Process research on polycrystalline silicon material. Final technical report
The performance-limiting mechanism in large-grain polycrystalline silicon solar cells were investigated by fabricating a matrix of 4 cm/sup 2/ solar cells of various thicknesses from 10 cm x 10 cm polycrystalline silicon wafers of several bulk resistivities. The analysis of the illuminated I-V characteristics of the cells of this thickness-resistivity matrix strongly suggest that bulk recombination is the dominant factor limiting the short-circuit current in large-grain polycrystalline silicon, the same mechanism that limits the short-circuit current in single-crystal silicon. Further investigation of the performance-limiting mechanisms consisted of fabricating a set of mini-cell wafers from a selection of 10 cm x 10 cm polycrystalline silicon wafers. A mini-cell wafer contains an array of small (approximately 0.2 cm/sup 2/ in area) photodiodes that are isolated from one another by a mesa structure. The average short-circuit current on different wafers was 3 to 14% lower than that of single-crystal Czochralski silicon. The average open-circuit voltage was 20 to 60 mV less than that of single-crystal silicon. The fill-factor of both polycrystalline and single-crystal silicon cells was equivalent. Lower average values of open-circuit voltage and a greater degree of open-circuit voltage and fill-factor scatter were correlated with the presence of inclusions, which was also correlated with significantly greater values of shunt conductance. Measurement of the dark I-V characteristics of mini-cells from several wafers with few inclusions indicates that spatial variations in quasi-neutral recombination current are the dominant cause of open-circuit voltage variations. A damage-gettering heat-treatment was investigated and was found to improve the minority-carrier diffusion length in low lifetime polycrystalline silicon. However, extended high temperature heat-treatment did not further improve, but rather degraded, the lifetime.
- Research Organization:
- Solarex Corp., Rockville, MD (USA)
- DOE Contract Number:
- NAS-7-100-955902
- OSTI ID:
- 7147170
- Report Number(s):
- DOE/JPL/955902-83/11; ON: DE84011716
- Resource Relation:
- Other Information: Portions are illegible in microfiche products. Original copy available until stock is exhausted
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
SILICON
ELECTRICAL PROPERTIES
SILICON SOLAR CELLS
PERFORMANCE
ELECTRIC CONDUCTIVITY
ELECTRIC CURRENTS
ELECTRIC POTENTIAL
FABRICATION
FILL FACTORS
GETTERING
POLYCRYSTALS
RECOMBINATION
CRYSTALS
CURRENTS
DIRECT ENERGY CONVERTERS
ELEMENTS
EQUIPMENT
PHOTOELECTRIC CELLS
PHOTOVOLTAIC CELLS
PHYSICAL PROPERTIES
SEMIMETALS
SOLAR CELLS
SOLAR EQUIPMENT
140501* - Solar Energy Conversion- Photovoltaic Conversion
360603 - Materials- Properties