Electrical properties of WSe/sub 2/, WS/sub 2/, MoSe/sub 2/, MoS/sub 2/, and their use as photoanodes in a semiconductor/liquid junction solar cell
The electrical resistivity and Hall effect perpendicular to the c-axis of single crystals of n-type WSe/sub 2/, MoSe/sub 2/, WS/sub 2/, and MoS/sub 2/ were studied in the extrinsic conduction temperature range (77/sup 0/K to 300/sup 0/K). It was found that a single-donor energy level can be assigned to the crystals of WSe/sub 2/ and MoSe/sub 2/, even for crystals from different growth ampoules. E/sub D/ = (108 +- 4) MeV for WSe/sub 2/ and (64 +- 2) MeV for MoSe/sub 2/. The electron Hall mobility of these two compounds depends strongly on temperature. ..mu../sub H/ approx. T/sup -2/ /sup 4/ for WSe/sub 2/ and approx. T/sup -2/ /sup 6/ for MoSe/sub 2/. For WS/sub 2/ and MoS/sub 2/, the results were not as consistent as those for WSe/sub 2/ and MoSe/sub 2/ because of poorer crystal quality. The resistivity parallel to the c-axis was also studied on single crystals of WSe/sub 2/ and MoSe/sub 2/. The resistivity anisotropy of these two compounds is small, compared to that reported on natural single crystals of MoS/sub 2/. Single crystals of n-type WSe/sub 2/, MoSe/sub 2/, WS/sub 2/, and MoS/sub 2/ were employed as photoanodes in a photoelectrochemical solar cell with a variety of redox couples as the charge-transfer agents. It was found that WSe/sub 2/ is the best photoelectrode material of all, and the redox couple, I/sup -//I/sub 3//sup -/, provides a fast-kinetics path for electron transfer. An efficiency as high as 10.2% was achieved for an n-WSe/sub 2//I/sup -/-I/sub 3//sup -//Pt cell, and 9,4% when MoSe/sub 2/ was used. The cell (n-WSe/sub 2//I/sup -/-I/sub 3//sup -//C) is stable for at least one year. Polycrystalline samples of n-WSe/sup 2/ were also studied as photoanodes in such a cell, but their performance is poor, compared with that of single crystals, because defects, such as steps on the crystal surface and grain boundaries, act as recombination centers. Transmission spectra of single crystals of WSe/sub 2/ were studied near the fundamental absorption edge. Based on the experimental results, it was concluded that WSe/sub 2/ is an indirect band-gap material.
- Research Organization:
- Ames Lab., IA (USA)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 6668128
- Report Number(s):
- IS-T-1045; ON: DE83004789
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
MOLYBDENUM SELENIDES
ELECTRICAL PROPERTIES
MOLYBDENUM SULFIDES
PHOTOELECTROCHEMICAL CELLS
PHOTOANODES
TUNGSTEN SELENIDES
TUNGSTEN SULFIDES
CARRIER DENSITY
CARRIER MOBILITY
CRYSTAL STRUCTURE
EFFICIENCY
ELECTRIC CONDUCTIVITY
ELECTROLYTES
ENERGY LEVELS
ENERGY-LEVEL DENSITY
EXPERIMENTAL DATA
GRAIN BOUNDARIES
HALL EFFECT
LIGHT TRANSMISSION
PHOTOCURRENTS
POLYCRYSTALS
RECOMBINATION
SPECTRA
TEMPERATURE DEPENDENCE
ANODES
CHALCOGENIDES
CRYSTALS
CURRENTS
DATA
ELECTRIC CURRENTS
ELECTROCHEMICAL CELLS
ELECTRODES
EQUIPMENT
INFORMATION
MICROSTRUCTURE
MOBILITY
MOLYBDENUM COMPOUNDS
NUMERICAL DATA
PHYSICAL PROPERTIES
SELENIDES
SELENIUM COMPOUNDS
SOLAR EQUIPMENT
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TUNGSTEN COMPOUNDS
140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)
360603 - Materials- Properties