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Amorphous Silicon (amorphous + silicon)
Selected AbstractsIdentification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous SiliconADVANCED FUNCTIONAL MATERIALS, Issue 14 2009A. Harv Mahan Abstract Utilizing the concepts of a critical crystallite size and local film inhomogeneity, it is shown that nucleation in thermally annealed hydrogenated amorphous silicon occurs in the more well ordered spatial regions in the network, which are defined by the initial inhomogeneous H distributions in the as-grown films. Although the film H evolves very early during annealing, the local film order is largely retained in the still amorphous films even after the vast majority of the H is evolved, and the more well ordered regions which are the nucleation center sites for crystallization are those spatial regions which do not initially contain clustered H, as probed by H NMR spectroscopy. The sizes of these better ordered regions relative to a critical crystallite size determine the film incubation times (the time before the onset of crystallization). Changes in film short range order upon H evolution, and the presence of microvoid type structures in the as grown films play no role in the crystallization process. While the creation of dangling bonds upon H evolution may play a role in the actual phase transformation itself, the film defect densities measured just prior to the onset of crystallization exhibit no trends which can be correlated with the film incubation times. [source] Ultrahigh-Crystalline-Quality Silicon Pillars Formed by Millimeter-Wave Annealing of Amorphous Silicon on GlassADVANCED MATERIALS, Issue 29 2009Fude Liu Silicon pillars are formed by millisecond-long, single-pulse annealing of 110,GHz millimeter-wave radiation incident upon intrinsic amorphous silicon (a-Si) thin films deposited on glass by hot-wire chemical vapor deposition. The image was taken at a sample tilt angle of 52° for a better 3D view. [source] Characterization of Charge Collection in Photodiodes under Mechanical Strain: Comparison between Organic Bulk Heterojunction and Amorphous SiliconADVANCED MATERIALS, Issue 18 2009Tse Nga Ng Both gradual electrical changes and device failure mechanisms caused by mechanical strain in organic photodiodes are investigated and compared to a-Si:H deposited on plastic substrates. [source] Amorphous silicon-based multilayers for photovoltaic applicationsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010M. Zeman Abstract Multilayer (ML) structures were fabricated by alternating deposition of hydrogenated amorphous silicon (a-Si:H) and amorphous silicon nitride (a-SiNx:H) using plasma enhanced chemical vapour deposition. The ML structures were grown with and without hydrogen dilution of the source gas mixture. A blue shift of the absorption spectra was observed upon reduction of the a-Si:H thickness below 5 nm. Hydrogen dilution was found to improve the abruptness of the interfaces between subsequent a-Si:H and a-SiNx:H layers to below 1 nm. In order to investigate the potential of a-Si:H based ML structures as absorbers in solar cells and to study transport perpendicular to the interfaces, we have incorporated ML absorbers in a single junction p-i-n solar cell. We have determined the J-V characteristics and the external quantum efficiency of solar cells with a 60 period ML absorber, composed of 5 nm thick a-Si:H and 1 nm thick a-SiNx:H layers. The solar cell with ML absorber operated at efficiency of 1.8% (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Amorphous silicon based p-i-i-n photodetectors for point-of-care testingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010Marc Sämann Abstract Modern medical diagnostics demands point-of-care testing (POCT) systems for quick tests in clinical or out-patient environments. This investigation combines the Reflectometric Interference Spectroscopy (RIfS) with thin film technology for a highly sensitive, direct optical and label-free detection of proteins, e.g. inflammation or cardiovascular markers. Amorphous silicon (a-Si) based thin film photodetectors replace the so far needed spectrometer and permit downsizing of the POCT system. Photodetectors with p-i-i-n structure adjust their spectral sensitivity according to the applied read-out voltage. The use of amorphous silicon carbide in the p-type and the first intrinsic layer enhances the sensitivity through very low dark currents of the photodetectors and enables the adjustment of their absorption characteristics. Integrating the thin film photodetectors on the rear side of the RIfS substrate eliminates optical losses and distortions, as compared to the standard RIfS setup. An integrated Application Specific Integrated Circuit (ASIC) chip performs a current-frequency conversion to accurately detect the photocurrent of up to eight parallel photodetector channels. In addition to the optimization of the photo-detectors, this contribution presents first successful direct optical and label-free RIfS measurements of C-reactive protein (CRP) and D-dimer in buffer solution in physiological relevant concentrations. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Autodiffusion: a novel method for emitter formation in crystalline silicon thin-film solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2007A. Wolf Abstract The in situ formation of an emitter in monocrystalline silicon thin-film solar cells by solid-state diffusion of dopants from the growth substrate during epitaxy is demonstrated. This approach, that we denote autodiffusion, combines the epitaxy and the diffusion into one single process. Layer-transfer with porous silicon (PSI process) is used to fabricate n-type silicon thin-film solar cells. The cells feature a boron emitter on the cell rear side that is formed by autodiffusion. The sheet resistance of this autodiffused emitter is 330,,/,. An independently confirmed conversion efficiency of (14·5,±,0·4)% with a high short circuit current density of (33·3,±,0·8) mA/cm2 is achieved for a 2,×,2,cm2 large cell with a thickness of (24,±,1) µm. Transferred n-type silicon thin films made from the same run as the cells show effective carrier lifetimes exceeding 13,µs. From these samples a bulk diffusion length L,>,111,µm is deduced. Amorphous silicon is used to passivate the rear surface of these samples after the layer-transfer resulting in a surface recombination velocity lower than 38,cm/s. Copyright © 2006 John Wiley & Sons, Ltd. [source] Back Cover: Fundamentals of Metal-induced Crystallization of Amorphous Semiconductors (Adv. Eng.ADVANCED ENGINEERING MATERIALS, Issue 3 2009Mater. The Backcover shows a covering layer of aluminum lowers the crystallization temperature of amorphous silicon (a-Si). First the a-Si covers ("wets") the grain boundaries in the aluminum layer (Al). Once the wetting a-Si film has reached a critical thickness, crystallization starts at the grain boundaries. More details can be found in the article by E. J. Mittemeijer on page 131. [source] Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous SiliconADVANCED FUNCTIONAL MATERIALS, Issue 14 2009A. Harv Mahan Abstract Utilizing the concepts of a critical crystallite size and local film inhomogeneity, it is shown that nucleation in thermally annealed hydrogenated amorphous silicon occurs in the more well ordered spatial regions in the network, which are defined by the initial inhomogeneous H distributions in the as-grown films. Although the film H evolves very early during annealing, the local film order is largely retained in the still amorphous films even after the vast majority of the H is evolved, and the more well ordered regions which are the nucleation center sites for crystallization are those spatial regions which do not initially contain clustered H, as probed by H NMR spectroscopy. The sizes of these better ordered regions relative to a critical crystallite size determine the film incubation times (the time before the onset of crystallization). Changes in film short range order upon H evolution, and the presence of microvoid type structures in the as grown films play no role in the crystallization process. While the creation of dangling bonds upon H evolution may play a role in the actual phase transformation itself, the film defect densities measured just prior to the onset of crystallization exhibit no trends which can be correlated with the film incubation times. [source] Silicon Inverse-Opal-Based Macroporous Materials as Negative Electrodes for Lithium Ion BatteriesADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Alexei Esmanski Abstract Several types of silicon-based inverse-opal films are synthesized, characterized by a range of experimental techniques, and studied in terms of electrochemical performance. Amorphous silicon inverse opals are fabricated via chemical vapor deposition. Galvanostatic cycling demonstrates that these materials possess high capacities and reasonable capacity retentions. Amorphous silicon inverse opals perform unsatisfactorily at high rates due to the low conductivity of silicon. The conductivity of silicon inverse opals can be improved by their crystallization. Nanocrystalline silicon inverse opals demonstrate much better rate capabilities but the capacities fade to zero after several cycles. Silicon,carbon composite inverse-opal materials are synthesized by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals. The amount of carbon deposited proves to be insufficient to stabilize the structures and silicon,carbon composites demonstrate unsatisfactory electrochemical behavior. Carbon inverse opals are coated with amorphous silicon producing another type of macroporous composite. These electrodes demonstrate significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increases the material conductivity but also results in lower silicon pulverization during cycling. [source] Ultrahigh-Crystalline-Quality Silicon Pillars Formed by Millimeter-Wave Annealing of Amorphous Silicon on GlassADVANCED MATERIALS, Issue 29 2009Fude Liu Silicon pillars are formed by millisecond-long, single-pulse annealing of 110,GHz millimeter-wave radiation incident upon intrinsic amorphous silicon (a-Si) thin films deposited on glass by hot-wire chemical vapor deposition. The image was taken at a sample tilt angle of 52° for a better 3D view. [source] Semiconducting Thienothiophene Copolymers: Design, Synthesis, Morphology, and Performance in Thin-Film Organic TransistorsADVANCED MATERIALS, Issue 10-11 2009Iain McCulloch Abstract Organic semiconductors are emerging as a viable alternative to amorphous silicon in a range of thin-film transistor devices. With the possibility to formulate these p-type materials as inks and subsequently print into patterned devices, organic-based transistors offer significant commercial advantages for manufacture, with initial applications such as low performance displays and simple logic being envisaged. Previous limitations of both air stability and electrical performance are now being overcome with a range of both small molecule and polymer-based solution-processable materials, which achieve charge carrier mobilities in excess of 0.5,cm2 V,1 s,1, a benchmark value for amorphous silicon semiconductors. Polymer semiconductors based on thienothiophene copolymers have achieved amongst the highest charge carrier mobilities in solution-processed transistor devices. In this Progress Report, we evaluate the advances and limitations of this class of polymer in transistor devices. [source] High Electron Mobility in Room-Temperature Discotic Liquid-Crystalline Perylene Diimides,ADVANCED MATERIALS, Issue 21 2005Z. An Perylene diimide discotic columnar liquid-crystalline mesophases (see Figure) can show very high electron mobilities under ambient conditions. While the mobilities are strongly dependent on sample morphology and processing conditions, mobilities as high as 1.3,cm2,V,1,s,1 are measured, greater than that of amorphous silicon. [source] Liquid Crystalline Ordering and Charge Transport in Semiconducting MaterialsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 14 2009Wojciech Pisula Abstract Organic semiconducting materials offer the advantage of solution processability into flexible films. In most cases, their drawback is based on their low charge carrier mobility, which is directly related to the packing of the molecules both on local (amorphous versus crystalline) and on macroscopic (grain boundaries) length scales. Liquid crystalline ordering offers the possibility of circumventing this problem. An advanced concept comprises: i) the application of materials with different liquid crystalline phases, ii) the orientation of a low viscosity high temperature phase, and, iii) the transfer of the macroscopic orientation during cooling to a highly ordered (at best, crystalline-like) phase at room temperature. At the same time, the desired orientation for the application (OLED or field-effect transistor) can be obtained. This review presents the use of molecules with discotic, calamitic and sanidic phases and discusses the sensitivity of the phases with regard to defects depending on the dimensionality of the ordered structure (columns: 1D, smectic layers and sanidic phases: 2D). It presents ways to systematically improve charge carrier mobility by proper variation of the electronic and steric (packing) structure of the constituting molecules and to reach charge carrier mobilities that are close to and comparable to amorphous silicon, with values of 0.1 to 0.7,cm2,·,V,1,·,s,1. In this context, the significance of cross-linking to stabilize the orientation and liquid crystalline behavior of inorganic/organic hybrids is also discussed. [source] Role of a-Si:H bulk in surface passivation of c-Si wafersPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7 2010A. Illiberi Abstract The low thermal stability of hydrogenated amorphous silicon (a-Si:H) thin films limits their widespread use for surface passivation of c-Si wafers on the rear side of solar cells. We show that the thermal stability of a-Si:H surface passivation is increased significantly by a hydrogen rich a-Si:H bulk, which acts as a hydrogen reservoir for the a-Si:H/c-Si interface. Based on this mechanism, an excellent lifetime of 5.1 ms (at injection level of 1015 cm,3) is achieved after annealing at 450 °C for 10 min. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural order on different length scales in amorphous silicon investigated by Raman spectroscopyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010S. Muthmann Abstract Parameters for the structural short (SRO) and medium range order (MRO) of hydrogenated amorphous silicon (a-Si:H) films on the edge of the microcrystalline silicon (µc-Si:H) phase transition were studied with Raman spectroscopy. The observed samples were deposited using radio frequency plasma enhanced chemical vapor deposition. The studied films were grown with various constant and non-constant silane concentrations (SCs). A substrate dependent correlation of SC to the intensity ratio (IMRO) of the transversal acoustical (TA) and the transversal optical (TO) phonon bands was found. A strong correlation between width and position of the (TO) phonon band was observed. These two easily accessible parameters show an increase of SRO when IMRO decreases. [source] Shape transition of medium-sized neutral silicon clustersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2003A. Sieck Abstract Addressing the shape transition of silicon clusters, indicated by mobility experiments on silicon cluster cations with 24 to 30 atoms, we investigate the structure of low energy neutral silicon clusters with 25, 29, and 35 atoms within a density-functional based tight-binding approach. Since there is strong evidence for several nearly degenerate low-energy isomers for clusters of this size, we perform an extensive, but limited global search with Simulated Annealing and statistically analyze for each cluster size the 100 clusters with the lowest energy. We find different dominant shapes in the set of low energy clusters for each size. For neutral silicon clusters with 25 atoms, both prolate and spherical structures with low cohesive energies exist. For clusters containing 29 or 35 atoms, the low-energy isomers exhibit a spherical shape. For each cluster size several stable isomers with similar shapes, and hence similar mobilities, but different bonding patterns exist. The most stable 25 atom cluster resulting from our global search has the lowest energy within DFT-GGA known so far. Finally, we investigate the transition to diamond-like bonding patterns expected for larger silicon clusters. Clusters with up to 239 atoms resemble amorphous silicon rather than the diamond structure and contain several highly coordinated atoms. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Polycrystalline silicon thin films on glass obtained by nickel-induced crystallization of amorphous siliconPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010J. A. Schmidt Abstract In this work, we use the nickel-induced crystallization process to crystallize a-Si:H thin films at temperatures compatible with the utilization of glass substrates. Hydrogenated amorphous silicon films are deposited on planar float glass (Schott AF37) by plasma-enhanced chemical vapour deposition. The films, between 400 and 1400 nm thick, are grown intrinsic, slightly p-doped (p - ) or with a combined structure of heavily p-doped / slightly p-doped (p+/p - ) layers. On these films we sputter nickel with concentrations between 2.5×1014 and 3×1015 at./cm2, and then we anneal the samples in a standard nitrogen-purged tube furnace. The process evolves through the formation of the nickel silicide NiSi2, which has a lattice constant very similar to that of c-Si and acts as a nucleation centre. As a result of this thermal treatment we obtain thin polycrystalline films with a grain size over 100 ,m. The high crystallinity of the samples is confirmed through optical and electron microscopy observations, X-rays diffraction and Raman spectroscopy. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Polycrystalline Si films with unique microstructures formed from amorphous Si films by non-thermal equilibrium flash lamp annealingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010Keisuke Ohdaira Abstract Flash lamp annealing (FLA), with millisecond-order duration, can crystallize amorphous silicon (a-Si) films a few ,m thick on glass substrates, resulting in formation of polycrystalline Si (poly-Si) films with unprecedented periodic microstructures. The characteristic microstructure, formed spontaneously during crystallization, consists of large-grain regions, containing relatively large grains more than 100 nm in size, and fine-grain regions, including only 10-nm-sized fine grains. The microstructures results from explosive crystallization (EC), driven by heat generation corresponding to the difference of the enthalpies of meta-stable a-Si and stable crystalline Si (c-Si) states, which realizes lateral crystallization velocity on the order of m/s. The lateral crystallization may stop when the temperature of a-Si in the vicinity of c-Si, which is decided by both homogeneous heating from flash irradiation and thermal diffusion from c-Si, falls below a crystallization temperature. This idea is supported by the experimental fact that a lateral crystallization length decreases with decreasing pulse duration. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Amorphous silicon-based multilayers for photovoltaic applicationsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010M. Zeman Abstract Multilayer (ML) structures were fabricated by alternating deposition of hydrogenated amorphous silicon (a-Si:H) and amorphous silicon nitride (a-SiNx:H) using plasma enhanced chemical vapour deposition. The ML structures were grown with and without hydrogen dilution of the source gas mixture. A blue shift of the absorption spectra was observed upon reduction of the a-Si:H thickness below 5 nm. Hydrogen dilution was found to improve the abruptness of the interfaces between subsequent a-Si:H and a-SiNx:H layers to below 1 nm. In order to investigate the potential of a-Si:H based ML structures as absorbers in solar cells and to study transport perpendicular to the interfaces, we have incorporated ML absorbers in a single junction p-i-n solar cell. We have determined the J-V characteristics and the external quantum efficiency of solar cells with a 60 period ML absorber, composed of 5 nm thick a-Si:H and 1 nm thick a-SiNx:H layers. The solar cell with ML absorber operated at efficiency of 1.8% (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of the common mode rejection ratio of amorphous silicon balanced photodiodePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010D. Caputo Abstract In this work we report on the detailed characterization of an amorphous silicon/amorphous silicon carbide balanced photodiode structure suitable for differential photocurrent measurements. The device is a three-terminal structure constituted by two series-connected amorphous silicon p-i-n photodiodes. Two terminals are used to bias the two photodiodes at the same reverse voltage by the readout electronics. The output signal is the current difference between the two diodes, measured at the third terminal with a transimpedance circuit. Several devices have been fabricated with different areas and geometries utilizing four mask-step process. The devices have been characterized by means of common mode rejection ratio (CMRR) measurements as a function of the radiation wavelength and intensity. The CMRR measured under white light illumination has been found to lie around 37 dB in the whole range of investigated radiation intensities. The decrease of the CMRR observed at shorter wavelengths has been ascribed to mismatches and inhomogeneities in the surface and in the p-type window layer of the two hemi-devices. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modelling the light induced metastable effects in amorphous siliconPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2008G. Munyeme Abstract We present results of computer simulations of the light induced degradation of amorphous silicon solar cells. It is now well established that when amorphous silicon is illuminated the density of dangling bond states increases. Dangling bond states produce amphoteric electronic mid-gap states which act as efficient charge trapping and recombination centres. The increase in dangling bond states causes a decrease in the performance of amorphous silicon solar cells. To show this effect, a modelling approach has been developed which uses the density of localised states with exponentially increasing band-tails and dangling bond defect states distribution chosen according to the defect pool model. The calculation of the evolution of dangling bond state density during illumination has been achieved through a dynamic scaling relation derived from a defect creation model. The approach considers the amphoteric nature of the dangling bond state and thus accounts for the contributions of the different charge states of the dangling bond during the degradation process. This paper attempts to describe the simulation approach which calculates the defect density as a function of energy, position in the solar cell and illumination time. In excellent agreement with other workers, our simulation results show that the increase in the density of neutral dangling bond states during illumination is higher than of the charged states. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Kinetics of optically excited charge carriers and defects in hydrogenated amorphous silicon and related alloysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2004J. Whitaker Abstract Electron spin resonance and optically induced electron spin resonance measurements on hydrogenated amorphous silicon and germanium are useful probes of charge carriers in localized electronic states near the edges of the conduction and valence bands (band-tail states) and of defects, such as silicon and germanium dangling bonds. We review recent results on the recombination kinetics of charge carriers trapped in band-tail states. We also review recent results on the kinetics of metastable optically induced germanium dangling bonds in hydrogenated amorphous germanium. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The long-wavelength limit of the structure factor of amorphous silicon and vitreous silicaACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2010Adam M. R. De Graff Liquids are in thermal equilibrium and have a non-zero structure factor = = in the long-wavelength limit where is the number density, is the temperature, is the scattering vector and is the isothermal compressibility. The first part of this result involving the number (or density) fluctuations is a purely geometrical result and does not involve any assumptions about thermal equilibrium or ergodicity, so is obeyed by all materials. From a large computer model of amorphous silicon, local number fluctuations extrapolate to give = 0.035 0.001. The same computation on a large model of vitreous silica using only the silicon atoms and rescaling the distances gives = , which suggests that this numerical result is robust and perhaps similar for all amorphous tetrahedral networks. For vitreous silica, it is found that = , close to the experimental value of = obtained recently by small-angle neutron scattering. Further experimental and modeling studies are needed to determine the relationship between the fictive temperature and structure. [source] Helianthos: Roll-to-Roll Deposition of Flexible Solar Cell ModulesPLASMA PROCESSES AND POLYMERS, Issue 3 2007Edward A. G. Hamers Abstract In the development of the roll-to-roll deposition of amorphous silicon by means of plasma enhanced chemical vapor deposition, a number of different plasma aspects have been of importance. First, the understanding of process windows in terms of a dust free plasma has led to the formulation of an empirical scaling law for the dust free to dust forming transition in terms of the crucial process parameters such as, e.g., power and gas flows. Second, the homogeneity of deposition on an effective width of 30 cm has been demonstrated to be better than 5%. Increasing the deposition rate might be achieved by increasing the power density, but it scales only as (power density)0.77. A last important issue in roll-to-roll processing of long runs is process stability and on-line quality control. The accurate measurement of self bias voltage and optical thickness of the deposited stacks have proven to be very useful in this context. [source] Thin film solar cells incorporating microcrystalline Si1,xGex as efficient infrared absorber: an application to double junction tandem solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 1 2010Takuya Matsui Abstract We have fabricated efficient (,7,8%) hydrogenated microcrystalline Si1,xGex (µc-Si1,xGex:H, x,,,0.1,0.17) single junction p-i-n solar cells with markedly higher short-circuit current densities than for µc-Si:H (x,=,0) solar cells due to enhanced infrared absorption. By replacing the conventional µc-Si:H with the µc-Si1,xGex:H as infrared absorber in double junction tandem solar cells, the bottom cell thickness can be reduced by more than half while preserving the current matching with hydrogenated amorphous silicon (a-Si:H) top cell. An initial efficiency of 11.2% is obtained for a-Si:H/µc-Si0.9Ge0.1:H solar cell with bottom cell thickness less than 1,µm. Copyright © 2009 John Wiley & Sons, Ltd. [source] Simulation of losses in thin-film silicon modules for different configurations and front contactsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2008Kristijan Brecl Abstract A simulation tool for the quantification of electrical losses in thin-film modules using a one- and two-dimensional electrical PSpice model is presented. Two main sources of electrical losses are examined: monolithic contacts (MC) and front contacts made of a transparent conductive oxide (TCO) layer with or without a metal finger grid. Our study was focussed on amorphous and micromorph silicon modules in substrate or superstrate configuration. Results show that front contact losses (TCO losses and finger losses) prevail. While, under assumption that their subcell performances are the same, performance of amorphous silicon (a-Si) modules do not depend on the configuration, the superstrate micromorph silicon module has a relatively slight (below 2%) advantage over the substrate counterpart due to lower electrical losses in the MC. Losses of the front contact made of a thick TCO layer or of thin TCO layer and metal finger grid on top were studied for both modules in substrate configuration and optimisation results are presented. Use of thin TCO layer and optimised finger grid and solar cell geometry is competitive and these modules can even outperform the optimised amorphous or micromorph silicon module with thick TCO front contact. In all optimised cases under standard test conditions, total relative losses can be minimised to around 10%. Copyright © 2008 John Wiley & Sons, Ltd. [source] Investigation to estimate the short circuit current by applying the solar spectrumPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 3 2008Jun Tsutsui Abstract The influence of the solar spectrum is investigated to estimate the outdoor short circuit current (Isc) of various photovoltaic (PV) modules. It is well known that the solar spectrum always changes. Hence, it is rare to fit the standard solar spectrum AM1·5G defined in standard IEC 60904-3. In addition, the spectral response (SR) of PV module is different depending on the material. For example, crystal silicon (c-Si) has broad sensitivity that the wavelength range is between 350 and 1150,nm; meanwhile, amorphous silicon (a-Si) has relatively narrow sensitivity comparing to c-Si. Since Isc of the PV module decides by multiplying the solar spectrum and SR together, it is necessary to investigate the solar spectrum to estimate the outdoor Isc in addition to the solar irradiance and module temperature. In this study, the spectral mismatch is calculated and the outdoor Isc is estimated in the whole year. Copyright © 2007 John Wiley & Sons, Ltd. [source] A comparative study on cost and life-cycle analysis for 100,MW very large-scale PV (VLS-PV) systems in deserts using m-Si, a-Si, CdTe, and CIS modulesPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 1 2008Masakazu Ito Abstract This paper is a study of comparisons between five types of 100,MW Very Large-Scale Photovoltaic Power Generation (VLS-PV) Systems, from economic and environmental viewpoints. The authors designed VLS-PV systems using typical PV modules of multi-crystalline silicon (12·8% efficiency), high efficiency multi-crystalline silicon (15·8%), amorphous silicon (6·9%), cadmium tellurium (9·0%), and copper indium selenium (11·0%), and evaluated them by Life-Cycle Analysis (LCA). Cost, energy requirement, and CO2 emissions were calculated. In addition, the authors evaluated generation cost, energy payback time (EPT), and CO2 emission rates. As a result, it was found that the EPT is 1·5,2·5 years and the CO2 emission rate is 9,16,g-C/kWh. The generation cost was 11,12 US Cent/kWh on using 2 USD/W PV modules, and 19,20 US Cent/kWh on using 4 USD/W PV module price. Copyright © 2007 John Wiley & Sons, Ltd. [source] 8% Efficient thin-film polycrystalline-silicon solar cells based on aluminum- induced crystallization and thermal CVDPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2007I. Gordon Abstract A considerable cost reduction could be achieved in photovoltaics if efficient solar cells could be made from polycrystalline-silicon (pc-Si) thin films on inexpensive substrates. We recently showed promising solar cell results using pc-Si layers obtained by aluminum-induced crystallization (AIC) of amorphous silicon in combination with thermal chemical vapor deposition (CVD). To obtain highly efficient pc-Si solar cells, however, the material quality has to be optimized and cell processes different from those applied for standard bulk-Si solar cells have to be developed. In this work, we present the different process steps that we recently developed to enhance the efficiency of pc-Si solar cells on alumina substrates made by AIC in combination with thermal CVD. Our present pc-Si solar cell process yields cells in substrate configuration with efficiencies so far of up to 8·0%. Spin-on oxides are used to smoothen the alumina substrate surface to enhance the electronic quality of the absorber layers. The cells have heterojunction emitters consisting of thin a-Si layers that yield much higher Voc values than classical diffused emitters. Base and emitter contacts are on top of the cell in interdigitated finger patterns, leading to fill factors above 70%. The front surface of the cells is plasma textured to increase the current density. Our present pc-Si solar cell efficiency of 8% together with the fast progression that we have made over the last few years indicate the large potential of pc-Si solar cells based on the AIC seed layer approach. Copyright © 2007 John Wiley & Sons, Ltd. [source] Characterisation of rough reflecting substrates incorporated into thin-film silicon solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2006V. Terrazzoni Daudrix Abstract Four different categories of rough reflecting substrates as well as a single periodic grating are incorporated and tested within n-i-p type amorphous silicon (a-Si:H) solar cells. Each category is characterised by its own texture shape; dimensions were varied within the categories. Compared to flat reflecting substrates, gains in short-circuit current density (Jsc) up to 20% have been obtained on rough reflecting plastic substrates. As long as (1) the characteristic dimensions of the textures are lower than the involved light wavelengths, (2) the textures do not present any defects i.e. as long as they do not have large craters or bumps spread over the surface, the root mean square roughness (,RMS) as well as the ratio of average feature height to average period can be used to evaluate the gain in Jsc; if each category of randomly textured substrates is considered separately, the haze factor can be used to estimate ,RMS and thereby the gains in Jsc. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||