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Studies of Basic Electronic Properties of CdTe-Based Solar Cells and Their Evolution During Processing and Stress: Final Technical Report, 16 October 2001 - 31 August 2005

Description: This report describes basic issues behind CdTe/CdS cell performance and stability, such as the nature and electronic properties of impurities and defects that control the majority carrier concentration, mechanisms of dopant compensation, recombination processes, their nature and properties, migration and transformation of defects under various processing, stress, and operating conditions. We believe that a better basic understanding of the specific influence of grain boundaries, especially for fine-grain materials such as those making up CdTe-based cells, is now one of the most important issues we must address. We need to clarify the role of grain boundaries in forming the film electronic properties, as well as those of the p-n junction.
Date: February 1, 2007
Creator: Kaydanov, V. I. & Ohno, T. R.
Partner: UNT Libraries Government Documents Department

Process Development and Basic Studies of Electrochemically Deposited CdTe-Based Solar Cells; Annual Technical Report, Phase I: May 15, 1998 - May 14, 1999

Description: The project describes long-term research and development issues related to polycrystalline thin-film solar cells. The general research approach is based on combining activities aimed at improvement of cell performance and stability with activities aimed at increasing fundamental understanding of the properties of materials making up the cells: CdTe, CdS, multi-layer back contact, and transparent conducting oxide (TCO) front contact. The authors emphasize the relation between structural and electronic material properties and various processing procedures, as well as the microscopic mechanisms responsible for the cell performance and its degradation. Major results and conclusions of this project include: (1) Stress tests of the cells under various stress conditions revealed conditions providing the most severe degrading of different cell parameters; (2) Consecutive stress testing under different bias revealed some reversible effects; (3) Preliminary analysis of the data obtained demonstrated a significant role of electromigration of the charged defects/impurities; (4) Some new approaches for the cell characterization and the data analysis were developed and checked experimentally; (5) New stress test experiments were planned for continued studies of degradation mechanisms.
Date: August 25, 2000
Creator: Kaydanov, V.I. & Ohno, T.R.
Partner: UNT Libraries Government Documents Department

Studies of Basic Electronic Properties of CdTe-Based Solar Cells and Their Evolution During Processing and Stress; Annual Technical Report, 1 November 2005 - 31 October 2006

Description: We describe the results of our continuing study of deep electronic states controlling open-circuit voltage in CdTe/CdS thin-film solar cells (Task 1). The study includes: (1) analysis of factors affecting trap signatures derived from admittance spectroscopy and capacitance transients measurements, such as activation-energy capture cross-sections and trap-density estimates, and (2) comparative studies of cells received from four different sources and prepared with significant variations in cell structure and processing procedures.
Date: January 1, 2007
Creator: Beach, J.; Seymour, F. H.; Kaydanov, V. I. & Ohno, T. R.
Partner: UNT Libraries Government Documents Department

Process Development and Basic Studies of Electrochemically Deposited CdTe-Based Solar Cells; Annual Technical Report, Phase II, 16 May 1999-13 May 2000

Description: This project, carried out at the Colorado School of Mines, addresses long-term research and development issues related to polycrystalline thin-film solar cells. Our general research approach is based on combining activities aimed at improving cell performance and stability with activities aimed at increasing our fundamental understanding of the properties of materials making up the cells: CdTe, CdS, multilayer back-contact, and transparent conducting oxide (TCO) from contact. We emphasize the relation between structural and electronic materials properties and various processing procedures, as well as the microscopic mechanisms responsible for the cell performance and its degradation. Section 1 presents studies of degradation under stressing of the cells with differently processed CdTe and different back contents. Section 2 presents studies of deep traps in the electrodeposited (ED) CdTe cells performed in collaboration at NREL. Section 3 reports studies of the spectral dependencies of photocurrent, and their spatial distribution over the cross-section of the ED CdTe cells were performed using near-field scanning optical microscopy (NSOM). Section 4 discusses the impedance spectroscopy of CdTe and CdS thin films. Section 5 presents studies of band spectrum and electron scattering in transparent conducting oxides. Appendices present data on personnel involved in the studies, laboratory improvements, and publications.
Date: April 3, 2001
Creator: Kaydanov, V. I. & Ohno, T. R.
Partner: UNT Libraries Government Documents Department

Polycrystalline Thin-Film Cadmium Telluride Solar Cells Fabricated by Electrodeposition; Final Technical Report, 20 March 1995-15 June 1998

Description: This report summarizes work performed by the Colorado School of Mines Department of Physics under this subcontract. Based on the studies conducted, researchers increased the efficiency of the cells with electrodeposited CdTe and CBD CdS by 3% on average ({approx}30 relative %). The improvement came from 1. Optimization of CdS initial thickness taking into account CdS consumption of CdTe during the CdTe/CdS post-deposition treatment; optimization of CdS post-deposition treatment with CdCl2 aimed at prevention of Te diffusion into CdS and improvement of the CdS film morphology and electronic properties. That led to a considerable increase in short circuit current, by 13% on average. 2. Optimization of CdTe thickness and post-deposition treatment which led to a significant increase in Voc, by {approx}70 mV. The highest Voc obtained exceeded 800 mV. 3. Development of a ZnTe:Cu/Metal back contact processing procedure that included selection of optimal Cu content, deposition regime and post-deposition treatment conditions. As a result, back contact resistance as low as 0.1W-cm2 was obtained. The cell stability was measured on exposure to accelerated stress conditions. Preliminary studies of some new approaches to improvement of CdS/CdTe structure were conducted.
Date: January 27, 1999
Creator: Trefny, J. U.; Mao, D.; Kaydanov, V.; Ohno, T. R.; Williamson, D. L.; Collins, R. et al.
Partner: UNT Libraries Government Documents Department