Silicon materials task of the low-cost solar-array project. Effect of impurities and processing on silicon solar cells. Final report

Technical Report · Mon Feb 01 04:00:00 EST 1982

DOI:https://doi.org/10.2172/5358007· OSTI ID:5358007

Hopkins, R. H.; Davis, J. R.; Rohatgi, A.; Hanes, M. H.; Rai-Choudhury, P.; Mollenkopf, H. C.

The object of the program has been to investigate the effects of various processes, metal contaminants, and contaminant-process interactions on the properties of silicon and on the performance of terrestrial silicon solar cells. The study has encompassed topics such as thermochemical (gettering) treatments, base-doping concentration, base-doping type (n vs. p), grain boundary-impurity interaction in polycrystalline devices, and long-term effects of impurities and impurity impacts on high-efficiency cells, as well as a preliminary evaluation of some potential low-cost silicon materials. The effects have been studied of various metallic impurities, introduced singly or in combination into Czochralski, float zone, and polycrystalline silicon ingots and into silicon ribbons grown by the dendritic web process. The solar cell data indicate that impurity-induced performance loss is caused primarily by a reduction in base diffusion length. An analytical model based on this observation has been developed and verified experimentally for both n- and p-base material. Studies of polycrystalline ingots containing impurities indicate that solar cell behavior is species sensitive and that a fraction of the impurities are segregated to the grain boundaries. HCl and POCl gettering improve the performance of single-crystal solar cells containing Fe, Cr, and Ti. In contrast Mo-doped material is barely affected. The efficiencies of solar cells fabricated on impurity-doped wafers is lower when the front junction is formed by ion implantation than when conventional diffusion techniques are used. For most impurity-doped solar cells stability is expected for projected times beyond 20 years. Feedstock impurity concentrations below one part per million for elements like V, or 100 parts per million for more benign impurities like Cu or Ni, will be required.

• Research Organization: Westinghouse Research and Development Center, Pittsburgh, PA (USA)
• DOE Contract Number: NAS-7-100-954331
• OSTI ID: 5358007
• Report Number(s): DOE/JPL/954331-82/1; ON: DE82009390
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140501* -- Solar Energy Conversion-- Photovoltaic Conversion
CHROMIUM
CRYSTAL DOPING
CRYSTAL GROWTH METHODS
CRYSTAL STRUCTURE
CRYSTALS
CZOCHRALSKI METHOD
DATA
DENDRITIC WEB GROWTH METHOD
DIFFUSION
DIFFUSION LENGTH
DIMENSIONS
DIRECT ENERGY CONVERTERS
EFFICIENCY
ELEMENTS
EQUIPMENT
EXPERIMENTAL DATA
GETTERING
GRAIN BOUNDARIES
IMPURITIES
INFORMATION
ION IMPLANTATION
IRON
LENGTH
MATHEMATICAL MODELS
MELTING
METALS
MICROSTRUCTURE
MOLYBDENUM
NUMERICAL DATA
PERFORMANCE
PHASE TRANSFORMATIONS
PHOTOELECTRIC CELLS
PHOTOVOLTAIC CELLS
POLYCRYSTALS
QUANTITY RATIO
QUANTUM EFFICIENCY
SEGREGATION
SENSITIVITY
SERVICE LIFE
SILICON SOLAR CELLS
SOLAR CELLS
SOLAR EQUIPMENT
SPECTRAL RESPONSE
TITANIUM
TRANSITION ELEMENTS
ZONE MELTING