Silicon materials task of the low cost solar array project (Phase III). Effect of impurities and processing on silicon solar cells. Fifteenth quarterly report, April-June 1979

Technical Report · Sun Jul 01 04:00:00 EDT 1979

DOI:https://doi.org/10.2172/5720677· OSTI ID:5720677

Hopkins, R H; Davis, J R; Blais, P D; Rohatgi, A; Campbell, R B; Rai-Choudhury, P; Stapleton, R E; Mollenkopf, H C; McCormick, J R

The overall objective of this program is to define the effects of impurities, various thermochemical processes, and any impurity-process interactions on the performance of terrestrial silicon solar cells. The results of the study form a basis for silicon producers, wafer manufacturers, and cell fabricators to develop appropriate cost-benefit relationships for the use of less pure, less costly Solar Grade silicon. The first reported determinations of the segregation coefficients of tungsten, tantalum, and cobalt for the Czochralski pulling of silicon single crystals were performed. Sensitive neutron activation analysis was used to determine the metal impurity content of the silicon (C/sub S/) while atomic absorption was used to measure the metal content of the residual liquid (C/sub L/) from which the doped crystals were grown. Gettering of Ti-doped silicon wafers improves cell performance by 1 to 2% (absolute) for the highest temperatures and longest times. The measured profile for Ti centers formed after an 850/sup 0/C gettering operation was fitted by a mathematical expression for the out-diffusion of an impurity species. By means of cell performance data and the newly-measured segregation coefficients curves were computed to predict the variation in cell efficiency with impurity concentration for Mo, Ta, W, Nb, and Co, materials commonly employed in the construction of high temperature silicon processing equipment. Using data for second and third generation n-base ingots the cell performance curves were updated for single impurities in n-type silicon. Most impurities degrade n-base cells less than p-base devices. The effect is larges for Mo, Al, Mn, Ti, and V while Fe and Cr behave much the same in both types of solar cells. In contrast Ni and Cu both degrade n-base devices (apparently by a junction mechanism) more severely than p-base cells. (WHK)

• Research Organization: Westinghouse Research and Development Center, Pittsburgh, PA (USA)
• DOE Contract Number: NAS-7-100-954331
• OSTI ID: 5720677
• Report Number(s): DOE/JPL/954331-7
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140501* -- Solar Energy Conversion-- Photovoltaic Conversion
ABSORPTION SPECTROSCOPY
ACTIVATION ANALYSIS
ALUMINIUM
CARBON
CHEMICAL ANALYSIS
COBALT
CRYOGENIC FLUIDS
CRYSTAL GROWTH
CRYSTAL GROWTH METHODS
CZOCHRALSKI METHOD
DATA
DATA FORMS
DIRECT ENERGY CONVERTERS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
ETCHING
EXPERIMENTAL DATA
FLUIDS
GETTERING
IMPURITIES
INFORMATION
IRON
ISOLATED VALUES
METALS
MOLYBDENUM
NIOBIUM
NONMETALS
NUMERICAL DATA
OXYGEN
PERFORMANCE
PHOTOELECTRIC CELLS
PHOTOVOLTAIC CELLS
PHYSICAL PROPERTIES
REFRACTORY METALS
SEMIMETALS
SILICON
SILICON SOLAR CELLS
SOLAR CELLS
SPECTROSCOPY
SURFACE FINISHING
TANTALUM
TITANIUM
TRANSITION ELEMENTS
TUNGSTEN
VANADIUM