Effects of oxygen during close-spaced sublimation of CdTe solar cells
- National Renewable Energy Lab., Golden, CO (United States)
The presence of oxygen during close-spaced sublimation (CSS) deposition of CdTe has been regarded as necessary for high-efficiency CdS/CdTe solar cells. To date, research has focused on the effect of oxygen on the acceptor density in the CdTe absorber. The authors find that although oxygen may influence the doping density, a perhaps more significant effect is its influence on nucleation and growth of the film. Oxygen partial pressures of 0 to 24 torr and total pressures of 5 to 45 torr (balance He) have been explored for CSS depositions. They find that increasing the O{sub 2} partial pressure increases the density of CdTe nucleation sites, thereby suppressing pinhole formation and likely reducing defects at the junction. However, increasing O{sub 2} also tends to decrease grain size and faceting in the films. In addition to influencing the film properties, O{sub 2} adversely affects the source material, producing non-uniformly oxidized surfaces that reduce deposition rates and impair device uniformity and run-to-run reproducibility. The authors have also determined that the graphite susceptors typically used with CSS deposition convert a portion of the oxygen ambient to CO and CO{sub 2} during deposition. The amount converted is highly dependent on the type and age of the graphite susceptor used. The CO{sub x} byproducts are not efficiently incorporated in the CdTe film and do not influence the deposition as oxygen does. They describe the effect of the changing oxygen partial pressure during the course of deposition. Finally, they report high-efficiency solar cells (12.8% AM1.5) made without oxygen.
- Sponsoring Organization:
- National Renewable Energy Lab., Golden, CO (United States)
- DOE Contract Number:
- AC36-83CH10093
- OSTI ID:
- 417695
- Report Number(s):
- CONF-960401--; ISBN 1-55899-329-0
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
ANNEALING
BOROSILICATE GLASS
CADMIUM SULFIDES
CADMIUM TELLURIDE SOLAR CELLS
CADMIUM TELLURIDES
CATHODOLUMINESCENCE
CHEMICAL COATING
CURRENT DENSITY
EFFICIENCY
ELECTRIC POTENTIAL
FILL FACTORS
GRAIN SIZE
ION MICROPROBE ANALYSIS
MASS SPECTROSCOPY
MICROSTRUCTURE
MORPHOLOGY
NUCLEATION
OXIDATION
OXYGEN
PARTIAL PRESSURE
PERFORMANCE
PHYSICAL VAPOR DEPOSITION
SCANNING ELECTRON MICROSCOPY
SURFACE CLEANING
TIN OXIDES
X-RAY DIFFRACTION