High Efficiency Cadmium and Zinc Telluride-based Thin Film Solar Cells PDF Download
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Languages : en
Pages : 83
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Polycrystalline Cd{sub 1-x}Zn(subscript x)Te and Cd{sub 1-x}Mn(subscript x)Te films with a band gap of 1.7 eV were successfully grown on glass/SnO2/CdS substrates by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), respectively. Polycrystalline Cd{sub 1-x}Zn(subscript x)Te films grown by MBE resulted in uniform composition and sharp interfaces. However, polycrystalline Cd{sub 1-x}Mn(subscript x)Te films grown by MOCVD showed nonuniform compositions and evidence of manganese accumulation at the Cd{sub 1-x}Mn(subscript x)Te/CdS interface. We found that manganese interdiffuses and replaces cadmium in the CdS film. By improving the CdTe/CdS interface and, thus, reducing the collection function effects, the efficiency of the MOCVD CdTe cell can be improved to about 13.5%. MBE-grown CdTe cells also produced 8%--9% efficiencies. The standard CdTe process was not optimum for ternary films and resulted in a decrease in the band gap. Recent results indicate that CdCl2 + ZnCl2 chemical treatment may prevent the band-gap reduction, and that chromate etch (rather than bromine etch) may provide the solution to contact resistance in the ternary cells.
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Category :
Languages : en
Pages : 83
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Book Description
Polycrystalline Cd{sub 1-x}Zn(subscript x)Te and Cd{sub 1-x}Mn(subscript x)Te films with a band gap of 1.7 eV were successfully grown on glass/SnO2/CdS substrates by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), respectively. Polycrystalline Cd{sub 1-x}Zn(subscript x)Te films grown by MBE resulted in uniform composition and sharp interfaces. However, polycrystalline Cd{sub 1-x}Mn(subscript x)Te films grown by MOCVD showed nonuniform compositions and evidence of manganese accumulation at the Cd{sub 1-x}Mn(subscript x)Te/CdS interface. We found that manganese interdiffuses and replaces cadmium in the CdS film. By improving the CdTe/CdS interface and, thus, reducing the collection function effects, the efficiency of the MOCVD CdTe cell can be improved to about 13.5%. MBE-grown CdTe cells also produced 8%--9% efficiencies. The standard CdTe process was not optimum for ternary films and resulted in a decrease in the band gap. Recent results indicate that CdCl2 + ZnCl2 chemical treatment may prevent the band-gap reduction, and that chromate etch (rather than bromine etch) may provide the solution to contact resistance in the ternary cells.
Author: A. Rohatgi
Publisher:
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Category : Solar cells
Languages : en
Pages :
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Category :
Languages : en
Pages : 108
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This report describes work to improve the basic understanding of CdTe and ZnTe alloys by growing and characterizing these films along with cell fabrication. The major objective was to develop wide-band-gap (1.6--1.8 eV) material for the top cell, along with compatible window material and transparent ohmic contacts, so that a cascade cell design can be optimized. Front-wall solar cells were fabricated with a glass/SnO2/CdS window, where the CdS film is thin to maximize transmission and current. Wide-band-gap absorber films (E{sub g} = 1.75 eV) were grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD) techniques, which provided excellent control for tailoring the film composition and properties. CdZnTe films were grown by both MBE and MOCVD. All the as-grown films were characterized by several techniques (surface photovoltage spectroscopy, Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS)) for composition, bulk uniformity, thickness, and film and interface quality. Front-wall-type solar cells were fabricated in collaboration with Ametek Materials Research Laboratory using CdTe and CdZnTe polycrystalline absorber films. The effects of processing on ternary film were studied by AES and XPS coupled with capacitance voltage and current voltage measurements as a function of temperature. Bias-dependent spectral response and electrical measurements were used to test some models in order to identify and quantify dominant loss mechanisms.
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Category : Cadmium telluride
Languages : en
Pages : 0
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Author: A. Rohatgi
Publisher:
ISBN:
Category : Cadmium telluride
Languages : en
Pages : 0
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Category :
Languages : en
Pages : 0
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Author:
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Category :
Languages : en
Pages : 97
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This report describes research to demonstrate (1) thin film cadmium telluride solar cells with a quantum efficiency of 75% or higher at 0. 44?m and a photovoltaic efficiency of 11.5% or greater, and (2) thin film zinc telluride and mercury zinc telluride solar cells with a transparency to sub-band-gap radiation of 65% and a photovoltaic conversion efficiency of 5% and 8%, respectively. Work was directed at (1) depositing transparent conducting semiconductor films by solution growth and metal-organic chemical vapor deposition (MOCVD) technique, (2) depositing CdTe films by close-spaced sublimation (CSS) and MOCVD techniques, (3) preparing and evaluating thin film CdTe solar cells, and (4) preparing and characterizing thin film ZnTe, CD{sub 1-x}Zn{sub 1-x}Te, and Hg{sub 1-x}ZnxTe solar cells. The deposition of CdS films from aqueous solutions was investigated in detail, and their crystallographic, optical, and electrical properties were characterized. CdTe films were deposited from DMCd and DIPTe at 400°C using TEGa and AsH3 as dopants. CdTe films deposited by CSS had significantly better microstructures than those deposited by MOCVD. Deep energy states in CdTe films deposited by CSS and MOCVD were investigated. Thin films of ZnTe, Cd{sub 1- x}ZnxTe, and Hg{sub 1-x}ZnxTe were deposited by MOCVD, and their crystallographic, optical, and electrical properties were characterized. 67 refs.
Author: A. Rohatgi
Publisher:
ISBN:
Category : Cadmium telluride
Languages : en
Pages : 100
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Author: Fadhil Khalaf Dahash Alfadhili
Publisher:
ISBN:
Category : Photovoltaic cells
Languages : en
Pages : 100
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Thin film solar cells based on polycrystalline p-type cadmium telluride (CdTe) represent one of these the most promising photovoltaic (PV) device due to high efficiency and low-cost production. Currently, CdTe solar cells provide the lowest cost electricity generation in utility-scale applications, which is a cost-competitive with the traditional power source, fossil fuel. CdTe thin film PV has attained 22.1 % of power conversion efficiency for small area scale and 18.6 % for modules scale. However, the high efficiency of CdTe devices has been achieved by increasing the photo-generated current by changing the traditional window layer (CdS) of CdTe to a wider bandgap material with better band alignment. The open-circuit voltage (VOC) remains below the theoretical limit due to a barrier at the back of the device due to the deep valence band edge of CdTe (-5.9 eV). Voc can be increased by adding a buffer layer between CdTe and the back electrode to decrease band banding and reducing carrier recombination at the back interface. In this thesis, several materials were investigated as a back-buffer layer, such as single-wall carbon nanotube (SWCNT), zinc telluride (ZnTe), tellurium (Te), and cadmium zinc telluride (CZT) to minimize the bend bending at CdTe/back-buffer layer interface. An alternative method to reduce the carrier recombination at the rear surface, the use of aluminum oxide (Al2O3) layer as a passivation layer was also demonstrated. Finally, an effective method of CdCl2 treatment for CZT thin film was investigated. This method shows that zinc (Zn) can be maintained during the heat treatment.
Author: Nowshad Amin
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659369438
Category :
Languages : en
Pages : 148
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Book Description
Thin film cadmium telluride absorbers with cadmium sulphide hetero-junction partner are promising candidates for high efficiency low cost solutions of solar energy harvesting devices. These devices have band gaps well-suited for effective absorption of sunlight. Most importantly, the materials used in these devices can be deposited in a variety of industry-friendly ways, so that the cost associated with manufacturing is generally lower than other available technologies. Although poly-crystalline CdS has been found to be the best suited heterojunction partner for CdTe solar cell, the conventional polycrystalline CdS/CdTe cell has few issues that limit device performance. In order to overcome these problems, this study proposes the introduction of poly-CdS to amorphous oxygenated CdS (a-CdS: O) as window layer. The a-CdS: O window material has higher optical band gap (2.5-3.1 eV), better lattice match with CdTe absorber materials and reduced inter-diffusion tendency of CdS and CdTe layers. This book systematically demonstrates the conversion process of poly CdS to a-CdS: O and develops a strategy for the fabrication of suitable a-CdS: O layer to be applied in CdTe solar ce
