A polycrystalline, thin-film CuxS/CdS solar cell was exposed to air saturated with water vapor at temperatures between 27 and 67 °C for up to 6 1/2 h. The short-circuit current decreased progressively from 11.7 to 1.02 mA/cm2. Subsequent heating in hydrogen at 150 °C for 680 h and in 170 °C air for 5 h restored the short-circuit current to 14.4 mA/cm2. Modeling of the measured quantum yield indicates that the degradation could be quantitatively explained by two effects: (1) the CuxS minority carrier electron diffusion length decreasing from 0.23 to 0.02 μm (±20%) and (2) the CuxS optical band gap increasing from 1.16 to 1.46 eV (±3%). The recovery was quantitatively modeled by the CuxS diffusion length increasing back to 0.24 μm and the CuxS 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(1020) cm−3 to 4.62(1021) cm−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 CuxS hole concentration.
Very intense room-temperature photoluminescence has been observed near 1000 nm in CdS films prepared by spray pyrolysis. Since this material can be easily fabricated into p-n devices, this suggests the possibility of inexpensive electro-optical devices. Also, the photoluminescence spectra of CdS and amorphous Si:H are very similar.
The vapor pressure of pure nitric acid was calculated from the latest thermodynamic data and found in disagreement with the most reliable measurements reported in the literature. This discrepancy is attributed to an error in the standard enthalpy of vaporization, AHmis, used as reference in the calculations. Other possible sources of error are also discussed. New vapor pressure measurements reported by Holeci were subjected to a third-law consistency test and found satisfactory. A new value of 298.15 obtained from these data was used to recalculate the vapor pressure between 263°and 373°K. These computations yielded a normal boiling point of 357.05°K. (83.90°C.) for pure nitric acid.
= 24, Na/AI = < .01) and H-ZSM-5 (Si/AI = 26.5: Na/AI = < .01) with 1.38 grams and 1.35 grams of sample respectively show again that the acidity of these tested samples begin to decline, thus confirming the small sample NH,+-ZSM-5 data presented here. The activity values (k,) of 77.6 and 59.5 for NH4+-ZSM-5 and H-ZSM-5 respectively are plotted in Figure 5.
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