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Title: Cadmium sulfide/copper sulfide heterojunction cell research by sputter deposition. Quarterly technical progress report, March 1, 1981-June 30, 1981

Abstract

A second series of hybrid cells with sputter-deposited Cu/sub 2/S layers has been fabricated. An efficiency of about 4 3/4%, without antireflection coating, was achieved for one of the cells. This result approaches the 5 3/4% which was achieved in the first set (different Cu/sub 2/S deposition conditions) and confirms the viability of the sputtering process for this application. Significant progress has been made in fabricating all-sputtered cells with CdS layers deposited by planar magnetron reactive sputtering. Efficiencies of approximately 3%, without antireflection coatings, have been achieved in the as-deposited state for seven cells. Individual cells have yielded a J/sub sc/ of 12 mA/cm/sup 2/, a V/sub oc/ of 0.53V, and a fill factor of 0.72. Taken together these parameters would yield an efficiency of 4 1/2%. A strong coupling is found between the properties of the Cu/sub 2/S and CdS layers. However, the conditions which maximize J/sub sc/, V/sub oc/ and the fill factor do not appear to be mutually exclusive. Reflectance measurements indicate that 30% or more of the incident radiation is being reflected from the front surface of the cells over the wavelength range of the solar spectrum. Thus optimization of the cell parameters with a suitablemore » antireflection coating should yield cell efficiencies of about 6%. Characterization of the junctions formed in the all-sputtered cells under near-optimum deposition conditions indicates that they have remarkable properties in their as-deposited state, being very similar to high performance conventional cells after heat treatment. Junction ideality factors are about unity in the light, with J/sub 0/ values of about 2 x 10/sup -8/ mA/cm/sup 2/. Interface recombination velocities are as low as a few times 10/sup 5/ cm/sec. CdS depletion layer widths are about 2000 nm in the dark and collapse to about 200 nm under illumination.« less

Authors:
; ;
Publication Date:
Research Org.:
Solar Energy Research Inst., Golden, CO (USA); TELIC Corp., Santa Monica, CA (USA)
OSTI Identifier:
5618874
Report Number(s):
SERI/PR-9296-T2
ON: DE82006851
DOE Contract Number:
AC02-77CH00178
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; CADMIUM SULFIDE SOLAR CELLS; ELECTRIC CURRENTS; SPUTTERING; COPPER SULFIDES; ANTIREFLECTION COATINGS; DEPLETION LAYER; DESIGN; EFFICIENCY; ELECTRIC POTENTIAL; FABRICATION; FILL FACTORS; HETEROJUNCTIONS; MAGNETRONS; OPTIMIZATION; PHOTOLUMINESCENCE; RECOMBINATION; REFLECTIVITY; CHALCOGENIDES; COATINGS; COPPER COMPOUNDS; CURRENTS; DIRECT ENERGY CONVERTERS; ELECTRON TUBES; ELECTRONIC EQUIPMENT; EQUIPMENT; JUNCTIONS; LAYERS; LUMINESCENCE; MICROWAVE EQUIPMENT; MICROWAVE TUBES; OPTICAL PROPERTIES; PHOTOELECTRIC CELLS; PHOTOVOLTAIC CELLS; PHYSICAL PROPERTIES; SEMICONDUCTOR JUNCTIONS; SOLAR CELLS; SOLAR EQUIPMENT; SULFIDES; SULFUR COMPOUNDS; SURFACE PROPERTIES; TRANSITION ELEMENT COMPOUNDS; 140501* - Solar Energy Conversion- Photovoltaic Conversion

Citation Formats

Thornton, J.A., Anderson, W.W., and Meakin, J.D. Cadmium sulfide/copper sulfide heterojunction cell research by sputter deposition. Quarterly technical progress report, March 1, 1981-June 30, 1981. United States: N. p., 1981. Web. doi:10.2172/5618874.
Thornton, J.A., Anderson, W.W., & Meakin, J.D. Cadmium sulfide/copper sulfide heterojunction cell research by sputter deposition. Quarterly technical progress report, March 1, 1981-June 30, 1981. United States. doi:10.2172/5618874.
Thornton, J.A., Anderson, W.W., and Meakin, J.D. Sat . "Cadmium sulfide/copper sulfide heterojunction cell research by sputter deposition. Quarterly technical progress report, March 1, 1981-June 30, 1981". United States. doi:10.2172/5618874. https://www.osti.gov/servlets/purl/5618874.
@article{osti_5618874,
title = {Cadmium sulfide/copper sulfide heterojunction cell research by sputter deposition. Quarterly technical progress report, March 1, 1981-June 30, 1981},
author = {Thornton, J.A. and Anderson, W.W. and Meakin, J.D.},
abstractNote = {A second series of hybrid cells with sputter-deposited Cu/sub 2/S layers has been fabricated. An efficiency of about 4 3/4%, without antireflection coating, was achieved for one of the cells. This result approaches the 5 3/4% which was achieved in the first set (different Cu/sub 2/S deposition conditions) and confirms the viability of the sputtering process for this application. Significant progress has been made in fabricating all-sputtered cells with CdS layers deposited by planar magnetron reactive sputtering. Efficiencies of approximately 3%, without antireflection coatings, have been achieved in the as-deposited state for seven cells. Individual cells have yielded a J/sub sc/ of 12 mA/cm/sup 2/, a V/sub oc/ of 0.53V, and a fill factor of 0.72. Taken together these parameters would yield an efficiency of 4 1/2%. A strong coupling is found between the properties of the Cu/sub 2/S and CdS layers. However, the conditions which maximize J/sub sc/, V/sub oc/ and the fill factor do not appear to be mutually exclusive. Reflectance measurements indicate that 30% or more of the incident radiation is being reflected from the front surface of the cells over the wavelength range of the solar spectrum. Thus optimization of the cell parameters with a suitable antireflection coating should yield cell efficiencies of about 6%. Characterization of the junctions formed in the all-sputtered cells under near-optimum deposition conditions indicates that they have remarkable properties in their as-deposited state, being very similar to high performance conventional cells after heat treatment. Junction ideality factors are about unity in the light, with J/sub 0/ values of about 2 x 10/sup -8/ mA/cm/sup 2/. Interface recombination velocities are as low as a few times 10/sup 5/ cm/sec. CdS depletion layer widths are about 2000 nm in the dark and collapse to about 200 nm under illumination.},
doi = {10.2172/5618874},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Aug 01 00:00:00 EDT 1981},
month = {Sat Aug 01 00:00:00 EDT 1981}
}

Technical Report:

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  • Photoluminescence spectral measurements on 6000 nm thick reactive sputtered CdS coatings have yielded exciton and green edge emission spectra which are similar in their general character to those recorded from the evaporated CdS that yields high performance cells. The photoluminescence spectra of the sputtered coatings will be correlated with the performance of these materials when used for cells. All-sputter-deposited cells with composite doped and undoped CdS layers have yielded J/sub sc/ approx. 3 mA/cm/sup 2/. This is the highest J/sub sc/ that has been achieved for cells with this structure, which is designed to increase the junction electric field. Amore » hybrid cell with sputtered Cu/sub 2/S deposited onto evaporated CdS supplied by IEC has yielded J/sub sc/ approx. 18 mA/cm/sup 2/ (under illumination of 87.5 mW/cm/sup 2/), V/sub oc/ 0.47V, FF = 0.60, and eta = 5.74% with no AR coating. Cu/sub 2/S reactive sputtering experiments have further elucidated the influence of cathode and wall conditioning on the deposition process. CdS reactive sputtering experiments using a planar magnetron source have been initiated. Data are reported on the dependence of the deposition rate and coating resistivity on the substrate temperature and H/sub 2/S injection rate. The planar magnetron data are generally consistent with data previously reported for CdS reactive sputtering using cylindrical-post magnetrons. The resistivities of CdS coatings deposited using the planar magnetron are typicaly a factor of from three to ten lower than for coatings deposited using the cylindrical magnetrons. An analysis is reported which relates the frequency dispersion observed in C-V measurements on CdS/Cu/sub 2/S solar cells to the surface resistivity of the Cu/sub 2/S layer.« less
  • Photoluminescence measurements of sputter-deposited CdS films have been made. In a first series of tests thin films of both doped and undoped CdS, deposited under reactive sputtering conditions typical of those used in previous cell fabrication, were found to be void of any photoluminescence emission in the visible spectrum. Subsequent tests of thicker films deposited under various conditions have shown emission from the undoped, but not from the doped, material. A post-deposition treatment process, where CdS films are cooled following deposition in a flux of sputtered Cd, has proven to be the most effective method examined for producing off-stoichiometric coatingsmore » with low resistivities (< 100 ..cap omega..-cm). The treated films are found to exhibit a photoluminescence emission. The modified apparatus with the vacuum interlock, that was assembled during the previous program, has permitted more controlled studies to be made on the influence of cathode and wall conditioning in the Cu/sub 2/S reactive sputtering process. Experiments are reported which show that the conditioning times for achieving consistent Cu/sub 2/S coatings are considerably longer than had previously been expected. The deposition of Cu/sub 2/S coatings with consistent properties has been achieved, and hybrid cells have been fabricated with sputtered Cu/sub 2/S deposited onto evaporated CdS supplied by IEC. A first series of cells have yielded J/sub sc/ approx. 13 mA/cm/sup 2/, V/sub oc/ = 0.46 V, FF = 0.46, and eta = 2.7% after heat treatment at approx. 150/sup 0/C in Ar and H/sub 2/. These results, though preliminary, indicate that optimization of the composition and thickness of the sputtered Cu/sub 2/S should yield cells with efficiencies equivalent to those obtained with conventional ion exchange processing methods.« less
  • Extensive studies of the equilibration of wall and cathode surfaces in the reactive sputtering of Cu in Ar + H/sub 2/S atmospheres have provided guidelines for depositing Cu/sub x/S films with properties suitable for CdS/Cu/sub 2/S heterojunction fabrication. Hybrid cells which combine sputter-deposited Cu/sub 2/S with evaporated CdS and (CdZn)S have been fabricated. A CdS/Cu/sub 2/S cell with no antireflection coating has yielded a J/sub sc/ of 17.2 mA/cm/sup 2/ and an efficiency of 4.8% after heat treatment. A similar (CdZn)S/Cu/sub 2/S cell with an antireflection coating has yielded a J/sub sc/ of 18.5 mA/cm/sup 2/ and an efficiency ofmore » 7.2%. Significant progress has been made in fabricating all-sputtered cells with CdS layers deposited by planar magnetron reactive sputtering. Efficiencies of 3% or greater, without antireflection coatings, have been achieved for thirteen cells in their as-deposited state. Best individual cell parameters imply an efficiency of about 4.7%. Reflectance measurements indicate that 30% or more of the incident radiation is reflected from the front surface of the cells over the wavelength range of the solar spectrum. The conditions which maximize J/sub sc/, V/sub oc/, and FF do not appear to be mutually exclusive. Optimization of the cell parameters and the addition of a suitable AR coating should yield efficiencies in excess of 6%. The cells show that Cu/sub 2/S/CdS junctions equivalent to those formed by the topotaxial ion exchange method can be formed by sequential all-vacuum deposition of CdS and Cu/sub 2/S and that magnetron sputtering does not cause damage that compromises their electrical performance. An analysis is reported which examines the contribution of the spatially varying steady state majority carrier concentration to the frequency dispersion which is often observed in C-V junction measurements.« less
  • Progress has been made on improving the photon efficiency of the planar CdS/Cu/sub 2/S solar cell. Current in excess of 20 mA/cm/sup 2/ have been achieved. Mixed sulfide solar cells responsive to heat treatment are now being produced. The morphology of the Cu/sub 2/S/CdZnS junction has been examined and found to be significantly different than the morphology on CdS/Su/sub 2/S cells. Efficiencies measured under ELH simulation approaching 8% have been achieved. Work in the analytical task has focused on establishing the experimental techniques to study the trap levels in the CdS and to provide a working model for the voltagemore » instabilities in some (CdZn)S/Cu/sub 2/S cells. Cells under roof top exposure continue to be monitored.« less
  • Progress has been made on improving the photon efficiency of the planar CdS/Cu/sub 2/-S solar cell. Currents in excess of 20 mA/cm/sup 2/ have been achieved. Mixed sulfide solar cells responsive to heat treatment are now being produced. The morphology of the Cu/sub 2/S/CdZnS junction has been examined and found to be significantly different than the morphology on CdS/Cu/sub 2/S cells. Efficiencies measured under ELH simulation approaching 8% have been achieved. Work in the analytical task has focused on establishing the experimental techniques to study the trap levels in the CdS and to provide a working model for the voltagemore » instabilities in some (CdZn)S/Cu/sub 2/S cells. Cells under roof top exposure continue to be monitored.« less