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S. De Wolf,
Y. Andrault,
L. Barraud, R. Bartlome,
D. Bätzner,
P. Bôle,
G. Choong,
B. Demaurex,
A. Descoeudres,
C. Guérin, [......],
M. Kobas,
D. Lachenal,
B. Mendes,
B. Strahm,
M. Tesfai,
G. Wahli,
F. Wuensch,
F. Zicarelli,
A. Buechel,
C. Ballif
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ABSTRACT: Silicon heterojunction technology (Si-HJT) consists of thin amorphous silicon layers on monocrystalline silicon wafers and allows for photovoltaic solar cells with energy-conversion efficiencies above 20%, also at industrial-production level. This article reports how this may be achieved. First, we focus on the surface-passivation mechanism of intrinsic and doped amorphous silicon films in such solar cells, enabling record-high values for the open-circuit voltage. Next, the industrial upscaling in large-area reactors of such film deposition is discussed, including the fabrication of solar cells with energy-conversion efficiencies as high as 21%.
Solid-State and Integrated Circuit Technology (ICSICT), 2010 10th IEEE International Conference on; 12/2010
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ABSTRACT: We present two laser systems to monitor plasma conditions in a plasma-enhanced chemical vapor deposition chamber. The first optical system is a high-resolution quantum cascade laser-based infrared absorption spectrometer designed to measure the input silane depletion fraction (dissociation efficiency) and to determine the amorphous-to-microcrystalline silicon transition regime. The second optical system is a compact and low-cost laser light scattering device designed to detect the formation of powder particles. In the absence of such particles, the silane depletion fraction provides an in situ measurement of the film growth rate.
Photovoltaic Specialists Conference (PVSC), 2009 34th IEEE; 07/2009
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ABSTRACT: The silane dissociation efficiency, or depletion fraction, is an important plasma parameter by means of which the film growth rate and the amorphous-to-microcrystalline silicon transition regime can be monitored in situ. In this letter we implement a homebuilt quantum cascade laser-based absorption spectrometer to measure the silane dissociation efficiency in an industrial plasma-enhanced chemical vapor deposition system. This infrared laser-based diagnostic technique is compact, sensitive, and nonintrusive. Its resolution is good enough to resolve Doppler-broadened rotovibrational absorption lines of silane. The latter feature various absorption strengths, thereby enabling depletion measurements over a wide range of process conditions. © 2009 American Institute of Physics.
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ABSTRACT: Silane and hydrogen discharges are widely used for the deposition of silicon thin film solar cells in large area plasmaenhanced chemical vapor deposition reactors. In the case of microcrystalline silicon thin film solar cells, it is of crucial importance to increase the deposition rate in order to reduce the manufacturing costs. This can be performed by using high silane concentration, and usually high RF power and high pressure, all favorable to powder formation in the discharge that generally reduces the deposition rate as well as the deposited material quality. This work presents a study of powder formation using time-resolved optical emission spectroscopy. It is shown that this technique is suitable to detect different regimes in powder formation ranging from powder free discharge to discharge producing large dust particles. Intermediate powder formation regimes include the formation of small silicon clusters at plasma ignition as well as cycle of powder growth and ejection out of the discharge, and both are observable by this low-cost and experimentally simple technique.
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ABSTRACT: We present a laser scribing system for mid-size photovoltaic modules (up to 410 × 520 mm2) implementing a movable diode-pumped solid state laser. In this configuration, the heavy large-area photovoltaic module does not need to be displaced, allowing for faster and overall more compact industrial systems. Furthermore, in the vicinity of the thin-film, critical beam parameters such as the depth of focus are kept constant throughout the scribing process.
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ABSTRACT: We review laser applications in thin-film photovoltaics (thin-film Si, CdTe, and Cu(In,Ga)Se2 solar cells). Lasers are applied in this growing field to manufacture modules, to monitor Si deposition processes, and to characterize opto-electrical properties of thin films. Unlike traditional panels based on crystalline silicon wafers, the individual cells of a thin-film photovoltaic module can be serially interconnected by laser scribing during fabrication. Laser scribing applications are described in detail, while other laserbased fabrication processes, such as laser-induced crystallization and pulsed laser deposition, are briefly reviewed. Lasers are also integrated into various diagnostic tools to analyze the composition of chemical vapors during deposition of Si thin films. Silane (SiH4), silane radicals (SiH3, SiH2, SiH, Si), and Si nanoparticles have all been monitored inside chemical vapor deposition systems. Finally, we review various thin-film characterization methods, in which lasers are implemented.
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A Feltrin, R Bartlome,
C. Battaglia,
M. Boccard,
G Bugnon,
P Bühlmann,
O. Cubero,
M. Despeisse,
X. Niquille,
G Parascandolo,
T Söderström,
B. Strahm,
V. Terrazzoni,
N. Wyrsch,
C. Ballif
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ABSTRACT: Several aspects of the science and technology of thin film silicon for photovoltaic applications will be presented. The potential advantages of this technology over crystalline wafer technology will be discussed. A basic understanding of the material properties of thin film silicon layers enables to assess their potential and limitations when used in photovoltaic devices. A brief review of the production technology for thin films will be given with particular emphasis on amorphous and microcrystalline silicon. As for other photovoltaic technologies, the push for higher efficiency of thin film silicon devices is strong. An appealing feature of these materials is that they can be easily integrated in multi-junction tandem devices. For instance, stacking amorphous and microcrystalline silicon thin films in one tandem cell, the micromorph cell, increases the efficiency well above the characteristic values of single junction cells. The Institute of Microengineering (IMT) has been a pioneer in the research and development of thin film silicon photovoltaics over the last 20 years and several latest developments on are reviewed.
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ABSTRACT: The role of secondary gas-phase reactions during plasma-enhanced chemical vapor deposition of microcrystalline silicon is a controversial subject. In this paper, we show that the enhancement of such reactions is associated with the improvement of material properties of absorber layers deposited at high constant rate. We detect powder, a product of secondary gas-phase reactions, via infrared laser absorption spectroscopy, laser light scattering, and optical emission spectroscopy. As the powder formation is increased, we measure a systematic improvement of device performance. This demonstrates that secondary gas-phase reactions are not detrimental to the material quality of microcrystalline silicon deposited at high rate. © 2010 American Institute of Physics.
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ABSTRACT: In silicon heterojunction solar cells, thin amorphous silicon layers passivate the crystalline silicon wafer surfaces. By using in situ diagnostics during plasma-enhanced chemical vapor deposition (PECVD), the authors report how the passivation quality of such layers directly relate to the plasma conditions. Good interface passivation is obtained from highly depleted silane plasmas. Based upon this finding, layers deposited in a large-area very high frequency (40.68 MHz) PECVD reactor were optimized for heterojunction solar cells, yielding aperture efficiencies up to 20.3% on 4 cm2
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A Feltrin, R Bartlome,
C. Battaglia,
M. Boccard,
G Bugnon,
P Buehlmann,
O. Cubero,
M. Despeisse,
D. Domine,
F.-J. Haug,
F. Meillaud,
X. Niquille,
G Parascandolo,
T. Soederstroem,
B. Strahm,
V. Terrazzoni,
N. Wyrsch,
C. Ballif
[show abstract]
[hide abstract]
ABSTRACT: Several aspects of the science and technology of thin film silicon for photovoltaic applications will be presented. The potential advantages of this technology over crystalline wafer technology will be discussed. A basic understanding of the material properties of thin film silicon layers enables to assess their potential and limitations when used in photovoltaic devices. A brief review of the production technology for thin films will be given with particular emphasis on amorphous and microcrystalline silicon. As for other photovoltaic technologies, the push for higher efficiency of thin film silicon devices is strong. An appealing feature of these materials is that they can be easily integrated in multi-junction tandem devices. For instance, stacking amorphous and microcrystalline silicon thin films in one tandem cell, the micromorph cell, increases the efficiency well above the characteristic values of single junction cells. The Institute of Microengineering (IMT) has been a pioneer in the research and development of thin film silicon photovoltaics over the last 20 years and several latest developments on are reviewed.
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ABSTRACT: Hydrogenated microcrystalline silicon (μc-Si:H) growth by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) is studied in an industrial-type parallel plate KAI reactor. Combined plasma and material characterization techniques allow to assess critical deposition parameters for the fabrication of high quality material. A relation between low intrinsic stress of the deposited i-layer and better performing solar cell devices is identified. Significant solar cell device improvements were achieved based on these findings: high open circuit voltages above 520 mV and fill factors above 74% were obtained for 1 μm thick μc-Si:H single junction cells and a 1.2 cm2 micromorph device with 12.3% initial (Voc=1.33 V, FF=72.4%, Jsc=12.8 mA cm−2) and above 10.0% stabilized efficiencies.
Solar Energy Materials and Solar Cells.
