Degradation of a Cu/sub x/S/CdS solar cell in hot, moist air and recovery in hydrogen and air

Journal Article · Tue Nov 01 04:00:00 EST 1983 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.331858· OSTI ID:5520067

Partain, L D; McLeod, P S; Duisman, J A; Peterson, T M; Sawyer, D E; Dean, C S

A polycrystalline, thin-film Cu/sub x/S/CdS solar cell was exposed to air saturated with water vapor at temperatures between 27 and 67 /sup 0/C for up to 6 1/2 h. The short-circuit current decreased progressively from 11.7 to 1.02 mA/cm/sup 2/. Subsequent heating in hydrogen at 150 /sup 0/C for 680 h and in 170 /sup 0/C air for 5 h restored the short-circuit current to 14.4 mA/cm/sup 2/. Modeling of the measured quantum yield indicates that the degradation could be quantitatively explained by two effects: (1) the Cu/sub x/S minority carrier electron diffusion length decreasing from 0.23 to 0.02 ..mu..m (+- 20%) and (2) the Cu/sub x/S optical band gap increasing from 1.16 to 1.46 eV (+- 3%). The recovery was quantitatively modeled by the Cu/sub x/S diffusion length increasing back to 0.24 ..mu..m and the Cu/sub x/S band gap returning to 1.16 eV. A Burstein--Moss analysis shows the band-gap shift is due to the Fermi level penetration of the valence band as the measured hole concentration increased from 1.03(10/sup 20/) cm/sup -3/ to 4.62(10/sup 21/) cm/sup -3/ during degradation. A new band structure is proposed with six equivalent, indirect, valence band maxima located at 1.16 eV (+- 3%) below the conduction band edge followed by two direct maxima located at 1.28 and 1.8 eV (+- 3%) below the conduction band edge. A density-of-states effective mass ratio for holes of 2.0 (+- 30%) is found. The sharp decrease and recovery in diffusion length is explained by a transition between phonon-assisted and direct minority carrier recombination with changes in Cu/sub x/S hole concentration.

• Research Organization: Chevron Research Company, Richmond, California 94802
• OSTI ID: 5520067
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 54:11; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140501* -- Solar Energy Conversion-- Photovoltaic Conversion
AIR
CADMIUM COMPOUNDS
CADMIUM SULFIDE SOLAR CELLS
CADMIUM SULFIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER SULFIDES
CRYSTALS
CURRENTS
DIRECT ENERGY CONVERTERS
ELECTRIC CURRENTS
ELEMENTS
EQUIPMENT
FILMS
FLUIDS
GASES
GLASS
HEATING
HYDROGEN
INHIBITION
INORGANIC PHOSPHORS
MEDIUM TEMPERATURE
MOISTURE
NONMETALS
PHOSPHORS
PHOTOELECTRIC CELLS
PHOTOVOLTAIC CELLS
POLYCRYSTALS
RECOVERY
REGENERATION
SATURATION
SOLAR CELLS
SOLAR EQUIPMENT
SORPTIVE PROPERTIES
SULFIDES
SULFUR COMPOUNDS
SURFACE PROPERTIES
THERMAL DEGRADATION
THIN FILMS
TRANSITION ELEMENT COMPOUNDS