bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrogenated Amorphous Silicon Based Solar Cells: Optimization Formalism and Numerical Algorithm
Authors: Shkrebtii Anatoli , Kryuchenko Yuriy , Sachenko Anaroliy , Sokolovskyi Igor , Gaspari Franco 
Published: June 2009

AbstractThin film hydrogenated amorphous silicon (a-Si:H) is widely used in photovoltaics. In order to get the best possible performance of the a-Si:H solar cells it is important to optimize the amorphous film and solar cells in terms their parameters such as mobility gap,p-,i- andn-layer doping levels, electron and hole lifetime and their mobilities, resistance of p-, i- and n-layers, contact grid geometry and parameters of the transparent conducting and antireflecting layers, and others. To maximize thin a-Si:H film based solar cell performance we have developed a general numerical formalism of photoconversion, which takes into account all the above parameters for the optimization. Application of the formalism is demonstrated for typical a-Si:H based solar cells before Staebler-Wronski (SW) light soaking effect. This general formalism is not limited to a-Si:H based systems only, and it can be applied to other types of solar cells as well.
Junction Capacitance Study of a-SiGe:H Solar Cells Grown at Varying RF and VHF Deposition Rates
Authors: Hugger Peter G. , Lee JinWoo , Cohen David J. , Yue Guozhen , Xu Xixiang , Yan Baojie , Yang Jeff , Guha Subhendu 
Published: June 2009

AbstractSignificant advances have been made in increasing the deposition rate of hydrogenated silicon germanium alloys (a-SiGe:H) using a modified VHF glow discharge deposition method while also maintaining good electronic properties important for its application in photovoltaic devices. We examine the electrical and optical properties of these alloys deposited either by RF (13.56MHz) or the modified VHF methods over deposition rates varying from 1 to 10 Å/s. The electronic properties of a series of 1.4 eV optical gap a-SiGe:H i-layers, in many cases in solar cell device configurations, were characterized. Drive-level capacitance profiling was used to determine the deep defect densities, and transient photocapacitance measurements allowed us to determine the Urbach energies. Results were obtained for both the annealed and light-soaked degraded states and these results were correlated to the cell performance parameters. In general the a-SiGe:H layers deposited using the modified VHF excitation exhibited improved electronic properties at higher growth rates than the RF deposited samples.
Passivation of Silicon Surfaces Using Atomic Layer Deposited Metal Oxides
Authors: Wang Jun , Farrokh Baroughi Mahdi , Shanmugam Mariyappan , Samadzadeh-Tarighat Roohollah , Sivoththaman Siva , Paul Sanjoy 
Published: June 2009

AbstractSurface passivation of silicon substrates using atomic layer deposited Al2O3 and HfO2 thin films are assessed. Al2O3 and HfO2 dielectric layers with various thicknesses were deposited on both sides of n-type (100) FZ-Si substrates (resistivity 4 – 6 Ω-cm) at 200°C by atomic layer deposition (ALD) system. The effective excess carrier lifetime of as-deposited oxide/Si/oxide structure was measured by microwave-photoconductivity-decay (MWPCD) measurement technique and it was observed that the thicker ALD dielectrics lead to higher effective excess carrier lifetime and better surface passivation. The measurements showed average excess carrier lifetime values of 302 μs and 347 μs for as-deposited Al2O3 and HfO2 passivated Si substrates with 150 ALD cycles, respectively. MWPCD and capacitance-voltage (C-V) measurements suggest that as-deposited ALD HfO2 layer leads to a better surface passivation compared to as-deposited ALD Al2O3 layer. Further, the results suggest that there exist fixed negative charges in the bulk of the ALD dielectrics and this contributes to the field effect passivation of the silicon surfaces.
Highly Transparent and High Haze ZnO:Al film For Front TCO of a-Si:H and μc-Si:H Solar Cells by Controlling Oxygen Flow
Authors: Kang Dong-Won , Kuk Seung-Hee , Ji Kwang-Sun , Ahn Seh-Won , Han Min-Koo 
Published: June 2009

AbstractWe fabricated highly transparent and high haze ZnO:Al film for front TCO of amorphous and microcrystalline silicon solar cells. We have sputtered ZnO:Al film of 1.3 μm on the thin seed layer of about 60nm which was previously sputtered on the glass substrate by using 4% dilution of oxygen to argon gas. The ZnO:Al film grown on the seed layer had much higher crystalline phase than one without any seed layer. Our bi-layer ZnO:Al film showed low resistivity of 2.66×10-4 Ω•cm and sheet resistance of 2.08 Ω/⇐ while conventional ZnO:Al film showed resistivity of 3.24×10-4 Ω•cm and sheet resistance of 2.46 Ω/⇐. After surface texturing by 0.5% HCl wet-chemical etching, the transmittance of ZnO:Al film was increased from 83.7% to 88.1% at wavelength of 550nm through the seed layer. Also the transmittance at 800nm was increased from 82.3% to 88.9%. Especially, haze values of the ZnO:Al film were drastically increased from 58.7% to 90.6% at wavelength of 550nm by employing the seed layer. Also haze values at 800nm were increased from 22.1% to 68.1%. It is expected that the seed layer method to improve the quality of ZnO:Al film will contribute to an increase of solar cell efficiency due to the high capability of light trapping and low electrical resistivity.
Optics in Thin-film Silicon Solar Cells with Integrated Lamellar Gratings
Authors: Dewan Rahul , Madzharov Darin , Raykov Andrey , Knipp Dietmar 
Published: June 2009

AbstractLight trapping in microcrystalline silicon thin-film solar cells with integrated lamellar gratings was investigated. The influence of the grating dimensions on the short circuit current and quantum efficiency was investigated by numerical simulation of Maxwell’s equations by a Finite Difference Time Domain approach. For the red and infrared part of the optical spectrum, the grating structure leads to scattering and higher order diffraction resulting in an increased absorption of the incident light in the silicon thin-film solar cell. By studying the diffracted waves arising from lamellar gratings, simple design rules for optimal grating dimensions were derived.
Voltage Controlled Amorphous Si/SiC Phototransistors and Photodiodes as Wavelength Selective Devices: Theoretical and Electrical Approaches
Authors: Vieira Manuel Augusto , Vieira Manuela , Louro Paula , Fernandes Miguel , Fantoni Alessandro , Barata Manuel 
Published: June 2009

AbstractIn this paper single and stacked structures that can be used as wavelength selective devices, in the visible range, are analysed. Two terminal heterojunctions ranging from p-ií-n to p-i-n-p-i’-n configurations are studied. Three terminals double staked junctions with transparent contacts in-between are also considered to increase wavelength discrimination. The color discrimination was achieved by ac photocurrent measurement under different externally applied bias. Experimental data on spectral response analysis and current –voltage characteristics are reported.
A theoretical analysis and an electrical simulation procedure are performed to support the wavelength selective behaviour. Good agreement between experimental and simulated data was achieved. Results show that in the single p-i-n configuration the device acts mainly as an optical switch while in the double ones, due to the self bias effect, the input channels are selectively tuned by shifting between positive and negative bias. If the internal terminal is used the inter-wavelength cross talk is reduced and the S/N increased.
Photoelectron Spectroscopy Measurements of Valence Band Discontinuities for a-Si:H/c-Si Heterojunction Solar Cells
Authors: Kaneko Tetsuya , Kondo Michio 
Published: June 2009

AbstractThe valence band discontinuity (offset) between a-Si:H-based intrinsic thin layers and c-Si substrates was estimated using ultraviolet photoelectron spectroscopy (UPS) in combination with x-ray photoelectron spectroscopy (XPS). A core level shift measured by XPS was utilized to correct the shifts of UPS spectra after UV light illumination. Thin films of a-Si:H, a-SiO:H and a-SiC:H were prepared by plasma-enhanced chemical vapor deposition (PECVD) using SiH4, CO2 and CH4 gases. The valence band offset of 0.11 eV was obtained from the a-Si:H/c-Si heterojunction, whereas 0.27 eV was obtained from the a-SiO:H/c-Si heterojunction. Moreover, the valence band offset between the c-Si and the a-SiC:H deposited with [CH4]=10 SCCM and [CH4]=20 SCCM were determined to be 0.25 eV and 0.36 eV, respectively. The c-Si-based heterojunction solar cells with estimated i layer in this study were fabricated, reduction of FF with increasing the valence band offset was observed. It is likely that increasing of the valence band offset contributes to the reduction of FF.
High efficiency amorphous and nanocrystalline silicon based multi-junction solar cells deposited at high rates on textured Ag/ZnO back reflectors
Authors: Yue Guozhen , Sivec Laura , Yan Baojie , Yang Jeff , Guha Subhendu 
Published: June 2009

AbstractWe report our recent progress on nc-Si:H single-junction and a-Si:H/nc-Si:H/nc-Si:H triple-junction cells made by a modified very-high-frequency (MVHF) technique at deposition rates of 10-15 Å/s. First, we studied the effect of substrate texture on the nc-Si:H single-junction solar cell performance. We found that nc-Si:H single-junction cells made on bare stainless steel (SS) have a good fill factor (FF) of ˜0.73, while it decreased to ˜0.65 when the cells were deposited on textured Ag/ZnO back reflectors. The open-circuit voltage (Voc) also decreased. We used dark current-voltage (J-V), Raman, and X-ray diffraction (XRD) measurements to characterize the material properties. The dark J-V measurement showed that the reverse saturated current was increased by a factor of ˜30 when a textured Ag/ZnO back reflector was used. Raman results revealed that the nc-Si:H intrinsic layers in the two solar cells have similar crystallinity. However, they showed a different crystallographic orientation as indicated in XRD patterns. The material grown on Ag/ZnO has more random orientation than that on SS. These experimental results suggested that the deterioration of FF in nc-Si:H solar cells on textured Ag/ZnO was caused by poor nc-Si:H quality. Based on this study, we have improved our Ag/ZnO back reflector and the quality of nc-Si:H component cells and achieved an initial and stable active-area efficiencies of 13.4% and 12.1%, respectively, in an a-Si:H/nc-Si:H/nc-Si:H triple-junction cell.
Microcrystalline Silicon Thin-Film Transistors for Ambipolar and CMOS Inverters
Authors: Chan Kah-Yoong , Gordijn Aad , Stiebig Helmut , Knipp Dietmar 
Published: June 2009

AbstractMicrocrystalline silicon (μc-Si:H) thin-film transistors (TFTs) have lately gained much attention due to their high charge carrier mobilities. We report on top-gate μc-Si:H TFTs fabricated by plasma-enhanced chemical vapor deposition at process temperatures below 180 °C with high electron and hole charge carrier mobilities exceeding 50 cm2/Vs and 12 cm2/Vs, respectively. Based on the μc-Si:H TFTs different thin-film inverters were realized including ambipolar and complimentary metal-oxide-semiconductor (CMOS) inverters. Microcrystalline CMOS inverters exhibit high voltage gains exceeding 22, whereas ambipolar inverters show reduced voltage gains of 10 at low operating voltages. The electrical characteristics of the μc-Si:H CMOS and ambipolar thin-film inverters will be discussed in terms of the voltage transfer curve, the voltage gain and the power dissipation.
Carrier drift-mobilities and solar cell models for amorphous and nanocrystalline silicon
Authors: Schiff Eric A 
Published: June 2009

AbstractHole drift mobilities in hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) are in the range of 10-3 to 1 cm2/Vs at room-temperature. These low drift mobilities establish corresponding hole mobility limits to the power generation and useful thicknesses of the solar cells. The properties of as-deposited a-Si:H nip solar cells are close to their hole mobility limit, but the corresponding limit has not been examined for nc-Si:H solar cells. We explore the predictions for nc-Si:H solar cells based on parameters and values estimated from hole drift-mobility and related measurements. The indicate that the hole mobility limit for nc-Si:H cells corresponds to an optimum intrinsic-layer thickness of 2-3 μm, whereas the best nc-Si:H solar cells (10% conversion efficiency) have thicknesses around 2 μm.
Bulk-heterojunction Based on Blending of Red and Blue Luminescent Silicon Nanocrystals and P3HT Polymer
Authors: Švrček Vladimir , Kondo Michio 
Published: June 2009

AbstractBlending of red and blue photoluminescent silicon nanocrystals (Si-ncs) with poly(3-hexylthiophene (P3HT) conjugated polymer is demonstrated. The room temperature luminescent and ambient conditions stable Si-ncs prepared by electrochemical etching and laser ablation in water are used for the blend fabrication. Furthermore photo-electric properties in parallel configuration on platinum interdugitated contact are shown. Both types of Si-ncs results the bulk-heterojunction formation and photoconductivity is observed when the blends are irradiated AM1.5. The increase in photoconductivity is rather the same and ratio between photo- and dark-conductivity is about 1.7. The nanocrystal oxidation during laser ablation fabrication process in water hinders the transport properties of the blend.
Imaging Electron Transport across Grain Boundaries in an Integrated Electron and Atomic Force Microscopy Platform: Application to Polycrystalline Silicon Solar Cells
Authors: Romero Manuel J , Liu Fude , Kunz Oliver , Wong Johnson , Jiang Chun-Sheng , Al-Jassim Mowafak , Aberle Armin G 
Published: June 2009

AbstractWe have investigated the local electron transport in polycrystalline silicon (pc-Si) thin-films by atomic force microscopy (AFM)-based measurements of the electron-beam-induced current (EBIC). EVA solar cells are produced at UNSW by <i>EVAporation</i> of a-Si and subsequent <i>solid-phase crystallization</i>–a potentially cost-effective approach to the production of pc-Si photovoltaics. A fundamental understanding of the electron transport in these pc-Si thin films is of prime importance to address the factors limiting the efficiency of EVA solar cells. EBIC measurements performed in combination with an AFM integrated inside an electron microscope can resolve the electron transport across individual grain boundaries. AFM-EBIC reveals that most grain boundaries present a high energy barrier to the transport of electrons for both p-type and n-type EVA thin-films. Furthermore, for p-type EVA pc-Si, in contrast with n-type, charged grain boundaries are seen. Recombination at grain boundaries seems to be the dominant factor limiting the efficiency of these pc-Si solar cells.
Blue/White Emission from Hydrogenated Amorphous Silicon Carbide Films Prepared by PECVD
Authors: Ivashchenko Volodymyr , Vasin Andrey , Ivashchenko L. A. , Skrynskyy P. L. 
Published: June 2009

AbstractPhotoluminescence (PL) from hydrogenated silicon carbide (SiC:H) films is studied at room temperature. The films were deposited by plasma-enhanced chemical vapor (PECVD) technique with and without substrate bias using methyltrichlorosilane as a main precursor. After the deposition the samples were annealed at various temperatures in vacuum. The films were characterized by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The samples deposited without substrate bias (series A) were amorphous, whereas the samples deposited with negative substrate bias -100V (series B) were nanocrystalline. The one-peak (470 nm) and double-peak (415 and 437 nm) PL structures of the as-deposited samples A and B were observed, respectively. Annealing strongly enhanced intensity of PL of the samples B and trandformed PL spectrum from double-peak into broad featureless band with intensity at about 470 nm. The blue PL in as-deposited films B is supposed to be assigned to the radiative recombination in the sites located at the nanocrystallite surface, whereas the photo excitation of carries mostly occurs in nanocrystallite cores. A further increase in annealing temperature causes hydrogen effusion, which leads to an increase of the concentration of non-raidative recombination centers associated with dangling-bonds and as a result, to the quenching of PL.
Characterization of Microcrystalline Silicon by High Wavenumber Raman Scattering
Authors: Johnson Erik V , Kroely Laurent , Moreno Mario , Roca i Cabarrocas Pere 
Published: June 2009

AbstractOne of the primary challenges in the application of hydrogenated microcrystalline silicon (μc-Si:H) to photovoltaic cells is achieving high growth rates while maintaining good material quality over a wide process window. The rapid characterization of the material without generating a complete cell is thus a useful tool to determine said process window. Infrared absorption due to the various vibrational modes of the material has been used as a coarse tool towards this purpose, but the use of FTIR to perform this diagnosis limits the substrates upon which the analysis can be performed. We report on the use of high wave-number (1800-2200 cm-1) Raman scattering to perform a similar role of telltale peak detection directly on solar cells and on substrates suitable for thin-film photovoltaics. We evaluate material grown from SiF4 by RF-PECVD and from SiH4 by Matrix Distributed Electron Cyclotron Resonance (MDECR-) PECVD.
Properties of Nano-crystalline Silicon-Carbide Films Prepared Using Modulated RF- PECVD
Authors: Zhu Feng , Hu Jian , Matulionis Ilvydas , Kunrath Augusto , Madan Arun 
Published: June 2009

AbstractWe report on the fabrication of nano-crystalline silicon-carbide (nc-SiC) using pulse modulated RF-PECVD technique, from silane (SiH4) and methane (CH4) gas mixtures which is highly diluted in hydrogen (H2). The microstructure of nc-SiC material is nanometer-size silicon crystallites embedded in amorphous silicon-carbide (a-SiC) matrix. As carbon incorporation in nc-Si film increases, the bandgap is enlarged from 1.1eV to 1.55eV as measured by Photothermal Deflection Spectroscopy (PDS) while the crystalline volume fraction decreases from 70% to about 20%. It is found that the crystalline volume fraction, grain size and dark conductivity of nc-SiC films can be enhanced with applying a negative DC bias to substrate during deposition.
Ion Assisted ETP-CVD a-Si:H at Well Defined Ion Energies
Authors: Wank Michael A. , van Swaaij René , van de Sanden M. 
Published: June 2009

AbstractHydrogenated amorphous silicon (a-Si:H) was deposited with the Expanding Thermal Plasma-CVD (ETP CVD) method utilizing pulse-shaped substrate biasing to induce controlled ion bombardment during film growth. The films are analyzed with in-situ real time spectroscopic ellispometry, FTIR spectroscopy, as well as reflection-transmission and Fourier transform photocurrent spectroscopy (FTPS) measurements. The aim of this work is to investigate the effect ion bombardment with well defined energy on the roughness evolution of the film and the material properties.We observe two separate energy regimes with material densification and relatively constant defect density below ˜ 120-130 eV and a constant material density at increasing defect density > 120-130 eV substrate bias. We discuss our results in terms of possible ion – surface atom interactions and relate our observations to reports in literature.
Phosphorus and Boron Doping Effect on Nanocrystalline Formation in Hydrogenated Amorphous and Nanocrystalline Mixed-phase Silicon Thin Films
Authors: Jiang Chunsheng , Yan Yanfa , Moutinho Helio R. , Al-Jassim Mowafak , Yan Baojie , Sivec Laura , Yang Jeff , Guha Subhendu 
Published: June 2009

AbstractPhosphorus and Boron doping effects on the microstructure of nanocrystallites in hydrogenated amorphous and nanocrystalline mixed-phase silicon films were investigated using Raman spectroscopy, secondary ion mass spectrometry, cross-sectional transmission electron microscopy, atomic force microscopy, and conductive atomic force microscopy. The characterizations revealed the following observations. First, the mixed-phase Si:H films can be heavily doped in ˜1021/cm3 by adding PH3 and BF3 in the precursor gases. Second, the intrinsic and doped films can be made in a similar crystalline volume fraction by adjusting hydrogen dilution ratio. The hydrogen dilution ratio is much higher for P-doped films than for the intrinsic film with the similar crystallinity. Third, the doping impacts the nanostructures in the films significantly. Nanograins aggregate to form cone-shaped clusters in the intrinsic and B-doped films but isolate and randomly distribute in amorphous tissues in the P-doped films. The cones in the intrinsic and B-doped films are also different. The cone-angle is smaller and the nanograin density is lower in the B-doped films than in the intrinsic films. These P- and B-doping effects on the nanocrystalline formation are interpreted in terms of diffusions of Si-related radicals during the film growth.
Effects of a Bias Voltage During Hydrogenation on Passivation of the Defects in Polycrystalline Silicon for Solar Cells
Authors: Saito Yoji , Kohata Hayato , Sano Hideyuki 
Published: June 2009

AbstractThe short circuit current and conversion efficiency of the poly(multi)-crystalline solar cells are increased by the passivation process using hydrogen plasma. The passivation rate apparently increases at a reverse bias voltage near 0.6V during the hydrogenation process. The effects of the bias voltage on the passivation are large at the substrate temperatures between 200C and 250C. The phenomena are likely due to the existence of positively-ionized hydrogen, H+. The H+ ions can be accelerated from the surface into the bulk by the electric field with the negative bias. The possibility of the H+ ions in the bulk silicon has been predicted in the previous reports. The increase of the incorporated hydrogen is confirmed by IR absorption measurements. The enhanced diffusion of hydrogen induced by the reverse bias is supported by the results of spectral response characteristics of the hydrogenated solar cells.
Optical Processing Devices for Optical Communications: Multilayered a-SiC:H Architectures
Authors: Louro Paula , Vieira Manuela , Vieira M. A. , Fernandes Miguel , Fantoni Alessandro , Lavareda G. , Carvalho C. N. 
Published: June 2009

AbstractIn this paper three multilayered architectures based on a-SiC:H with voltage controlled spectral selectivity in the visible spectrum range are analyzed. Multiple simultaneous modulated communication channels (red, green and blue or their polychromatic mixtures) were transmitted together at different frequencies. The combined optical signal was analyzed by reading out the photocurrent signal generated by the devices, under different applied voltages. Results show that the multiplexed signal depends on the device architecture and is balanced by the wavelength and transmission speed of each input channel, keeping the memory of the incoming optical carriers. In the single graded p-i’i-n configuration the device acts mainly as an optical switch while in two stacked p-i’-n-(ITO)-p-i-n configurations, the input channels are selectively tuned by shifting between forward and reverse bias. An electrical model, supported by a numerical simulation gives insight into the device operation.
Evaluation of the Electrical Properties, Piezoresistivity and Noise of poly-SiGe for MEMS-above-CMOS applications
Authors: Gonzalez Pilar , Lenci Silvia , Haspeslagh Luc , De Meyer Kristin , Witvrouw Ann 
Published: June 2009

AbstractIn this work, the electrical properties of heavily doped poly-SiGe deposited at temperatures compatible with MEMS integration on top of standard CMOS are reported. The properties studied are resistivity, temperature coefficient of resistance, noise, piezoresistivity, Hall mobility and effective carrier concentration. The obtained results prove the potential of using poly-SiGe as a sensing layer for MEMS-above-CMOS applications.