (3rd PV) will be hereinafter divided in organic photovoltaics (OPV) and dye sensitized solar cells (DSSC). The industrial development of glass-on-glass DSSC within the BIPV sector and OPV within the portable device field is still under progress, mainly due to short duration and/or low performances of large area devices. Medium term R&D on such devices is mainly focused on materials development and device aestethic optimization. Due to the relative easy processability of the materials involved in 3rd PV chemical companies are focusing their activities in developing low cost and/or more efficient materials, mainly in partnership with companies developing the devices. Despite the great market expectations for BIPV sector, glass-on-glass DSSC mass production is still under development and companies involved are trying to find compatible solutions of technical (device optimization in terms of production cost, long term stability and performances) and marketing issues (best product for smart windows in terms of aestethic and perfomances). As far as OPV is concerned, the market is ready to use such devices but stability and packaging issues are delaying its mass manufacturing.
Poster Presentations

FG:P03  Effect of the Thermal Annealing on the Nitrogen Concentration of N-doped TiO2 Thin Films Deposited by HiPIMS
C. STEGEMANN1, R.S. MORAES1, D.A. DUARTE3, 4, A.S. DA SILVA SOBRINHO1, M. MASSI1, 2, 1Technological Institute of Aeronautics, Plasmas and Processes Laboratory, São José dos Campos, SP, Brazil; 2Federal University of São Paulo, Institute of Science and Technology, São José dos Campos, SP, Brazil; 3Catholic University of Santa Catarina, Joinville, SC, Brazil; 4Federal University of Santa Catarina, Center of Mobility Engineering, Joinville, SC, Brazil

Nitrogen-doped titanium dioxide (N-TiO2) thin films have been extensively investigated in the last years for hydrogen generation due to its high catalytic activity under visible and near-infrared irradiation. The incorporation of nitrogen in the film lattice can occurs as either substitutional or interstitial doping. The substitutional doping is responsible by decrease the band gap energy and the interstitial doping is responsible by the decrease the quantum yield. Thus, in order to improve the catalytic activity of the N-TiO2 films, the N cannot be in the interstice of the lattice. In this work, N-doped TiO2 thin films were deposited on Si (100) wafers by reactive sputtering technique using a HiPIMS power supply that allows us to deposit crystalline thin film without heating the substrate. In order to modify and/or reorganize the N position on the TiO2 lattice, the films also passed by thermal annealing treatment. The band gap energy, the film structure, the surface chemical composition and binding energy were analyzed by Optical Spectrophotometry (OS), X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) before and after thermal annealing.
The authors thank the financial support of FAPESP (Grant 2011/50773-0),CNPq (Grant 555.686/2010-8) and CAPES

FG:P04  Environmental Friendly Solvents towards Roll-to-Roll Solar Cells Fabrication
A. CALABRESE, C. CARBONERA, A. COMINETTI, A. PELLEGRINO, A. SAVOINI, R. PO', Solar Energy Department Research Centre for Non-Conventional Energies, Istituto ENI Donegani, Eni S.p.A., Novara, Italy; D. KOTOWSKI, S. LUZZATI, Consiglio Nazionale delle Ricerche, CNR, Istituto per lo Studio delle Macromolecole, ISMAC, Milan, Italy

Polymer solar cells are attracting interest in the field of photovoltaic energy as a potentially low cost way of producing electricity from the sun. The recent findings of this technology have led several research groups to focus their attention to the conversion of the laboratory scale consolidated techniques to the roll-to-roll technology that uses printable inks. One of the key points when thinking to a scale-up concerns the quantities of the materials involved in the fabrication of the devices. As some of the chemicals used at the laboratory scale have a not negligible level of toxicity, the change of scale is not trivial when certain parameters have to be observed for safety reasons. Solvents are among the materials that are mainly involved in this issue, because of the quantities in use to prepare the printable inks that allow to deposit thin layers of the active material and accessory layers forming the devices. We present here the results of a study aiming to check the feasibility of substituting the commonly used chlorinated solvents by less toxic solvents without losing too much in terms of efficiency of the solar cells. The solvents under study allow the preparation of the active layer ink composed by an alternating donor-acceptor polymer and a fullerene derivative.


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