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27th European Photovoltaic Solar Energy Conference and Exhibition; 75-77, We have proposed an integration method of hydrogenated amorphous silicon (a-Si:H) thin-film solar cells without using a conventional laser patterning method and realized a series connection of four unit a-Si:H-based solar cells. The method consists of using a glass substrate with many parallel straight-line trenches in it, metal oblique depositions (ODs), and dry etching of a-Si:H-based layers. The detailed fabrication process is composed of making parallel straight-line trenches in the glass substrate; depositing ZnO:Al film on it; wet etching of the ZnO:Al film; depositing a-Si:H-based layers; aluminum (Al) ODs; dry etching of the a-Si:H-based layers using the Al layer as a mask; and Al OD to overlap the Al back electrode with the front ZnO:Al electrode in the trenches, connecting unit cells electrically in series. The open circuit voltage (Voc) of the integrated cell was the sum of each Voc of the four unit cells and the current flowing through the integrated solar cell was determined by the unit cell with a minimum current value. The low fill factor of the integrated cell resulted from the high contact resistance between the two electrodes. The width of dead area from this integration method was only about 22 μm, which is much narrower than that in a typical a-Si:H-based solar cell fabricated by the conventional laser patterning method. This integration method has the advantage of being a simple and effective self-alignment process without laser scribing.

27th European Photovoltaic Solar Energy Conference and Exhibition; 340-343, PV-module backsheets are important for module reliability. They provide a humidity barrier to prevent corrosion, withstand UV-exposure and add mechanical stability. They electrically insulate the module circuits but also contain openings for the electrical connections to the outside world. In addition they should be lightweight and low cost. Here we report on a novel backsheet, contacfoil®-back, consisting only of an aluminium and dielectric layer compound. The aluminium, an excellent moisture barrier, faces the outside world and acts as a mechanically stable, UV-proof protective layer. On the inside, the dielectric layer isolates the module circuit from the aluminium backside. This dielectric layer becomes adhesives during lamination and a mechanically stable module compound is formed at the same time. The backsheet is opened at the locations where the electrical connections to the module circuitry have to be provided. In addition, we will discuss the possibility to connect to the module circuit via contact islands carved into the metal foil by selectively removing the aluminium with laser ablation. This allows connecting to the module circuit without mechanically opening the backsheet, which has a positive impact on module reliability.

27th European Photovoltaic Solar Energy Conference and Exhibition; 298-300, Ge wafers have been used as substrates for the growth of III–V based tandem solar cells because of the ideal lattice match. However, Ge wafers are high cost and the bandgap of Ge is too small which limits its contribution to the voltage output. Using epitaxial Ge on Si as template for III–V growth is a promising solution. Si has much higher bandgap and lower cost than Ge. Epitaxial Ge film with low dislocation density and smooth surface is desired for III–V growth. Since the substrate temperature could significantly influence the film property, it is investigated to optimize the deposition condition for Ge epitaxial growth. To compare the microstructure of the Ge films deposited at different substrate temperatures, the surface morphology was analyzed by atomic force microscopy (AFM), structural property of the films was examined by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). Ge film deposited at high substrate temperature exhibits good crystallinity, low dislocation density and rough surface.

27th European Photovoltaic Solar Energy Conference and Exhibition; 7-10, Plasmonics – collective oscillations of electrons in a conductor are of rapidly increasing interest for photovoltaics, with the ability to manipulate and confine light at the nanoscale opening up new solar cell design possibilities. Progress in harnessing plasmonics for photovoltaics is reviewed, highlighting both the promise and challenges. New applications include an investigation of the use of extraordinary optical transmission (EOT) to allow metals to replace transparent conducting oxides for thin-film solar cells and compact time asymmetric structures. Results are applicable to wafer-based and thin-film cells, as well as to advanced cell concepts.

27th European Photovoltaic Solar Energy Conference and Exhibition; 67-69, The concept of III-V based high efficiency solar cells on silicon substrates relies on suitable Si(100) preparation prior to III-V-on-Si heteroepitaxy. The method of choice for large scale III-V growth is metalorganic vapour phase epitaxy (MOVPE), due to excellent control of material composition and quality and scalability of production. One of the fundamental problems for III-V-on-Si growth relates to the difference in atomic structure which manifests itself in the polarity of the III-V material as opposed to the non-polar nature of the silicon substrate. As a consequence, the step structure of the substrate is vital for defect-free heteroepitaxy, with single layer steps on the substrate initiating anti-phase disorder in the III-V material, while a double-layer stepped substrate in principle enables anti-phase-free III-V growth. While UHV preparation of double-layer stepped Si(100) is well established, less is known about comparable preparation methods in the hydrogen-based MOVPE environment. We have investigated step formation on Si(100) in this environment and have established suitable preparation procedures for double-layer steps on Si(100) substrates with different misorientations.

27th European Photovoltaic Solar Energy Conference and Exhibition; 63-66, Large scale silicon nanohole textured solar cell with radial p-n junctions was demonstrated via a low cost, maskless method with laser annealed silver particle catalytic wet etching and phosphoric acid diffusion. Under 1 sun AM1.5G illumination, a Si nanohole solar cell exhibited an open-circuit voltage of 558 mV, a short-circuit current density of 29.1 mA/cm2, and a remarkable power conversion efficiency of 9.5%. The quasi-random nanohole geometry demonstrates a low cost and viable method for enhanced light absorption and performance of solar energy conversion. The nanohole texturing has been studied as a good anti-reflection technique for thin film solar cell. The device fabrication techniques used are transferrable to thin film photovoltaic applications.

27th European Photovoltaic Solar Energy Conference and Exhibition; 335-339, The focus of this work was set on studying the reliability of solar modules with cells interconnected by means of conductive glues and conductive film. The solar cell design was varied from standard H-grid to cells without front busbars and without rear side pads to account for maximum cost savings in materials and process. Solar cells were processed in an industrial like environment with main modification to the screen layout for front and rear metallization. The results indicate that solar cells without front busbars can be connected with both conductive adhesive techniques as long as rear side pads are present: all tested samples did pass TC200, DH1000 and HF10 test requirements. For rear side pad-free cells only the conductive film is capable to withstand moisture and thermal induced mechanical stress and corrosion during test. Solar cell samples without front busbars and rear pads interconnected with this technology did pass all environmental tests and do offer a great opportunity for further cost savings on cell level. Additionally, first work on busbar-free cells did reveal weaknesses of the front grid for conductive glue application which can be addressed in future work by simple modification to the screen layout.

27th European Photovoltaic Solar Energy Conference and Exhibition; 371-374, Silicon solar cells dominate photovoltaics but suffer from poor interaction with light. This work reports on progress regarding both spectral conversion and improved light interaction with the LIMA design [1]. This combines an efficient interdigitated back-contact (IBC) solar cell [2] with a silicon quantum dot (Si-QD) [3] to optimize the spectral distribution of the incident spectrum, and finally a front-side plasmon layer to optimize light interaction. Reflectivity after thickness and process optimization for a thin Ag layer and a Si3N4 shows that plasmonic particle layers reduce reflectivity compared with an IBC with only a Si3N4 anti-reflective coating layer. There is an increasing of the quantum efficiency in the infrared zone but losses remain in the UV zone which needs to be addressed.

27th European Photovoltaic Solar Energy Conference and Exhibition; 397-402, Quantum well solar cells (QWSC) are novel devices with the potential to achieve high efficiency in an alternative approach to tandem or cascade cells. Spectrally tuned quantum well solar cells were designed and fabricated to deliver enhanced performance under the specific spectral resource of Cyprus. Non-destructive techniques such as external quantum efficiency (EQE) and electroluminescence (EL) have been used to characterize the innovative devices and indicate differences in performance between quantum wells with different Indium content and number of wells. For the investigation of carrier injection mechanisms in the cells, examination of the current and temperature dependence of the EL characteristics has been performed. Preliminary results from EL tests displayed multiple peaks in the region of quantum wells whereas reduced radiative recombination was observed at higher temperatures due to thermal escape of carriers via tunnelling. Additionally EQE measurements displayed the effect of quantum wells in the short-circuit current of the cells by indicating redshift of the cut-off wavelength. Finally our initial studies have shown that there is an excellent agreement between the resulting EQE and EL curves.

27th European Photovoltaic Solar Energy Conference and Exhibition; 55-60, Upconversion of infrared photons has been established as a concept to mitigate transmission losses in solar cells. Higher upconversion efficiencies, however, are necessary, to enable a profitable application of upconverting components. In this paper, we examine the embedding of upconverting material into a photonic structure to increase upconversion efficiencies. The structure influences the upconversion efficiency in two ways: First, higher local field intensities increase the absorption and the population of higher excited states. Second, the local density of photonic states is modified by the structure. Thus, the probabilities of desired transitions can be increased. This work covers the design of a suitable model structure and its examination via various simulation methods, most importantly finite-difference time-domain simulations, combined with an upconverter rate-equation model. An increase of the upconversion efficiency by a factor of about 3.6 at an excitation irradiance of 200 Wm-2 is determined.

27th European Photovoltaic Solar Energy Conference and Exhibition; 318-321, Lead-tin telluride (PbXSn1-XTe) alloys are materials with good thermoelectric properties and also are semiconductors of current interest for possible applications as long wavelength infrared detectors. Polycrystalline telluride of the PbXSn1-XTe (0.0 ≤ X ≤ 1.0) alloys were synthesized by the direct fusion technique. The thin films of these materials were prepared by a hot wall deposition method on glass substrates at Tsub. = 230 - 330 oC and vacuum of about 10-5 Torr. The microstructure of films was characterized by XRD, SEM, EDX and AES. The thin film powder patterns matched the powder target patterns satisfactorily and indicated the absence of binary phases. The films showed a natural cubic structure. The SEM analyses show that the films are densely packed and have good mechanical adhesion. The as-grown PbXSn1-XTe films show p-type conductivity. Thermoelectric measurements of the films showed high values of room-temperature Seebeck coefficient ranging from 20 to 400 μV K-1, for SnTe to PbTe thin films, respectively. The conductivity of the films was in the range of = 3·101 – 1·104 Ω-1·cm-1. The increase of concentration of lead atoms leads to decrease of conductivity.

27th European Photovoltaic Solar Energy Conference and Exhibition; 344-348, Transparent wide-band polymers are used to attach current collecting grid of wire to antireflection TCO (Transparent Conducting Oxide) layer on silicon solar cell surface in Laminated Grid Solar Cell construction. Pressure-induced transition from dielectric into a high-conductivity state in thin polymer layer appears after low temperature lamination step. The polymer layer provides good cross conductivity, but having dielectric properties in the longitudinal direction. In the present work, the synthesis and study of conducting transparent thermoplasts, copoly(arylene ether ketones) (co-PAEKs), with different concentrations of phthalide-containing homopolymers were performed. Variation of the homopolymers ratio in co-PAEKs permitted the change of electronic structure and physical properties of the thermoplasts. Thermo mechanical curves were measured to determine the softening points and optimal curing temperatures of the copolymers. Co-PAEKs (VS169, VS170) provided good transparency in the range of 380÷1100 nm (T >87% for 15 μm films) and low contact resistivity (< 0.8 mΩcm2) in the system TCO/Polymer film/Metal, measured on test structures Si-substrate/TCO(IFO, ITO)/polymer film/copper wire. High softening point of thermoplastics (> 1500С) makes it possible to do additional encapsulation of LGCells with EVA and glass without any detriment to the previously formed TCO/polymer/wire contact.

27th European Photovoltaic Solar Energy Conference and Exhibition; 375-378, Simulation and experimental studies on luminescent down-shifting (LDS) effect based on Si-quantum dots dispersed in a silicon dioxide matrix are performed. We used a transfer matrix approach to simulate the optical properties of our structure. In order to take into account the presence of the LDS-layer, we modify the incoming photon flux seen by the cell, considering the Si-quantum dots absorption and emission with a fixed quantum yield (QY). The estimation of the Si-quantum dots QY has been performed by photoluminescence decay time measurements. Using the method described in [4], we find a QY between 25% and 35%.

27th European Photovoltaic Solar Energy Conference and Exhibition; 35-40, Silicon nanocrystals (Si NCs) embedded in Si-based dielectrics provide a Si-based high band gap material (1.7 eV) and enable the construction of all-crystalline Si tandem solar cells. However, Si nanocrystal formation involves high-temperature annealing which deteriorates the properties of any previously established selective contacts. The inter-diffusion of dopants during high-temperature annealing alters Si NC formation and limits the built-in voltage. Furthermore, most devices presented so far also involve electrically active bulk Si and therefore do not allow a clear separation of the observed photovoltaic effect of the quantum dot layer from that of the bulk Si substrate. A membrane route is presented for quantum dot based p-i-n solar cells to overcome these limitations. In this approach, the formation of both selective contacts is carried out after high-temperature annealing and therefore not affected by the latter. P-i-n solar cells are investigated with Si NCs embedded in silicon carbide in the intrinsic region. Open-circuit voltages of up to 370 mV are shown for the NC layer. An optical model of the device is presented for improving the cell current. Finally device failure due to damaged insulation layers is analysed by electron beam induced current measurements.

27th European Photovoltaic Solar Energy Conference and Exhibition; 430-432, The present research work aimed at developing an innovative photovoltaic module based on a glassfree lightweight and cost-effective encapsulation solution, easy and feasible to integrate in multifunctionality demanding applications such as BIPV and transport. The proposed solution is composed of an aluminium sheet as the backsheet and a transparent and monolithic glass fibre reinforced organic matrix composite as both, the encapsulant and frontsheet. The research work comprised encapsulation of commercial CIGS photovoltaic cells, being the composite manufactured through infusion process. Beyond the PV properties, the study was focused on the interface aluminium-composite, considered as a key factor for the performance of this approach. During the infusion process and curing of the composite the PV performance of the cells was not degraded, resulting in encapsulated cells with a 9.2%. After 200 thermal cycles (IEC 61646), a decrease in the electrical output of the cells was observed, but meeting the requirements of the standard. However, the pull-off adhesion strength was not affected by the cycles, remaining as high as 11MPa. These promising results will guide and motivate further studies of metal-composite encapsulation solutions devoted to integration purposes.

27th European Photovoltaic Solar Energy Conference and Exhibition; 285-289, Epitaxial deposition of high-quality GaAs layers on cost effective Si substrates is a quite desirable route to decrease III-V cell cost and guarantee mass production for very high efficiency solar cells for Photovoltaic concentration (CPV). Several techniques have been proposed for the deposition of SiGe virtual substrates. Among them we propose two different methods for the realization of Si-Ge virtual substrates. The first one based on PECVD deposition of graded Si-Ge microcrystalline and amorphous layers having different hydrogen content is nearest to others proposed PECVD approaches. The Si-Ge stacked layers are conditioned by laser crystallization and/or Solid Phase crystallization. The second one is an innovative proposal based on a the utilization of a deposition system developed in our laboratories which can assure simultaneous deposition and X-Y laser beam laser crystallization processing under vacuum. Preliminary results are very interesting showing a high degree of crystallinity of the Si/Ge layers realized layers.

27th European Photovoltaic Solar Energy Conference and Exhibition; 322-324, At present, transparent conducting oxides (TCOs) are still superior in performance to most other transparent conductors. Results on opto-electronic modeling and design optimization of TCOs are presented using a monolithically integrated CIGS cell configuration as case. For various cell dimensions and TCO characteristics, the cell output was determined for both bare TCOs and TCOs with a metallic grid. This study showed that considerable efficiency enhancement (17% in power output) can be achieved for metal grid TCO combinations compared to single TCOs. Conductivity improvement has been experimentally verified on both commercial ITO PET foil as well as on ZnO:Al coated glass with electrochemically deposited metal grids. Conductivities below 0,1 Ohm/sq were reached and 80 times and 400 times conductivity improvements were obtained at a transparency loss of only 3% and 6%, respectively. It was also found that electrochemical deposition results in more conductive and lower surface area covering grids than obtained by Ag-ink screen printing.

27th European Photovoltaic Solar Energy Conference and Exhibition; 353-357, One possibility to achieve higher efficiencies in solar cell systems is to integrate angularly selective photonic filters in order to decrease radiative losses. Thermodynamically, the use of an angularly selective filter and a concentrator are equivalent. In both cases the efficiency of solar cells is increased by a manipulation of the ratio of the solid angles from which light is received and into which light is emitted. This ratio enters the equation to calculate entropic losses connected to étendue: The larger this ratio gets, the lower the entropic losses will be and the higher is the potential efficiency of the solar cell system. The difference between concentration and angular confinement is the angle which is affected. In concentrating systems the angle of incidence is increased, whereas in angularly confined systems the angle of emission is decreased. Maximum efficiency is reached, if both angles are equal. Of course the angle of emission cannot get smaller than the angle of incidence. To achieve the highest efficiencies, both systems can be combined. For this reason a solar cell system that combines concentration and angular confinement is investigated and discussed. For a GaAs solar cell system, as it is assumed for the calculations, the Shockley-Queisser efficiencylimit with a perfect angular confinement is 41.71%, whereas in a system without any confinement the limit is 32.5%. Starting with this system, modified Bragg and quasi-Rugate filters are considered to approximate a realistic efficiency enhancement using real filters in a concentrator solar cell system.

27th European Photovoltaic Solar Energy Conference and Exhibition; 403-407, Eu(dbm)3Phen and Tb(dbm)3Phen complexes have been impregnated in ordered mesoporous silica nanoparticles, with an average size of 50-70 nm and a pore diameter centered at 2.8 nm, with the aim of increasing the luminescence for their application as down-shifters for multicrystalline silicon solar cells. The morphological, structural, textural and luminescent properties of the synthesized samples were characterized by N2 physisorption, Xray diffraction (XRD), transmission electron microscopy (TEM), UV-visible spectroscopy and photoluminescence (PL and PLE) measurements.

27th European Photovoltaic Solar Energy Conference and Exhibition; 41-43, A super-lattice (SL) solar cell has been proposed and demonstrated to adjust the current density of the sub-cell for a optimized tandem cell . To explore the potential as a high efficiency single-junction cell, a SLs cell was tested under optical concentration. Compared with a conventional multiple quantum wells (MQWs) cell and a reference GaAs cell, the SLs cell presented a promising enhancement in open-circuit voltage with increasing concentration ratio. A SLs solar cell could exhibit its best performance under a concentration condition. Compared with a bulk p-i-n cell, the SLs cell can exhibit a higher efficiency by the combination of an open-circuit voltage almost as large as the bulk cell and a larger short-circuit current.

27th European Photovoltaic Solar Energy Conference and Exhibition; 412-417, Recombination through quantum dots (QDs) is a major factor that limits efficiency of QD intermediate-band (IB) solar cells. Our proposal for a new IB solar cell based on type-II GaSb QDs located “outside” the depletion region of a GaAs p-n-junction aims to solve this problem. The important advantage of proposed heterostructure appears due to the “outside” location of IB. Such IB does not assist generation of additional leakage current flow through the depletion region. Carriers cannot escape from “outside” QDs through the buffer layer and the depletion region into GaAs substrate by tunneling because QDs are far from the depletion layer. Only solar photon or thermal assistance may enable electron escape from QDs. Such type-II QD IB solar cell concept promises an efficiency enhancement relative to that of GaAs solar cells.

27th European Photovoltaic Solar Energy Conference and Exhibition; 367-370, In this contribution the absorption by defect states in hydrogenated amorphous silicon (a-Si:H) photosensitive devices in the environment of resonant absorbing silver nanoparticles (Ag NPs) is investigated. The location of defects in the strong electromagnetic fields accompanied by the localized surface plasmon (LSP) resonance of the Ag NPs enable high transition rates between the defect states and the conduction band. This results in a significant signal for near infrared (NIR) photon energies in external quantum efficiency (EQE) measurements. Dominant transitions take place for defect levels with an energetic distance from the conduction band, equal to the LSP resonance energy. Introducing a boron doped layer in direct contact to the NPs leads to a decrease of the NIR EQE signal. This gives evidence for the existence of the NP induced defect states in the a-Si:H material. The p-type doping shifts the Fermi level towards or below the defect states resulting in their depletion. Therefore these states cannot contribute to sub bandgap photon absorption resulting in a decreased NIR EQE signal.

27th European Photovoltaic Solar Energy Conference and Exhibition; 314-317, The authors report the epitaxial growth of germanium (epi-Ge) thin films on Si(100) substrate at low substrate temperature of 350oC using reactive thermal chemical vapor deposition. Si2H6 and GeF4 are used as source gases. The influences of gas pressure and gas flow ratio of Si2H6/GeF4 on the properties of epi-Ge are investigated. The results indicate that low pressure leads to Stranski-Krastanov growth mode in which pyramidal structures develop on the surface of epi-Ge film, and, the size of pyramids as well as the surface RMS roughness can be reduced by increasing the gas pressure. Both the content of Ge and the crystallinity of the epitaxial films can be enhanced by increasing gas pressure and/or decreasing gas flow ratio of Si2H6/GeF4. The RMS roughness of epi-Ge films can be decreased largely when the gas flow ratio is lower than 3.0. The change of surface morphology is proved to be correlated with the reaction between GeF4 and the growth surface of films. By increasing gas pressure to 8.0torr and decreasing the gas flow ratio to 2.0, for 1.21μm-thick epi-Ge films, a threading dislocation density of ~7.0×105cm-2 is achieved, along with a surface RMS roughness of ~2.0nm.

27th European Photovoltaic Solar Energy Conference and Exhibition; 422-425, The purpose of this work is to gain an understanding of the fundamental optoelectronic properties of silicon nanowires (Si-NWs) affecting cell device performance, and in particular Si-NWs synthesized by metalassisted chemical etching of single crystalline silicon (c-Si) wafers. We conducted preliminary temperature- and power- dependent photoluminescence (PL) studies on n- and p- type nanostructured c-Si. Intense visible PL was observed which was attributed to carrier quantum confinement and trapping taking place in the resulting etched structures. The origin of these largely blue-shifted luminescent states is still not completely understood. Our study corroborates to the suggestion of Si nanocrystals formed by sidewall roughness induced from the etching process and /or to the presence of porosity within the formed structures.

27th European Photovoltaic Solar Energy Conference and Exhibition; 349-352, Most solar modules are manufactured using vacuum lamination technique, where the laminate stack is heated up under vacuum and then pressed together. During this process, the encapsulate material, which is embedding the solar cells and electrical interconnectors, is melting, flowing around the single components and, in the case of Ethylene-Vinylacetate (EVA), cross linking. The transition from a thermoplastic material to a non-melt able elastomeric material is achieved by a cross linking agent, which is incorporated by the foil manufacturer. The states of the art are peroxide cross linking agents which are activated at individual temperatures during the lamination process and lead to a covalently cross linked polymer network. In this work, we present a technique for EVA-cross linking by means of UV radiation. Instead of peroxide crosslinking agents, photo initiators are incorporated into the material. At first we describe the basic process of photo initiated cross linking and to understand the chemical interactions. EVA materials are then characterized towards their temperaturedepended cross linking behaviour under defined UV radiation.

27th European Photovoltaic Solar Energy Conference and Exhibition; 382-384, It is known that the light scattering from the metal particles deposited on the surfaces of cells can be used for increasing light trapping in the solar cells. In this work plasmonic structures is composite materials consisted of silver nanoparticles embedded in dielectric films of TiOx – used as cell antireflection coating. The films are deposited by sol-gel method using spin–on technique. Microstructure of prepared samples is analyzed by SEM observation. Good particles density was obtained by this simple, cheap and short time demanding method. We demonstrate that due to light scattering by metal particles the plasmonic-ARC layer is more effective than TiOx layer without Ag nanoparticles. Implementation of nanoparticles on bare cell surface was carried out too. Simulation studies on particles size were carried out as well.

27th European Photovoltaic Solar Energy Conference and Exhibition; 70-74, The development of a cost-effective high voltage solar cell that can be grown directly on a silicon-based solar cell can lead to a significant increase in efficiency over the present best monocrystalline silicon device. This achievement could lead to a significant reduction in the projected cost of solar generated electricity. Devices composed of groups III, IV, and V of the periodic table have been grown on silicon substrates. Each iteration, beginning with the single-junction windowless GaAsP solar cell and concluding with a GaAsP/SiGe tandem device, is analyzed and reported. GaAsP bandgap-voltage offsets achieve 0.54 in single-junction devices while dual-junction devices demonstrate a device toward AM1.5 15.2% efficiency with AR-correction and rear texturing.

27th European Photovoltaic Solar Energy Conference and Exhibition; 311-313, In this investigation Naphtalimide based Lumogen Violet organic dye [BASF] is characterized for inclusion in luminescent downshifting (LDS) layers. A PV device made up of an LDS layer of Lumogen Violet deposited on top of a crystalline silicon cell has been fabricated to improve its power conversion efficiency. External quantum efficiency measurements and outdoor tests for the PV/LDS devices are discussed. An analytical model was also developed to compare experiment results with the model predictions.

27th European Photovoltaic Solar Energy Conference and Exhibition; 393-396, We propose a simple method of silicon surface texturing/nano-structure growth using pure hydrogen with metal catalyst. This method, which does not need a filament current to generate hydrogen radicals like conventional hot filament methods, is quite simple and suitable for large area processing. A refractory metal was used as a catalyst for the hydrogen molecular cracking. Surface morphology of resultant samples were strongly depended on the reaction pressure and temperature. Texture structures and very fine silicon nanostructures can be obtained by controlling the process conditions. TEM results suggested that no dislocation or defects were created on the silicon surface by this process. A growth model of silicon whiskers and texturing mechanism are discussed based on the SEM results. It is concluded that the proposed method based on a modification of Si surfaces only by hydrogen radicals can be considered as a “green” technology, which can be used for the cost effective fabrication of Si based solar cells.

27th European Photovoltaic Solar Energy Conference and Exhibition; 305-310, It is well known that photovoltaic efficiency is strongly temperature dependent. As the temperature raises, the internal resistance of the material increases and the electrical conductivity decreases. This can be a major problem in building-integrated photovoltaic (PV) devices where free convection cooling is limited, especially during summer in hot climate such as in South Greece. Various existing techniques to lower PV panels’ temperature are initially presented in this paper. In this study focuses on the combination of a photovoltaic panel with a Phase Change Material (PCM) in order to reduce the daily temperature of the PV panel and improve the overall efficiency of the system. The experimental concept of integrating PCM on the PV panels located in the laboratory of Renewable and Sustainable Energy Systems, Technical University of Crete, Chania is presented. In Mediterranean climates there are very limited results of the behaviour of amorphous and microcrystalline silicon thin film solar cells modules when combined with PCMs.

27th European Photovoltaic Solar Energy Conference and Exhibition; 32-34, We propose to integrate photonic nanostructures coupled with Ge quantum dots (QDs) in crystalline Si solar cells for advanced management of photons and carriers. The photonic nanostructures at the surface can bring extra interaction between photons and QDs to result in efficient light trapping and increased photoresponse at infrared region. The type-II alignment at the Ge/Si interface would spatially separate electrons and holes to suppress carrier recombinations, and photogenerated carriers could be efficiently transported through electronic coupling of vertically aligned QDs. Importantly, the proposed nanostructures can be fabricated by a simple and practical method based on wet chemical process without any lithography techniques to utilize spontaneously modulted etching rate.

27th European Photovoltaic Solar Energy Conference and Exhibition; 433-435, The well-aligned ZnO nanostructures were fabricated on the as-deposited ZnO thin film by a novel reducing annealing process, the morphologies of ZnO nanostructures could be easily regrown and modified by adjusting the parameters in Mist CVD method at a low temperature process. The carrier gas was found as one of important factors influence on the surface area and morphology of nanostructures. The crystallinity of ZnO nanostructures were improved after regrowth process in Mist CVD. The obtained novel ZnO nanostructures with larger surface area are expected to be used as photo electrode instead of TiO2 in the dye-sensitized solar cell in the future.

27th European Photovoltaic Solar Energy Conference and Exhibition; 418-421, Ordered hexagonally arranged p-type silicon micro-rod arrays were fabricated by reactive ion etching (RIE) of c-Si wafer using a non-close-packed (ncp) polystyrene (PS) spheres template as a mask. The average reflectivity of Si micro-rod arrays is 8.8~10% in the wavelength range of 400~1100 nm for the rods with the length of 3~4 m. Intrinsic and n type a-Si:H thin film layers with the total thickness of about 15nm was deposited using hotwire chemical deposition (HWCVD) to form the quasi-radial heterojunction structure. Fairly nice conformal coverage was formed for both a-Si:H thin film and subsequent ITO front contact layers. The dark current-voltage (IV) measurements indicate that proper atomic H treatment before the a-Si:H thin layer deposition is benefit to improve the interface property of the heterojunction with micro-rod-array structure.

27th European Photovoltaic Solar Energy Conference and Exhibition; 333-334, Owing to the grid fingers shading induced optical loss in commercial silicon solar cell modules, the ethylene vinyl acetate (EVA) encapsulation layer incorporated with grid diffusers technique has been proposed to increase the external quantum efficiency (EQE). To reduce the reflection loss from grid fingers, the incoming light is scattered by the screen-imprinting diffusers and have more chances to reach the active cell area. The scattering properties of the encapsulation layer incorporated with grid diffuser are studied by the ray tracing method. By optimizing the distance between fingers and diffusers and adjusting the diffusing angle, the reflection could be reduced in the range of the wavelength from 400 nm to 1000 nm. A thermally curable acrylic resin with polystyrene (PS) beads is fabricated in the encapsulation layer via screen imprint process for a 5×5 cm2 solar module. Comparing to the conventional module, an EQE enhancement up to 5.2% of the module with grid diffusers in the encapsulation layer is achieved for the wavelength from 400 nm to 1000 nm. This study provides a possible concept to overcome the grid fingers shading as well as to increase the EQE for commercial PV modules.

27th European Photovoltaic Solar Energy Conference and Exhibition; 61-62, There are two main loss sources in solar cells which are the thermalisation and the non-absorption processes. Up to 30 to 50% of the solar spectrum power is lost by the second process, because of the intrinsic properties of semi-conductors. Whereas up-conversion process could reduce this loss, application to photovoltaics is limited by the up-conversion efficiency of materials. We propose to use a plasmonic structure to overcome this limitation, using erbium doped yttrium fluoride thin layer elaborated by ALD at 250°C as active up-converter material. Near infrared and visible up-conversion properties of samples have been characterized using a confocal microscope. Samples, having a thickness below 100 nm, deposited onto a gold mirror, exhibit significant upconversion. Plasmonic structures were fabricated by e-beam lithography, resist development, gold deposition and liftoff process. The confinement of the incident photon inside the structures and the resonance tuned at the absorption frequency of the ion allows the increase of the absorption of the Er3+. The measurement of the enhancement factor of structures associated with the plasmonic resonator has been performed by luminescence cartography. From these data, total average enhancement factor up to x45 has been achieved by the use of the plasmonic structures, with maximal values close to x450 for some frequencies, as compared to a layer deposited on a bare glass substrate.

27th European Photovoltaic Solar Energy Conference and Exhibition; 50-54, The light trapping design in this work indicates an increase of the effective path length by as much as a factor of 21. Simulations show that Jsc of 88%Ge content Ge:Si solar cell below Si with light trapping can be 130% higher than that without light trapping. Experimentally an increase in optical path length of 17X was achieved on 88%Ge content Ge:Si solar cells which were grown on low cost c-Si substrates by reduced pressure chemical vapor deposition (RPCVD) technology. A Jsc of 7.91mA/cm2 was obtained below Si at one sun. It is 120% higher than that of cells without light trapping. Below Si at 30 suns, the efficiency of 88%Ge content Ge:Si solar cell with light trapping reached 1.37% which is 60% of the modeled efficiency maximum.

27th European Photovoltaic Solar Energy Conference and Exhibition; 277-280, Commercially available quantum dots, encapsulated in a PMMA film were used as a luminescent down-shifting layer on CdS/CdTe photovoltaic devices. The application of these films resulted in the improvement of the short-circuit current by over 5%. Additionally, the contribution to total photocurrent generated from the short wavelength (≤500nm) part of the solar spectrum was increased by over 130%. The films have been shown to reduce the amount of light lost at = ≥550nm due to masking or scribing on the device by scattering the light onto the contact. At shorter wavelengths ( = ≤500nm) the isotropic emission of light achieves a similarn effect. This scattering sevres to increase the optical area of the contact. The efficiency gains shown in this paper are comparable to those shown by phosphors with scope for improvement as quantum dot luminescent quantum yields increase.

27th European Photovoltaic Solar Energy Conference and Exhibition; 281-284, The heterojunction cell concept enables high efficiencies and simultaneously low-cost production. Roth & Rau AG provide tools and processes for mass production of heterojunction technology (HJT) based solar cells. New low temperature interconnection techniques are needed for this cell concept. This work focuses on the evaluation of the characteristics of polymer pastes based on silver and copper particles. Therefore different curing atmospheres of an inert inline drying system (Rehm Thermal Systems) were used. The electrical resistance, adhesion, and solderability of the screen printed pastes were evaluated. As we will show in the present work, the currently available copper pastes can be an equivalent alternative to common used silver pastes.

27th European Photovoltaic Solar Energy Conference and Exhibition; 364-366, It has been analyzed that the local strain fields and the intermixing around Ge quantum dots (QDs) in the Si spacer by electron microscopy. HAADF-STEM images clearly show the intermixing between Ge and Si as well as the surface segregation of Ge become advanced. The average composition of the QDs is Geo.43Si0.57, which is almost constnt in a row of vertically aligned QDs. The local strain analysis obtained from the high-resolution TEM images shows that the strain state is remained after the elastic relaxation of QDs, however, most of the strain state has relaxed.

27th European Photovoltaic Solar Energy Conference and Exhibition; 328-332, The traditional connection technic applied to solar cells requires an expensive metallization and can lead to cell breakage because of mechanical stresses. Different alternatives, known as "low-stress", have been explored as reported by several articles [1], [2], [3]. Laser spot soldering, adhesive and mechanical contacting technology relying purely on contact pressure exerted by magnet or under pressure in the module interior have already been investigated and some of them are starting to be used in production. Nevertheless all of these solutions have some drawbacks like for instance, one very sharp process, costly material or components or bad interaction with other parts of the modules etc… In this paper, we discuss a PV module with electrical contacts achieved through a resilient device. The main issue in this simple approach concerns the pressure control which must stay consistent during all the 20 to 30 years of the module life. Modeling and simulation allowed determining the mechanical characteristic and the theoretically architecture of the specific elastic device. The Identification and characterization following routine durability tests of the adequate polymer is described and results are commented. Two small modules with four cells have been mounted and tested with success but a thirty six cells module failed during thermal cycling. Important details of implementation were revealed and taken into account in the process improvement. Industrial design of a sixties cells module including the resilient device is explained and the manufacturing process flow is described. The thermal cycling and exposure in natural environment was applied to this module in order to prove the potential durability of this solution.

27th European Photovoltaic Solar Energy Conference and Exhibition; 385-388, Silicon (Si) nanostructures which have potential use for solar cell have been synthesized by two steps. The silver nanoparticles were formed; and silver catalyzed etching was utilized to create Si nanostructures. The sizes of the nanostructures can be controlled by the formation and etching conditions. Further, the Si nanostructuretextured solar cells have been manufactured and tested. The optical reflection can be decreased to 5%. The optical property and current-voltage (I-V) measurement indicate that the Si nanostructure-textured solar cells will promisingly exhibit good performance if better passivation and electrode contact were provided. This fabrication method of Si nanostructures could open potential application in photovoltaic.

27th European Photovoltaic Solar Energy Conference and Exhibition; 389-392, Nanostructures based on amorphous/crystalline differences can be grown by a new fabrication process using common PV industry techniques. As for other nanostructures created by chemical variations, confinement properties may enhance carrier multiplication effects. For crystalline silicon test samples with embedded amorphous silicon nano-layer, an increase of quantum efficiency after etching of the passivation layer was experimentally observed. Considering results of previous works, an explanation based solely on the activation of electron multiplication was suggested. The simulation indicated that the extra energy required to generate a second electron was lower than the band gap. Therefore, Low-Energy Electron Multiplication (LEEM) was observed in singlejunction all-silicon device. LEEM could be further enhanced by spatial optimization of the nanostructures. This new effect opens perspectives for the development of ultra-high efficiency solar cells without concentrator and a family of disruptive optoelectronic products might emerge from these progresses.

27th European Photovoltaic Solar Energy Conference and Exhibition; 22-26, The intermediate band solar cell (IBSC) is a solar cell that, in order to increase its efficiency over that of single gap solar cells, takes advantage of the absorption of below-bandgap energy photons by means of an intermediate band (IB) located in the semiconductor bandgap. For this process to improve the solar cell performance, the belowbandgap photon absorption has to be effective and the IB cannot limit the open-circuit voltage of the cell. In this paper we provide a guide to the new researcher interested in the idea in order he can quickly become familiar with the concept and updated with the most relevant experimental results.

27th European Photovoltaic Solar Energy Conference and Exhibition; 27-31, The major challenge of multiple quantum wells (MQWs) solar cells is to sufficiently extract photoexcited carriers to the external circuit at the operation voltage through MQWs regions. The present study reports the effectiveness of compensation doping of the i-region, which includes MQWs, for more efficient transport of both electrons and holes. P-type unintentional doping exists in GaAs by inevitable carbon incorporation during MOVPE, causing undesired bending of the band-lineup in the i-region. By cancelling this out with n-type dopants, sulfur, we have achieved much high carrier collection efficiency of >90% at the operation bias voltage regardless of the excitation wavelength, compared to

27th European Photovoltaic Solar Energy Conference and Exhibition; 78-80, This paper shows a new bonding method for mechanically stacked multi-junction solar cells. Our strategy is the combination of conductive nanoparticle alignments and van der Waals bonding. Conductive nanoparticles, such as Pd, were aligned through the use of a self-assembled block copolymer template, and the domain size of 50 nm and the concentration of 1×1010 cm-2 were realized. With this method, reductions of bonding resistance and optical absorption loss were simultaneously attained for the use of mechanically stacked solar cells. It is possible to apply this method for various sorts of photovoltaic materials, such as Si, Ge, GaAs, InP, and CuInGaSe. As a demonstrative case, we examined a GaAs (Eg-1.4 eV)/InGaAsP (Eg-1.15 eV) two-junction solar cell fabricated with the new bonding method, and the total efficiency of 11.8% was achieved which was in good agreement with the theoretically predicted value. The bonding resistance was estimated to be 3.1 Ωcm2. These results suggested that this bonding method is highly useful for mechanically stacked multi-junction solar cells. The efficiency can be potentially improved over 30% by the appropriate combinations of solar cells under current matching.

27th European Photovoltaic Solar Energy Conference and Exhibition; 293-297, The reported work evaluates the advantages for a photovoltaic (PV) cell under illumination of combining energy production, storage and conversion of heat losses in a single passive system. It is shown that the storage of latent heat using phase change materials substantially delays the PV yield decay, and that the simultaneous use of a thermoelectric generator amplifies the yield. The combination of storage and conversion is also shown to induce three different responses for the system output power. It enables either an instantaneous burst or an output power stabilization over the complete daylight cycle or a delayed and schedulable burst. As a result our study validates the concept of using a passive system to handle the heat influence on a standard PV system, thus preventing the energy production and yield to be critically affected.

27th European Photovoltaic Solar Energy Conference and Exhibition; 358-360, We present a technique of mounting a condensing microlens array (MLA) on a solar cell for micromanipulation of the incident solar light. Two types of MLAs with square and cylindrical micropatterns were developed and then respectively mounted onto a triple junction GaAs solar cell as both an incident sunlight manipulator and a surface encapsulation layer. Under the air mass (AM) 1.5 irradiation, the square MLA-mounted cell with an optimal optical spacer showed short-circuit current (ISC) of 13.27 mAcm-2 and power conversion efficiency (PCE) of 22.25 %, and the same cell mounted with the cylindrical MLA with an optimal optical spacer showed similar ISC of 13.17 mAcm-2 and PCE of 22.10 %. The achieved output powers are ~19.5 % higher than that of the general glass-packaged cell as a reference and even 10 % higher than that of the pristine cell without a cover. The condensing MLA can replace a conventional glass (or film) as a encapsulation layer to efficiently improve photovoltaic performances of GaAs-based solar cells.

27th European Photovoltaic Solar Energy Conference and Exhibition; 290-292, We report on the optimization of growth temperature and As flux for fabrication of 1 eV GaInNAs solar cell using plasma assisted molecular beam epitaxy. Two sets of samples were grown at different temperatures and As beam equivalent pressures, keeping the As flux fixed in the first set and the growth temperature in the other. The p-i-n-solar cell structures were grown on n-GaAs(100) substrates. The output power exhibited a clear maximum within a narrow growth temperature and As pressure window. Based on this optimization, an AlInP-windowed GaInNAs p-i-n solar cell was grown on p-GaAs(100) substrate; the specific growth temperature was 440C and the As/III beam equivalent pressure ratio was ~10. This solar cell exhibited a short circuit current density of ~29 mA/cm2. Moreover, we demonstrated a GaInP/GaAs/GaInNAs triple junction solar cell that exhibited a short circuit current density of 12 mA/cm2 under real sun illumination.

27th European Photovoltaic Solar Energy Conference and Exhibition; 379-381, Si-Nanocrystals (Si-NCs), due to their superior optical and electrical properties compared to bulk-Si, are attractive for next generation photovoltaic applications. In particular, controlling bandgap by varying Si-NC size can be exploited for realizing low cost, environmental friendly, “all-Si” tandem solar cells. Tandem cells reduce the intrinsic heat losses (for photon energies higher than bandgap) and penetration loses (for photon energies lower than the band gap) of a single junction solar cell. Better understanding of formation and structural evolution of Si-NCs is crucial for realizing Si-NCs of tight size control. In view of this, Si-NCs were fabricated using SiO2/SiOx superlattice approach by Inductively Coupled Plasma Chemical Vapor Deposition (ICPCVD). Structural properties of the films and superlattices, in particular, structural modification of SiOx before and after annealing at 900 °C was studied using XPS, FTIR and Raman Spectroscopy characterizations. Formation of Si-NCs was confirmed by Raman spectroscopy. Complete effusion of hydrogen was observed on annealing.

27th European Photovoltaic Solar Energy Conference and Exhibition; 44-49, Current solar cells are fundamentally limited by their inability to harvest photons with energies less than the absorber optical threshold. Thinfilm solar cells, usually having band gaps above the optimum singlethreshold value of 1.34 eV given by the ShockleyQueisser limit, and a much smaller volume to absorb the light, are particularly prone to this loss mechanism and thus suffer from imperfect usage of the solar spectrum. An elegant way towards overcoming this limitation and using a larger fraction of the incident light is the reshaping of the solar spectrum by upconversion (UC) of photons. In the present work we apply photochemical upconversion, as realized by triplettriplet annihilation in organic molecules, to amorphous silicon thin film solar cells, incoherently transforming light from the 600750 nm to the 550600 nm wavelength range. Employing a moderate concentration of 19 suns, we demonstrate a relative gain of up to 3% in quantum efficiency around 700 nm and a relative overall efficiency increase of 0.2%. We further pinpoint a pathway which will allow significantly increasing the gain by UC and which can adapted to various single threshold devices, including organic and dyesensitized solar cells.