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Title: 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

Abstract

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.

Authors:
;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
899988
Report Number(s):
NREL/SR-520-41129
ADJ-2-30630-05; TRN: US200709%%518
DOE Contract Number:
AC36-99-GO10337
Resource Type:
Technical Report
Resource Relation:
Related Information: Work performed by Colorado School of Mines, Golden, Colorado
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; DEFECTS; GRAIN BOUNDARIES; IMPURITIES; PERFORMANCE; P-N JUNCTIONS; PROCESSING; RECOMBINATION; SOLAR CELLS; STABILITY; TRANSFORMATIONS; ELECTROLUMINESCENCE; PHOTOLUMINESCENCE; CHARGE INJECTION SPECTROSCOPY; SCANNING TUNNELING MICROSCOPY; ELECTRODEPOSITION; ADMITTANCE SPECTROSCOPY; CAPACITANCE TRANSIENTS; DEEP ELECTRONIC STATES; CHEMICAL-BATH DEPOSITION; POST-DEPOSITION ANNEALING; GAS-TRANSPORT DEPOSITION; GAS-JET SYSTEM; OPTIMIZATION; Solar Energy - Photovoltaics

Citation Formats

Kaydanov, V. I., and Ohno, T. R.. 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. United States: N. p., 2007. Web. doi:10.2172/899988.
Kaydanov, V. I., & Ohno, T. R.. 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. United States. doi:10.2172/899988.
Kaydanov, V. I., and Ohno, T. R.. Thu . "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". United States. doi:10.2172/899988. https://www.osti.gov/servlets/purl/899988.
@article{osti_899988,
title = {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},
author = {Kaydanov, V. I. and Ohno, T. R.},
abstractNote = {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.},
doi = {10.2172/899988},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}

Technical Report:

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  • 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.
  • This report describes the long-term research and development issues related to polycrystalline thin-film solar cells. Our general research approach is based on combining activities aimed at improvement of cell performance and stability with activities aimed at increasing our fundamental understanding of the properties of materials making up the cells: CdTe, CdS, multi-layer back-contact, and transparent conducting oxide (TCO) front-contact. We 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. There is a lack of knowledge and understanding of basic issues behind themore » 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 the dopant compensation, recombination centers, their nature and properties, diffusion, electro migration and transformation of defects under various processing, stress, and operating conditions. We believe that better basic understanding of the specific influence of polycrystallinity, especially for fine-grain materials characteristic of 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. It is important to study and understand the influence of the grain boundaries on the spatial distribution and migration of impurities and electrically active defects. To fulfill these tasks, one needs to develop new methods and techniques (or adjust existing ones) for material characterization, as well as develop more sophisticated approaches to data analysis and modeling.« less
  • This report describes our experimental studies which have been concentrated in roughly five areas. Specifically: (1) We have examined a?Si:H grown very close to the microcrystalline phase boundary, so-called''edge material,'' to help understand why such material is more stable with respect to light-induced degradation; (2) We have also studied the electronic properties, and degradation characteristics of mixed phase material that is mostly a?Si:H, but which contains a significant microcrystalline component; (3) We have examined the electronic properties of high deposition rate material. These studies have included both moderately high deposition rate material (up to 6/s) produced by the PECVD growthmore » method, and extremely high deposition rate material (up to 130/s) produced by the HWCVD growth method. (4) We have examined series of a-Si,Ge:H alloys from several sources. In one extensive series of studies we examined low Ge fraction alloys in an attempt to learn more about the fundamentals of degradation in general. In a couple other studies we evaluated the properties of a-Si,Ge:H alloys produced by methods we had not previously examined. (5) Finally, for three different types of samples we compared basic material properties with companion cell performance data. This was carried out in each case on series of samples for which one or more specific deposition parameters were varied systematically.« less
  • The scope of the work under this subcontract has involved investigating engineered improvements in the performance and stability of solar cells in a systematic way, which included the following four tasks: (1) Materials research and device development; (2) Process improvement directed by real time diagnostics; (3) Device loss mechanisms; and (4) Characterization strategies for advanced materials Our work has resulted in new and important insights into the deposition of a-Si:H-based materials, as well as into the nature of the Staebler-Wronski Effect (SWE). Presumably, many of these insights will be used by industrial partners to develop more systematic approaches in optimizingmore » solar cells for higher performance and stability. This effort also cleared up several serious misconceptions about the nature of the p-layer in cells and the SWE in materials and cells. Finally, the subcontract identified future directions that should be pursued for greater understanding and improvement.« less
  • This project addresses most of the key CdTe technology areas, with focus on improving the manufacturability and long-term stability of this technology. The activities over this 3-year period include developing simplified processing, studying novel front and back contacts, and improving long-term stability. This report describes work carried out during the last year of the project. The solar cells discussed below are fabricated by various deposition technologies that include chemical vapor deposition, chemical-bath deposition, close-spaced sublimation, and rf-sputtering. The devices are routinely evaluated using standard solar cell analytical techniques such as dark and light current-voltage, spectral response, and capacitance-voltage measurements.