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Title: Development of high-efficiency solar cells on silicon web. First quarterly progress report, April 20-July 15, 1984

Abstract

The major objective of the work reported is to improve web base material with a goal toward obtaining solar cell efficiencies in excess of 18% (AM1). The program consists of the investigation of carrier loss mechanisms in web silicon, development of techniques to reduce carrier recombination in web, and web cell fabrication using effective surface passivation. Web surfaces have been bevelled with the intention of measuring the electrical activity of the twin plane. Web crystals have been intentionally contaminated with vanadium and titanium to examine the twin-plane-assisted internal gettering by DLTS. Model calculations were done to see the effect of twin-plane activity on V/sub oc/ as a function of resistivity of the web material. Experiments were initiated to study the effect of heat treatment and gettering on the minority carrier diffusion length in webs. Fabrication of high-efficiency web cells using several web crystals was initiated. These cells will include surface passivation and double-layer antireflection coating. (LEW)

Authors:
; ; ;
Publication Date:
Research Org.:
Westinghouse Research and Development Center, Pittsburgh, PA (USA)
OSTI Identifier:
6509562
Report Number(s):
DOE/JPL/956786-84/1
ON: DE85001383
DOE Contract Number:
NAS-7-100-956786
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; SILICON SOLAR CELLS; HEAT TREATMENTS; MATHEMATICAL MODELS; TWINNING; DENDRITIC WEB GROWTH METHOD; DIFFUSION LENGTH; CRYSTAL GROWTH METHODS; DIMENSIONS; DIRECT ENERGY CONVERTERS; EQUIPMENT; LENGTH; PHOTOELECTRIC CELLS; PHOTOVOLTAIC CELLS; SOLAR CELLS; SOLAR EQUIPMENT; 140501* - Solar Energy Conversion- Photovoltaic Conversion

Citation Formats

Rohatgi, A., Meier, D.L., Campbell, R.B., and Rai-Choudhury, P. Development of high-efficiency solar cells on silicon web. First quarterly progress report, April 20-July 15, 1984. United States: N. p., 1984. Web. doi:10.2172/6509562.
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Rohatgi, A., Meier, D.L., Campbell, R.B., & Rai-Choudhury, P. Development of high-efficiency solar cells on silicon web. First quarterly progress report, April 20-July 15, 1984. United States. doi:10.2172/6509562.
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Rohatgi, A., Meier, D.L., Campbell, R.B., and Rai-Choudhury, P. Thu . "Development of high-efficiency solar cells on silicon web. First quarterly progress report, April 20-July 15, 1984". United States. doi:10.2172/6509562. https://www.osti.gov/servlets/purl/6509562.
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@article{osti_6509562,
title = {Development of high-efficiency solar cells on silicon web. First quarterly progress report, April 20-July 15, 1984},
author = {Rohatgi, A. and Meier, D.L. and Campbell, R.B. and Rai-Choudhury, P.},
abstractNote = {The major objective of the work reported is to improve web base material with a goal toward obtaining solar cell efficiencies in excess of 18% (AM1). The program consists of the investigation of carrier loss mechanisms in web silicon, development of techniques to reduce carrier recombination in web, and web cell fabrication using effective surface passivation. Web surfaces have been bevelled with the intention of measuring the electrical activity of the twin plane. Web crystals have been intentionally contaminated with vanadium and titanium to examine the twin-plane-assisted internal gettering by DLTS. Model calculations were done to see the effect of twin-plane activity on V/sub oc/ as a function of resistivity of the web material. Experiments were initiated to study the effect of heat treatment and gettering on the minority carrier diffusion length in webs. Fabrication of high-efficiency web cells using several web crystals was initiated. These cells will include surface passivation and double-layer antireflection coating. (LEW)},
doi = {10.2172/6509562},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Aug 09 00:00:00 EDT 1984},
month = {Thu Aug 09 00:00:00 EDT 1984}
}
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Technical Report:
View Technical Report (1.94 MB)
DOI:  10.2172/6509562
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  • ; ; ; ...
    The major objective of the work reported is to improve web base material with a goal toward obtaining solar cell efficiencies in excess of 18% (AM1). The program consists of the investigation of carrier loss mechanisms in web silicon, development of techniques to reduce carrier recombination in web, and web cell fabrication using effective surface passivation. The effect of stress on web cell performance has been investigated. Preliminary data indicate that stress has no appreciable influence on the minority-carrier diffusion length in the as-grown web crystals. A web solar cell manufacturing run has also been completed. Fill factors were lowmore » and cell efficiencies were only in the 13 to 15% range. The impurity-twin-plane interaction has been investigated by conducting DLTS measurements as a function of depth on titanium-doped web crystal. Initial results indicate that the grown-in titanium impurity tends to pile up near the twin plane. Electron beam induced current (EBIC) measurements have been performed on beveled web samples to detect any recombination activity at the twin planes within the web material. Preliminary measurements indicate that twin planes in web show higher recombination activity compared to the rest of the bulk; however, this recombination activity can vary appreciably along the length of the web crystal. (LEW)« less

  • ; ; ; ...
    The major objective of the work reported was to improve web base material with a goal of obtaining solar cell efficiencies in excess of 18% (AM1). Efforts were directed toward identifying carrier loss mechanisms in web silicon, eliminating or reducing these mechanisms, designing a high-efficiency cell structure with the aid of numerical models, and fabricating high-efficiency web solar cells. The defect which is primarily responsible for limiting the minority carrier diffusion length in dendritic web silicon solar cells was identified as a dislocation decorated with impurity precipitates. Low-energy hydrogen ion implantation was used to passivate the dislocation/precipitate defect in webmore » silicon cells. Cells were fabricated from dendritic web silicon with oxide surface passivation, aluminum back reflector, and double-layer antireflective coating. The highest efficiency obtained was 16.6%. (LEW)« less

  • ; ; ; ...
    During this period emphasis was placed on the development of process techniques that will enhance web cell performance. The oxidation conditons to passivate web cells were established to reduce surface recombination velocity. Evaporated double-layer antireflective coating using ZnSe and MgF/sub 2/ films was developed to minimize reflection losses from the front surface. An aluminum back-surface reflector was developed to utilize the unabsorbed long-wavelength photons. Web solar cells were also fabricated by incorporating the above advanced features. Efficiencies as high as 16.9% were obtained on 1 cm x 1 cm dendritic web silicon cells on 0.37 ohm-cm web crystals. A combinedmore » effect of oxide passivation, evaporated double-layer AR coating, and back-surface reflector gave approx. 59% improvement in the short-circuit current and 69% increase in cell efficiency compared to the counterpart baseline cell with no passivation, AR coating, or back-surface reflector. During this period low-resistivity web crystals (0.37 ohm-cm, crystal No. 4-275) were also grown to take advantage of heavy doping in the base. Reasonable diffusion lengths (approx. 150 ..mu..m) were obtained in the finished low-resistivity web cells, encouraging further investigation for achieving high efficiency in web cells.« less

  • ; ; ; ...
    This sixth quarterly report describes the results of cross-sectional TEM measurements along with LBIC and DLTS measurements on baseline high-efficiency and low-efficiency web cells. These techniques afford a means for examining the structural and electrical quality of the dendritic web silicon as a function of depth. The electrical activity of the twin planes is of particular interest. Also described are the results of hydrogen ion implantation into partially processed and into completed web cells in an effort to passivate defects. Other topics include the surface damage introduced by beveling web silicon with Syton, the achievement of hole diffusion lengths exceedingmore » 100 ..mu..m in relatively low-resistivity n-base cells, and the effect of significantly reducing the dissolved oxygen concentration of web material.« less

  • ; ; ; ...
    The objective of this program is to understand and improve web silicon so that high-efficiency web cells can be fabricated using advanced cell design and processing. It is clear that high efficiency is a major attribute that will enhance the large-scale applicability of phtotvoltaic systems. Systems calculations indicate that for very large-scale terrestrial applications, greater than or equal to 15% efficient photovoltaic modules will be required at a cost of less than or equal to 50c/watt. This implies that approx. 18% efficient cells will be needed at low cost. Dendritic web silicon is a single-crystal silicon ribbon that has greatmore » potential for low-cost and high-efficiency solar cells. The loss mechanisms in dendritic web silicon are studied by investigating the electrical activity of twin planes, the role of impurities and defects in web, impurity interaction with twin planes, starting web material quality, and the effect of heat treatment and gettering on web quality. An improved understanding of the above effects should lead to fabrication of approx. 18% efficient web cells with good uniformity. Progress toward the development of high-efficiency solar cells on web silicon is described. Reported here are the results of two solar runs using low-resistivity dendritic web silicon, which were completed this quarter. In addition to fabrication low-resistivity web solar cells, laser beam-induced current (LBIC) and DLTS measurements were done on beveled web surfaces to investigate the twin plane activity as well as the twin plane interaction with the impurity.« less