bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improving Polymer Based Photovoltaic Devices by Reducing the Voltage Loss at the Donor-Acceptor Interface
Authors: Moet Date J. D. , Slooff Lenneke H. , Kroon Jan M. , Chevtchenko Svetlana S. , Loos Joachim , Koetse Marc M. , Sweelssen Jorgen , Veenstra Sjoerd C. 
Published: April 2011

ABSTRACTThis paper discusses the characterization and optimization of organic solar cells based on a bulk heterojunction consisting of an alternating copolymer, containing a fluorene and a benzathiadiazole unit with two neighboring thiophene rings, and a fullerene derivative (PCBM). The resulting power conversion efficiency amounts 3.9±0.2 % (AM1.5, 100 mW/cm2) and these polymer solar cells are therefore considered auspicious for further research.
The Effect of Excess Carbon on the Crystallographic, Microstructural, and Mechanical Properties of CVD Silicon Carbide Fibers
Authors: Marzik James V , Croft William J. , Staples Richard J. , MoberlyChan Warren J. 
Published: April 2011

ABSTRACTSilicon carbide (SiC) fibers made by chemical vapor deposition (CVD) are of interest for organic, ceramic, and metal matrix composite materials due their high strength, high elastic modulus, and retention of mechanical properties at elevated processing and operating temperatures. The properties of SCS-6™ silicon carbide fibers, which are made by a commercial process and consist largely of stoichiometric SiC, were compared with an experimental carbon-rich CVD SiC fiber, to which excess carbon was added during the CVD process. The concentration, homogeneity, and distribution of carbon were measured using energy dispersive x-ray spectroscopy (SEM/EDS). The effect of excess carbon on the tensile strength, elastic modulus, and the crystallographic and microstructural properties of CVD silicon carbide fibers was investigated using tensile testing, x-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
Metastable Defects in Tritiated Amorphous Silicon
Authors: Ju Tong , Whitaker Janica , Zukotynski Stefan , Kherani Nazir , Taylor P. Craig , Stradins Paul 
Published: April 2011

AbstractThe appearance of optically or electrically induced defects in hydrogenated amorphous silicon (a-Si:H), especially those that contribute to the Staebler-Wronski effect, has been the topic of numerous studies, yet the mechanism of defect creation and annealing is far from clarified. We have been observing the growth of defects caused by tritium decay in tritiated a Si-H instead of inducing defects optically. Tritium decays to 3He, emitting a beta particle (average energy of 5.7 keV) and an antineutrino. This reaction has a half âlife of 12.5 years. In these 7 at.% tritium-doped a-Si:H samples each beta decay will create a defect by converting a bonded tritium to an interstitial helium, leaving behind a silicon dangling bond. We use ESR (electron spin resonance) and PDS( photothermal deflection spectroscopy) to track the defects. First we annealed these samples, and then we used ESR to determine the initial defect density around 1016 to 1017 /cm3 , which is mostly a surface spin density. After that we have kept the samples in liquid nitrogen for almost two years. During the two years we have used ESR to track the defect densities of the samples. The defect density increases without saturation to a value of 3x1019/cm3 after two years, a number smaller than one would expect if each tritium decay were to create a silicon dangling bond (2x1020/cm3). This result suggests that there might be either an annealing process that remains at liquid nitrogen temperature, or tritium decay in clustered phase not producing a dangling bond due to bond reconstruction and emission of the hydrogen previously paired to Si-bonded tritium atom. After storage in liquid nitrogen for two years, we have annealed the samples. We have stepwise annealed one sample at temperatures up to 200°C, where all of the defects from beta decay are annealed out, and reconstructed the annealing energy distribution. The second sample, which was grown at 150°C, has been isothermally annealing at 300 K for several months. The defects remain well above their saturation value at 300 K, and the shape of decay suggests some interaction between the defects.
Effects of Nitrogen Addition on the Properties of a-SiCN:H Films Using Hexamethyldisilazane
Authors: Limmanee Amornrat , Otsubo Michio , Sugiura Tsutomu , Sato Takehiko , Miyajima Shinsuke , Yamada Akira , Konagai Makoto 
Published: April 2011

AbstractWe deposited a-SiCN:H films by HWCVD using a gas mixture of hexamethyldisilazane, H2 and N2, and fabricated cast polycrystalline silicon solar cells with the a-SiCN:H passivation and anti-reflection layer. N2 addition led to the reduction of the refractive index of the a-SiCN:H films due to the increase in nitrogen concentration of the films. This improved performance of the antireflection layer. The advantage of adding N2 to the process was demonstrated by the improvement in short circuit current (JSC) and efficiency of cast polycrystalline silicon solar cells. At present, the efficiency of cast polycrystalline silicon solar cell using a-SiCN:H film as a passivation layer reached 14.2%.
Crystalline Silicon Surface Passivation by Pecv-Deposited Hydrogenated Amorphous Silicon Oxide Films [a-SiOx:H]
Authors: Mueller Thomas , Duengen Wolfgang , Job Reinhart , Scherff Maximilian , Fahrner Wolfgang 
Published: April 2011

AbstractIn the research field of crystalline silicon (c-Si) solar cells, electronic surface passivation has been recognized as a crucial step to achieve high conversion efficiencies. The main issue of this article is to analyze the surface passivation properties of both, n-type and p-type crystalline silicon wafers by hydrogenated amorphous silicon sub oxide [a-SiOx:H] films the for use in hetero-junction (a-Si/c-Si) solar cells. A window layer is obtained with a certain fraction of oxygen in the a-SiOx:H layers.The a-SiOx:H films were deposited by decomposition of silane, carbon dioxide and hydrogen as source gases using plasma enhanced chemical vapor deposition (PECVD). Films with varying deposition parameters such as gas flow ratio (oxygen fraction) and plasma frequency (13.56, 70.0 and 110.0 MHz) are compared.To determine the passivation quality of the a-SiOx:H films, microwave-detected photo conductance decay (µ-PCD) provides a contactless measurement of the effective recombination lifetime of free carriers. The film compositions and also the changes in the microscopic structure of the amorphous network upon thermal annealing are studied using Raman spectroscopy and optical profiling techniques.The Raman spectra reveal the generation of Si-(OH)x and Si-O-Si bonds after thermal annealing in the layers, leading to a higher effective lifetime, as it reduces the defect absorption of the sub oxides.For n-type FZ material, lifetime values as high as 1650 µs are obtained, resulting in a surface recombination velocity Seff < 9.5 cm/s.
Characterization of Silicon Carbide Thin Films Obtained Via Sublimation of a Solid Polymer Source Using Polymer-Source CVD Process
Authors: Oulachgar El Hassane , Aktik Cetin , Dostie Starr , Gujrathi Subhash , Scarlete Mihai 
Published: April 2011

AbstractSilicon carbide thin films have been deposited via sublimation of a solid organosilane polymer source using atmospheric pressure chemical vapour deposition process (PS-CVD). The advantages of this new process include high deposition rate, compatibility with batch process, hazard-free working environment and low deposition cost. The silicon carbide (SiC) thin films obtained through this process exhibit a highly uniform film thickness, highly conformal coating, and very high chemical resistance to acids and alkalis solutions. These proven characteristics make the SiC thin films obtained by PSCVD process very attractive as a structural material for micro-electro-mechanical systems (MEMS) and as a coating film in a wide range of other applications. These SiC thin films are also expected to be attractive as a semiconductor material provided that the defects and oxygen contamination can be reduced and efficiently controlled. In this work we have investigated the chemical, structural, electrical and optical properties of these films, using elastic recoil detection (ERD), Fourier transform infrared (FTIR) spectroscopy, photospectroscopy, ellipsometry, and capacitance-voltage measurements.
ESR Study of Crystallization of Hydrogenated Amorphous Silicon Thin Films
Authors: Su Tining , Ju Tong , Taylor P. Craig , Stradins Pauls , Xu Yueqin , Hasoon Falah , Wang Qi , Harrison Walter A. 
Published: April 2011

AbstractSolid-phase crystallization and the subsequent re-hydrogenation of the amorphous silicon thin films provides a low cost approach for thin-film crystalline Si:H-based photovoltaic devices. During the hydrogen effusion, significant lattice reconstruction occurs, as hydrogen is driven out of the film, accompanied by creation and migration of a large number of dangling bonds. We used electron-spin-resonance (ESR) to study evolution of the local order surrounding these dangling bonds during crystallization. When samples made by both plasma enhanced chemical vapor deposition (PECVD) and the and hot wire CVD (HWCVD) are heated to 560°C, hydrogen effuses within 30 min, giving rise to H-effused defect densities of about 5x1018 cm-3. Further heating at 560°C results in crystallizati°n in the HWCVD sample after about 200 min. On the other hand, PECVD samples crystallize only when heated up to 580°C, and then only after much longer times (Dt ~ 1300 min) [1,2]. ESR defects in both samples persist at the 5x1018 cm-3 level as long as the sample remains amorphous during the grain nucleation period. As the crystallites appear, the defect densities gradually decrease and saturate at about 3x1017 cm-3 as the crystallization is completed, both in HWCVD and PECVD samples.In the H-effused states before crystallization, the ESR signals for both the HWCVD and PECVD samples show significant exchange-narrowing, suggesting that the defects are probably clustered. As the sample crystallizes, the defect clustering largely disappears, yet the line-widths in fully crystallized films are somewhat narrower than those in typical micro-crystalline silicon thin films as reported earlier [3]. This difference is probably due the specific structures of the grain boundaries in the present study. The effect of re-hydrogenation on both the H-effused amorphous and crystallized states will be discussed.
Relation between Electronic Properties and Density of Crystalline Agglomerates in Microcrystalline Silicon
Authors: Bronsveld Paula C.P. , Verkerk Arjan , Mates Tomas , Fejfar Antonin , Rath Jatindra K. , Schropp Ruud E.I. 
Published: April 2011

AbstractA series of silicon thin films was made by very high frequency plasma enhanced chemical vapour deposition (VHF PECVD) at substrate temperatures below 100 °C at different hydrogen to silane dilution ratios. The electronic properties of these layers were studied as a function of the surface crystalline fraction as determined accurately from a combination of microscope images at different length scales (gathered by using different types of microscopes). The results show that the electrical conductivity increases monotonously as a function of crystalline surface coverage and no discontinuity is observed at the percolation threshold. An increase in conductivity of four orders of magnitude for layers with a high crystalline content is observed after annealing at temperatures up to 170 °C. Combined with the information that oxygen is incorporated at Si-H surface bond sites, this suggests that doping of the intergrain boundaries by oxygen might be dominantly responsible for the electronic properties of mixed phase silicon.
Flexible a-Si:H-based Image Sensors Fabricated by Digital Lithography
Authors: Wong William S. , Ng TseNga , Chabinyc Michael L. , Lujan Rene A. , Apte Raj B. , Sambandan Sanjiv , Limb Scott , Street Robert A. 
Published: April 2011

AbstractAmorphous silicon-based x-ray image sensor arrays were fabricated on poly-ethylene naphthalate substrates at process temperatures below 180°C. Patterning of the thin-film transistor backplane was accomplished using ink-jet printed etch masks. The sensor devices were found to be comparable to high-temperature processed devices. The integration of the sensor stack, TFT array and PEN substrate resulted in a flexible x-ray image sensor with 180×180 pixels with 75 dpi resolution.
Transient Current Behavior of Vertically Integrated Amorphous Silicon Diodes
Authors: Choong Gregory , Wyrsch Nicolas , Ballif Christophe , Kaufmann Rolf , Lustenberger Felix 
Published: April 2011

AbstractMonolithic image sensors based on Thin Film on CMOS (TFC) Technology are becoming more and more attractive as an alternative solution to conventional active pixel sensors (APS). Imager with high sensitivity, high dynamic coupled with low dark current values (10-100 pA/cm2 @ 104 V/cm) have been developed. However, issues such as light-induced degradation and image lag hinder the commercial development of a-Si:H based image sensors. The problem of image lag is caused by residual current due to the release of trapped charges after the switch off of the illumination.In this paper, we present a comprehensive study of the transient behavior of the photocurrent in a-Si:H photodiodes deposited on glass, as well as in corresponding diodes implemented in a TFC image sensor when illumination is switched off or periodically varied. The influence of the pixel architecture for two different cases is also analyzed: One setup reproduces the typical 3 transisor APS pixel architecture behavior, in which the bias voltage of the diode varies with the photogenerated charge while the second setup keeps a constant bias voltage applied to the diode by using a charge integrator.The influence of the light-induced defect creation on the performance of the sensors is also presented and discussed.
Resistive Losses at c-Si/a-Si:H/ZnO Contacts for Heterojunction Solar Cells
Authors: Einsele Florian , Rostan Phillip Johannes , Rau Uwe 
Published: April 2011

AbstractWe study resistive losses at (p)c-Si/(p)Si:H/(n)ZnO heterojunction back contacts for high efficiency silicon solar cells. We find that a low tunnelling resistance for the (p)a-Si:H/(n)ZnO part of the junction requires deposition of Si:H with a high hydrogen dilution RH > 40 resulting in a highly doped μc-Si:H layer. Such a μc-Si:H layer if deposited directly on a Si wafer yields a surface recombination velocity of S  180 cm/s. Using the same layer as part of a (p)c-Si/(p)Si:H/(n)ZnO back contact in a solar cell results in an open circuit voltage Voc = 640 mV and a fill factor FF = 80 %. Insertion of an (i)a-Si-layer between the μc-Si:H and the wafer leads to a further decrease of S and, for the solar cells to an increase of VOC. However, if the thickness of this intrinsic layer exceeds a threshold of 3 nm, resistive losses lead to a degradation of the fill factor of the solar cells. These resistive losses result from a valence band offset δEV between a-Si:H and c-Si of about 600 meV. The fill factor losses overcompensate the VOC gain such that there is no benefit of the (i)a-Si:H interlayer for the overall solar cell performance when using an (i)a-Si:H/(p)uc-Si:H double layer.
Photocurrent Profile in a-SiC:H Monolithic Tandem Pinpin and Pinip Photodiodes
Authors: Fantoni Alessandro , Vieira Manuela , Vygranenko Yuri 
Published: April 2011

AbstractWe present in this paper results about the analysis of photocurrent and spectral response in a-SiC:H/ a-Si:H pinpin and pinip structures. Our experiments and analysis reveal the photocurrent profile to have a strong nonlinear dependence on the externally applied bias and on the light absorption profile, i.e. on the incident light wavelength and intensity. Our interpretation points out the cause of such effect to a self biasing of the junctions under certain unbalanced light generation of carriers and to an asymmetric reaction of the internal electric fields to the externally imposed bias. The possibility to relate such a behavior to the light intensity and wavelength indicates realistic hypothesis of using these structures and this effect for color recognition sensors.We present results about the experimental characterization of the structures and numerical simulations obtained with the program ASCA. Considerations about electrical field profiles and inversion layers will be taken into account to explain the optical and voltage bias dependence of the spectral response. Our results show that in both structures the application of an external electrical bias (forward or reverse) mainly influences the field distribution within the less photo excited sub-cell.
Temperature Dependence of Leakage Current in Segmented a-Si:H n-i-p Photodiodes
Authors: Chang Jeff Hsin , Chuang Tsu Chiang , Vygranenko Yuri , Striakhilev Denis , Kim Kyung Ho , Nathan Arokia , Heiler Gregory , Tredwell Timothy 
Published: April 2011

AbstractHydrogenated amorphous silicon (a-Si:H) n-i-p photodiodes may be used as the pixel sensor element in large-area array imagers for medical diagnostics applications. The dark current level is an important parameter that dictates the performances of these types of pixelated imaging devices. Through measurements performed at different ambient temperatures, the leakage current components of segmented a-Si:H n-i-p photodiodes were extracted and analyzed. It was found that the central component of the reverse current depends exponentially on bias and temperature. The activation energy of this component is independent of bias. The peripheral component of reverse current exhibits linear bias dependence at temperatures up to 50°C, while the contribution of this component diminishes at high temperatures. The dependence of dark current components on bias and temperature could be described by compact analytical equations. The model of forward and reverse dark current characteristics in temperature range was implemented in Verilog-A hardware description language.
Structural Analysis of Nanocrystalline Silicon Prepared by Hot-wire Chemical Vapor Deposition on Polymer Substrates
Authors: Adachi Michael Musashi , Taghibakhsh Farhad , Kavanagh Karen L. , Karim Karim S. 
Published: April 2011

AbstractNanocrystalline silicon (nc-Si:H) films were deposited by hot-wire chemical vapor deposition (HWCVD) directly onto Corning glass and polyimide (Kapton E) substrates. The effect of silane concentration (in hydrogen carrier gas) on film crystallinity and conductivity were studied for a constant substrate growth temperature of 220°C. Raman spectroscopy, X-ray diffraction and cross-sectional transmission electron microscopy (XTEM) showed that nc-Si:H (grain-size 20-65 nm) was observed for silane concentrations below 5.8 %. Similar to previous reports, closer inspection using XTEM found that there was an initial growth of an amorphous interfacial layer which then crystallized into a randomly-oriented polycrystalline material after 10 - 100 nm of growth.. However, unlike previous reports, there was no detectable difference in the structure or conductivity for films grown on the two types of substrates. In both cases, the dark conductivity decreased with increasing silane concentration while the photo-conductivity was uniform for all films at values between 2 and 4×10-5 S/cm.
Manipulating the Hydrogen-Bonding Configuration in ETP-CVD a-Si:H
Authors: Wank Michael , van Swaaij R. A. C. M. M. , van de Sanden M. C. M. 
Published: April 2011

AbstractThe effect of ion bombardment on the relationship between the critical hydrogen concentration and the reactor pressure has been investigated for hydrogenated amorphous silicon (a-Si:H) deposited with the expanding thermal plasma-CVD (ETP-CVD) method. By changing the reactor pressure the ionic cluster formation in the plasma can be varied. It is observed that the decrease of the critical hydrogen concentration with increasing reactor pressure can not be compensated by ion bombardment at 14V biasing. Biasing with 20V however increases the critical hydrogen concentration nearly up to the value obtained at low pressures. This indicates that the incorporation of ionic cluster formed at elevated reactor pressures can be reduced by substrate biasing, possibly due to break-up upon impact on the substrate surface or due to processes occurring in the secondary plasma close to the substrate.
Materials Optimization for Silicon Heterojunction Solar Cells Using Spectroscopic Ellipsometry
Authors: Levi Dean , Iwanizcko Eugene , Johnston Steve , Wang Qi , Branz Howard M 
Published: April 2011

AbstractOur research team has used hot wire chemical vapor deposition (HWCVD) to fabricate silicon heterojunction (SHJ) solar cells on p-type FZ silicon substrates with efficiencies as high as 18.2%. The best cells are deposited on anisotropically-textured (100) silicon substrates where an etching process creates pyramidal facets with (111) crystal faces. Texturing increases Jsc through enhanced light trapping, yet our highest Voc devices are deposited on un-textured (100) substrates. One of the key factors in maximizing the efficiency of our SHJ devices is the process of optimization of the material properties of the 3 - 5 nm thick hydrogenated amorphous silicon (a-Si:H) layers used to create the junction and back contact in these cells. Such optimization is technically challenging because of the difficulty in measuring the properties of extremely thin layers. This difficulty is compounded by the fact that the properties of such amorphous layers are substrate- and thickness-dependent. In this study, we have utilized spectroscopic ellipsometry (SE) and photoconductivity decay to conclude that a-Si:H films grown on (111) substrates are substantially similar to films grown on (100) substrates. In addition, analysis of the substrate temperature dependence of surface roughness evolution reveals a substrate-independent mechanism of surface smoothening with an activation energy of 0.28 eV. Analysis of the substrate temperature dependence of surface passivation reveals a passivation mechanism with an activation energy of 0.63 eV.
Surface Chemical Characteristics of CMP Polyurethane Pads
Authors: Xiang Hongqi , Prasad Abaneshwar , Remsen Edward E. 
Published: April 2011

ABSTRACTAttenuated total reflection FT-IR spectroscopy coupled with a hydrogen-deuterium exchange technique is employed to investigate the surface chemistry of two polishing pads, a thermoplastic polyurethane (TPU) pad and a commercial cast urethane (PU) pad. A time/temperature-dependent reduction of nitrogen-hydrogen stretching modes (νN-H) was observed when the pads were immersed in deuterium oxide (D2O). Compared to TPU pads, the PU pads showed an ambiguous correlation between dependence of the band intensity changes and D2O-immersion time/temperature. For both types of pads, a sharp decrease in νN-H band intensity and an unexpected rebound in νN-H band intensity were observed within 24 hrs after immersing the pads in D2O. However, a comparable rebound in νN-H band intensity was not observed for conditioned TPU pad samples. This phenomenon is proposed to be due to a rearrangement of polar groups at the pad surface when the pad is immersed in water, which may influence pad performance on the asperity level.