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Author: Xiaoyue Zhang Publisher: ISBN: Category : Languages : en Pages : 310
Book Description
This dissertation discusses the formation of cadmium telluride (CdTe) using potential pulse atomic layer deposition (PP-ALD) and metal thin films (copper and gold) using surface limited redox replacement (SLRR). Both materials play important roles in photovoltaic devices. PP-ALD is an electrodeposition methodology similar to co-deposition because it uses one solution containing all precursors. However, instead of maintaining one deposition potential as with codeposition, potentials are varied quickly between a cathodic and an anodic potential throughout deposition. Each short pulse aims to limit the amount deposited during cathodic potential and strip the excess in the following anodic potential so that thermodynamically stable compound remains without elemental excess buried beneath the later-grown film. To achieve high quality CdTe thin film, changes in deposition potential and solution flow effects were first monitored and optimized. Parametric variables for controlling the Cd/Te ratio and morphology are also established. X-ray diffraction (XRD), Scanning electron microscope (SEM), Electron probe microanalysis (EPMA), Energy dispersive X-Ray Analyzer (EDX) were used to characterize the resulting CdTe films. Results indicated that deposited CdTe was stoichiometric, high crystalline with a smooth, continuous morphology using an optimized PP-ALD method. The optimized PP-ALD method was also applied on nanostructured Au electrodes. Initial results showed high quality deposits with reproducible stoichiometry, which could open pathways for semiconductor and nanostructure incorporation. Cu and Au thin films were formed on metal and semiconductor substrates via surface limited redox replacement (SLRR). An atomic layer of cadmium was first deposited as a sacrificial layer, and then replaced with ions of more noble metals such as Cu2+ or Au3+ to form Cu or Au atomic layer. Uniform and reasonably flat metal thin films with controllable thickness were produced by multiple repetitions of SLRR cycles with great linear growth with respect to cycle numbers. The resulting metal thin films were characterized using coulometry, SEM, EDX and EPMA. They confirmed deposited metal thin films had a conformal, flat morphology with no roughness development, nor Cd incorporation in the deposition process.
Author: Xiaoyue Zhang Publisher: ISBN: Category : Languages : en Pages : 310
Book Description
This dissertation discusses the formation of cadmium telluride (CdTe) using potential pulse atomic layer deposition (PP-ALD) and metal thin films (copper and gold) using surface limited redox replacement (SLRR). Both materials play important roles in photovoltaic devices. PP-ALD is an electrodeposition methodology similar to co-deposition because it uses one solution containing all precursors. However, instead of maintaining one deposition potential as with codeposition, potentials are varied quickly between a cathodic and an anodic potential throughout deposition. Each short pulse aims to limit the amount deposited during cathodic potential and strip the excess in the following anodic potential so that thermodynamically stable compound remains without elemental excess buried beneath the later-grown film. To achieve high quality CdTe thin film, changes in deposition potential and solution flow effects were first monitored and optimized. Parametric variables for controlling the Cd/Te ratio and morphology are also established. X-ray diffraction (XRD), Scanning electron microscope (SEM), Electron probe microanalysis (EPMA), Energy dispersive X-Ray Analyzer (EDX) were used to characterize the resulting CdTe films. Results indicated that deposited CdTe was stoichiometric, high crystalline with a smooth, continuous morphology using an optimized PP-ALD method. The optimized PP-ALD method was also applied on nanostructured Au electrodes. Initial results showed high quality deposits with reproducible stoichiometry, which could open pathways for semiconductor and nanostructure incorporation. Cu and Au thin films were formed on metal and semiconductor substrates via surface limited redox replacement (SLRR). An atomic layer of cadmium was first deposited as a sacrificial layer, and then replaced with ions of more noble metals such as Cu2+ or Au3+ to form Cu or Au atomic layer. Uniform and reasonably flat metal thin films with controllable thickness were produced by multiple repetitions of SLRR cycles with great linear growth with respect to cycle numbers. The resulting metal thin films were characterized using coulometry, SEM, EDX and EPMA. They confirmed deposited metal thin films had a conformal, flat morphology with no roughness development, nor Cd incorporation in the deposition process.
Author: Publisher: ISBN: Category : Languages : en Pages : 35
Book Description
During the past year, Colorado School of Mines (CSM) researchers performed systematic studies of the growth and properties of electrodeposition CdS and back-contact formation using Cu-doped ZnTe, with an emphasis on low Cu concentrations. CSM also started to explore the stability of its ZnTe-Cu contacted CdTe solar cells. Researchers investigated the electrodeposition of CdS and its application in fabricating CdTe/CdS solar cells. The experimental conditions they explored in this study were pH from 2.0 to 3.0; temperatures of 80 and 90 C; CdCl2 concentration of 0.2 M; deposition potential from -550 to -600 mV vs. Ag/AgCl electrode; [Na2S2O4] concentration between 0.005 and 0.05 M. The deposition rate increases with increase of the thiosulfate concentration and decrease of solution pH. Researchers also extended their previous research of ZnTe:Cu films by investigating films doped with low Cu concentrations (
Author: Sheng Shen Publisher: ISBN: Category : Languages : en Pages : 298
Book Description
This dissertation discussed the layer-by-layer growth of CdS thin film using electrochemical atomic layer deposition (E-ALD) as well as the investigations into the possible fabrication of both substrate and superstrate configurations of CdTe/CdS solar cells. E-ALD is the electrochemical equivalence of gas phase atomic layer deposition (ALD). Similar to ALD, E-ALD allows for the layer-by-layer deposition of materials using surface-limited reaction. Underpotential deposition (UPD) is usually used in E-ALD, allowing for atomically thick layers of materials to be deposited on a second material at a potential before the potential needed for the element to deposit on itself. In this report, CdS thin films with different thicknesses were grown using E-ALD. Results indicated that the E-ALD grown CdS on Au was stoichiometric, crystalline, uniform, and is N-type. Formation of CdS on Ag substrates and on ITO was also studied. Preliminary studies on the fabrication of CdS/CdTe photovoltaic device with both superstrate and substrate configuration were also performed. In the substrate configuration, CdTe was first deposited onto Au substrates using 15 minutes of codeposition at -700 mV, followed by electrochemical atomic layer deposition (E-ALD) of CdS on CdTe/Au. In the superstrate configuration, the ITO substrate was first patterned with 1x1 mm2 squares using photolithography, and then treated with electrochemical methods to form Cu nucleation sites on the ITO surface. CdS E-ALD was performed on the treated ITO substrate. CdTe thin films were deposited onto CdS/ITO using pulse plating atomic layer deposition (PP-ALD). A layer of Au was deposited electrochemically on CdTe/CdS/ITO as the back contact. Photoelectrochemical measurements on the substrate configuration showed good P-type response and clean dark current. XRD showed CdTe zinc blend 111 and CdS zinc blend 111 structure. SEM images of the CdTe/CdS/ITO showed compact deposits covering the whole surface. Work on collecting more information on cell performance is on the way.
Author: Publisher: ISBN: Category : Languages : en Pages : 46
Book Description
The objective of this project is to develop improved processes for fabricating CdTe/CdS polycrystalline thin-film solar cells. Researchers used electrodeposition to form CdTe; electrodeposition is a non-vacuum, low-cost technique that is attractive for economic, large-scale production. During the past year, research and development efforts focused on several steps that are most critical to the fabricating high-efficiency CdTe solar cells. These include the optimization of the CdTe electrodeposition process, the effect of pretreatment of CdS substrates, the post-deposition annealing of CdTe, and back-contact formation using Cu-doped ZnTe. Systematic investigations of these processing steps have led to a better understanding and improved performance of the CdTe-based cells. Researchers studied the structural properties of chemical-bath-deposited CdS thin films and their growth mechanisms by investigating CdS samples prepared at different deposition times; investigated the effect of CdCl2 treatment of CdS films on the photovoltaic performance of CdTe solar cells; studied Cu-doped ZnTe as a promising material for forming stable, low-resistance contacts to the p-type CdTe; and investigated the effect of CdTe and CdS thickness on the photovoltaic performance of the resulting cells. As a result of their systematic investigation and optimization of the processing conditions, researchers improved the efficiency of CdTe/CdS cells using ZnTe back-contact and electrodeposited CdTe. The best CdTe/CdS cell exhibited a V{sub oc} of 0.778 V, a J{sub sc} of 22.4 mA/cm2, a FF of 74%, and an efficiency of 12.9% (verified at NREL). In terms of individual parameters, researchers obtained a V{sub oc} over 0.8 V and a FF of 76% on other cells.
Author: Jaime Andres Perez Taborda Publisher: BoD – Books on Demand ISBN: 1789848709 Category : Technology & Engineering Languages : en Pages : 288
Book Description
The field of coatings and thin-film technologies is rapidly advancing to keep up with new uses for semiconductor, optical, tribological, thermoelectric, solar, security, and smart sensing applications, among others. In this sense, thin-film coatings and structures are increasingly sophisticated with more specific properties, new geometries, large areas, the use of heterogeneous materials and flexible and rigid coating substrates to produce thin-film structures with improved performance and properties in response to new challenges that the industry presents. This book aims to provide the reader with a complete overview of the current state of applications and developments in thin-film technology, discussing applications, health and safety in thin films, and presenting reviews and experimental results of recognized experts in the area of coatings and thin-film technologies.
Author: J. U. Trefny Publisher: ISBN: Category : Cadmium telluride Languages : en Pages : 0
Book Description
The objective of this project is to develop improved processes for fabricating CdTe/CdS polycrystalline thin-film solar cells. Researchers used electrodeposition to form CdTe; electrodeposition is a non-vacuum, low-cost technique that is attractive for economic, large-scale production. During the past year, research and development efforts focused on several steps that are most critical to the fabricating high-efficiency CdTe solar cells. These include the optimization of the CdTe electrodeposition process, the effect of pretreatment of CdS substrates, the post-deposition annealing of CdTe, and back-contact formation using Cu-doped ZnTe. Systematic investigations of these processing steps have led to a better understanding and improved performances of the CdTe-based cells.
Author: Jonathan J. Scragg Publisher: Springer Science & Business Media ISBN: 3642229190 Category : Science Languages : en Pages : 220
Book Description
Jonathan Scragg documents his work on a very promising material suitable for use in solar cells. Copper Zinc Tin Sulfide (CZTS) is a low cost, earth-abundant material suitable for large scale deployment in photovoltaics. Jonathan pioneered and optimized a low cost route to this material involving electroplating of the three metals concerned, followed by rapid thermal processing (RTP) in sulfur vapour. His beautifully detailed RTP studies – combined with techniques such as XRD, EDX and Raman – reveal the complex relationships between composition, processing and photovoltaic performance. This exceptional thesis contributes to the development of clean, sustainable and alternative sources of energy
Author: John U. Trefny Publisher: ISBN: Category : Cadmium telluride Languages : en Pages : 0
Book Description
During the past year, Colorado School of Mines (CSM) researchers performed systematic studies of the growth and properties of electrodeposition CdS and back-contact formation using Cu-doped ZnTe, with an emphasis on low Cu concentrations. CSM also started to explore the stability of its ZnTe-Cu contacted CdTe solar cells. Researchers investigated the electrodeposition of CdS and its application in fabricating CdTe/CdS solar cells. The experimental conditions they explored in this study were pH from 2.0 to 3.0; temperatures of 80 and 90 deg. C; CdCl2 concentration of 0.2 M; deposition potential from -550 to -600 mV vs. Ag/AgCl electrode; [Na2S2O4] concentration between 0.005 and 0.05 M. The deposition rate increases with increase of the thiosulfate concentration and decrease of solution pH. Researchers also extended their previous research of ZnTe:Cu films by investigating films doped with low Cu concentrations (
Author: Misle M. Tessema Publisher: ISBN: Category : Solar cells Languages : en Pages : 220
Book Description
A cadmium sulfide / cadmium telluride (CdS/CdTe) solar cell consists of the device stack: Glass substrate / SnO2:F (TCO, transparent conductive oxide) / CdS (n-type semiconductor) / CdTe (p-type semiconductor) / Cu/Au (metal/back contact). During the fabrication process of the CdS and CdTe thin films pinholes are usually formed within these layers (random defects, which are entropy driven). After the semiconductor deposition, and subsequent heat treatments, the solar cell is completed with the deposition of a metal electrode onto the CdTe surface. The presence of a pinhole through the semiconductor layers leads to the formation of a wire like connection through the photovoltaic device (shunt, metal connection of the TCO and metal electrodes), which adversely affects the overall performance of the solar cell. Our proposed solution is to fill these pinholes with a resistive material such as polyaniline, using an electrochemical deposition (electrochemical polymerization) technique. The electrochemical deposition technique is performed by applying a voltage across a conductive substrate (TCO coated glass) and an inert electrode (Pt), both placed inside an electrolyte rich solution containing aniline. The aniline monomer then reacts at the positively charged conductive substrate to form a polymer (polyaniline). After the polyaniline film deposition, this new layer acts as an insulating layer, preventing the back contact (Cu/Au) from electrically contacting the TCO layer, thus avoiding shunting of the solar cell. Characterization techniques employed in this study are: depth profilemeter, x-ray photoelectron spectroscopy, electron spray ionization - mass spectrometry, scanning electron microscopy, energy dispersive spectroscopy and grazing angle incidence x-ray diffraction. Subsequently, this technique is applied to CdTe solar cells that have pinholes and on an artificially scribed pinhole. After the electro deposition of polyaniline the CdTe solar cell is completed by metalizing using a Cu-Au back contact, and characterized by JV-measurements, under AM1.5 (terrestrial spectrum). Thus, we were able to obtain promising results that indicate both the deposition of the polymer on the device and hindrance of shunting of the CdTe solar cell.
Author: Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
A method for forming thin films or layers of cadmium telluride (CdTe) for use in photovoltaic modules or solar cells. The method includes varying the substrate temperature during the growth of the CdTe layer by preheating a substrate (e.g., a substrate with a cadmium sulfide (CdS) heterojunction or layer) suspended over a CdTe source to remove moisture to a relatively low preheat temperature. Then, the method includes directly heating only the CdTe source, which in turn indirectly heats the substrate upon which the CdTe is deposited. The method improves the resulting CdTe solar cell reliability. The resulting microstructure exhibits a distinct grain size distribution such that the initial region is composed of smaller grains than the bulk region portion of the deposited CdTe. Resulting devices exhibit a behavior suggesting a more n-like CdTe material near the CdS heterojunction than devices grown with substrate temperatures held constant during CdTe deposition.
Author: Xiaoyue Zhang
Author: Xiaoyue Zhang
Author: 
Author: Sheng Shen
Author: 
Author: Jaime Andres Perez Taborda
Author: J. U. Trefny
Author: Jonathan J. Scragg
Author: John U. Trefny
Author: Misle M. Tessema
Author: