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Title: Silicon solar cell process development, fabrication and analysis. Phase II. Annual report, 1 July 1979-30 June 1980

Abstract

Solar cells were fabricated from EFG (RH) ribbons from multiple dies, silicon on ceramic (SOC), dendritic web, cast silicon by HEM, and semi-continuous CZ from both VARIAN and HAMCO. Baseline and improved solar cells were made from the sheets. Baseline solar cells processed in both Phase I and Phase II, involving cells from EFG, SOC, dendritic web, and HEM, indicated that no significant improvement in silicon sheet quality has been achieved in Phase II. Solar cells from semi-continuous CZ showed cell performance close to the conventional CZ control cells, although the cells from the semi-continuous CZ have shown wider performance range because of variation in crystalline perfection. Generally, process upgrading provided improvement in cell performance, the improvement depending on the process used and the quality of the sheet silicon. Study of the effect of grain size on solar cell performance suggested that the minimum grain size to make solar cells of 10% AMO efficiency is about 500 ..mu..m, which is expected to provide minimum module efficiency of 10% AMI. If other harmful impurities are added in the process of sheet growth, the minimum grain size must be increased. The BSF study showed that the higher the resistivity of the startingmore » substrates, the greater the relative improvement in cell performance, probably because of greater shift in Fermi levels at the back L/H junction (pp+) and also because of the higher initial values of minority carrier diffusion length. This study also suggested that proper control of the back-surface field (BSF) process could minimize the junction shunting problems often introduced by the BSF processing.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Optical Coating Lab., Inc., City of Industry, CA (USA). Photoelectronics Div.
OSTI Identifier:
7017358
Report Number(s):
DOE/JPL/955089-80/4
DOE Contract Number:
NAS-7-100-955089
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; SILICON SOLAR CELLS; FABRICATION; PERFORMANCE; CZOCHRALSKI METHOD; DENDRITIC WEB GROWTH METHOD; DIPPED COATINGS; EFFICIENCY; EFG METHOD; ELECTRIC CONDUCTIVITY; ELECTRICAL PROPERTIES; EXPERIMENTAL DATA; FILL FACTORS; GRAIN SIZE; GRAPHS; HEAT EXCHANGER METHOD; IMPURITIES; SPECTRAL RESPONSE; TABLES; COATINGS; CRYSTAL GROWTH METHODS; CRYSTAL STRUCTURE; DATA; DIRECT ENERGY CONVERTERS; EQUIPMENT; INFORMATION; MICROSTRUCTURE; NUMERICAL DATA; PHOTOELECTRIC CELLS; PHOTOVOLTAIC CELLS; PHYSICAL PROPERTIES; SIZE; SOLAR CELLS; SOLAR EQUIPMENT; 140501* - Solar Energy Conversion- Photovoltaic Conversion

Citation Formats

Yoo, H.I., Iles, P.A., Ho, F.F., and Leung, D.C. Silicon solar cell process development, fabrication and analysis. Phase II. Annual report, 1 July 1979-30 June 1980. United States: N. p., 1980. Web. doi:10.2172/7017358.
Yoo, H.I., Iles, P.A., Ho, F.F., & Leung, D.C. Silicon solar cell process development, fabrication and analysis. Phase II. Annual report, 1 July 1979-30 June 1980. United States. doi:10.2172/7017358.
Yoo, H.I., Iles, P.A., Ho, F.F., and Leung, D.C. Tue . "Silicon solar cell process development, fabrication and analysis. Phase II. Annual report, 1 July 1979-30 June 1980". United States. doi:10.2172/7017358. https://www.osti.gov/servlets/purl/7017358.
@article{osti_7017358,
title = {Silicon solar cell process development, fabrication and analysis. Phase II. Annual report, 1 July 1979-30 June 1980},
author = {Yoo, H.I. and Iles, P.A. and Ho, F.F. and Leung, D.C.},
abstractNote = {Solar cells were fabricated from EFG (RH) ribbons from multiple dies, silicon on ceramic (SOC), dendritic web, cast silicon by HEM, and semi-continuous CZ from both VARIAN and HAMCO. Baseline and improved solar cells were made from the sheets. Baseline solar cells processed in both Phase I and Phase II, involving cells from EFG, SOC, dendritic web, and HEM, indicated that no significant improvement in silicon sheet quality has been achieved in Phase II. Solar cells from semi-continuous CZ showed cell performance close to the conventional CZ control cells, although the cells from the semi-continuous CZ have shown wider performance range because of variation in crystalline perfection. Generally, process upgrading provided improvement in cell performance, the improvement depending on the process used and the quality of the sheet silicon. Study of the effect of grain size on solar cell performance suggested that the minimum grain size to make solar cells of 10% AMO efficiency is about 500 ..mu..m, which is expected to provide minimum module efficiency of 10% AMI. If other harmful impurities are added in the process of sheet growth, the minimum grain size must be increased. The BSF study showed that the higher the resistivity of the starting substrates, the greater the relative improvement in cell performance, probably because of greater shift in Fermi levels at the back L/H junction (pp+) and also because of the higher initial values of minority carrier diffusion length. This study also suggested that proper control of the back-surface field (BSF) process could minimize the junction shunting problems often introduced by the BSF processing.},
doi = {10.2172/7017358},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 1980},
month = {Tue Jan 01 00:00:00 EST 1980}
}

Technical Report:

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  • Solar cells were fabricated from EFG ribbons (Mobil-Tyco), Dendritic webs (Westinghouse), Cast Ingots by Heat Exchanger Method (HEM, Crystal Systems), and Cast Ingots by Ubiquitous Crystallization Process (UCP, Semix). Baseline and other process variations were applied to fabricate solar cells. EFG ribbons grown in a carbon-containing gas atmosphere showed significant improvement in silicon quality. This new EFG demonstrated an average baseline efficiency of 10.3% as opposed to 8.0% AM1 for the earlier EFG. The best efficiency achieved by the advanced process was 13.8% under AM1 conditions. Baseline solar cells from dendritic webs of various runs indicated that the quality ofmore » the webs under investigation was not as good as the conventional CZ silicon, showing an average minority carrier diffusion length of about 60 ..mu..m versus 120 ..mu..m of CZ wafers.« less
  • Evaluation was performed for three sheet silicon forms: (a) continuous Czochralski growth (Varian), (b) EFG multi-ribbon (Resistance-heated), and (c) dendritic web silicon. AMO efficiencies (average) obtained were as follows: (efficiencies of control cells made from Czochralski silicon, processed alongside are in parentheses) (a) continuous Czochralski cells - 10.7% (10.9%); (b) EFG Cells: (i) Standard Process - 6.5% (approx. 12%), (ii) High Efficiency Process - 8.0% (>12%), and (c) Dendritic Web (Standard Process) - 10.1% (11.2%). In addition to the illuminated performance, the usual backup measurements were made of diffusion length, spectral response, dark diode characteristics, and fine light spot scanning.more » Early attempts to include BSF processes to low resistivity silicon led to excessive cell shunting; work proceeds to identify the reasons.« less
  • Progress in fabrication and characterization of solar cells from EFG ribbons and HEM ingots is reported. EFG ribbons grown in carbon-containing gas atmosphere showed improved sheet quality. This new EFG provided an average baseline cell efficiency of 10.3% under AM1 (as opposed to 8.0% for the earlier EFG). The best efficiency achieved by the advanced process was 13.8% AM1. Evaluation of two ingots from the HEM process indicated that HEM has a problem of inhomogeneity in sheet quality within each of the two ingots studied to data.
  • This program has investigated, developed and utilized technologies appropriate and necessary for improving the efficiency of solar cells made from various unconventional silicon sheets. During this reporting period, work has progressed in fabrication and characterization of solar cells from RTR ribbons (Motorola), EFG (RF and RH) ribbons (Mobil-Tyco), dendritic webs (Westinghouse), Silso wafers (Wacker), cast silicon by HEM (Crystal Systems), silicon on ceramic (Honeywell) and continuous Czochralski ingots (Hamco). Solar cells were fabricated using a standard process typical of those used currently in the silicon solar cell industry. Also back surface field (BSF) processing and other process modifications were includedmore » to give preliminary indications of possible improved performance. The parameters measured included open circuit voltage, short circuit current, curve fill factor, and conversion efficiency (all taken under AMO illumination). Also measured for typical cells were spectral response, dark I-V characteristics, minority carrier diffusion length, and photoresponse by fine light spot scanning. The results were compared to the properties of cells made from conventional single crystalline Czochralski silicon with an emphasis on statistical evaluation. Limited efforts were made to identify growth defects which will influence solar cell performance and discussion is given on the difficulties experienced in processing the sheets using near-conventional methods.« less
  • Solar cells have been fabricated from unconventional silicon materials supplied in the Large Area Sheet Task of the Low Cost Solar Array Project. The cells were constructed using methods intended to optimize the efficiency, as well as by a standard method intended to act as a baseline procedure. Following fabrication, all cells have been measured on the Spectrolab Solar Simulator at Air Mass Zero and 28/sup 0/C. Conversion efficiencies are based upon total device area. Maximum conversion efficiency obtained for Kayex continuous CZ material has been 12.4% (optimized), for Crystal Systems HEM material 11.2% (optimized), for Mobil Tyco EFG (RH)more » 8.4% (baseline) and EFG (RF) 9.8% (baseline), for Westinghouse Web material 12.0% (optimized), for Motorola RTR 7.2% (baseline), and for Wacker Silso 10.6% (baseline). All of these materials are from Phase I of the Contract. Phase II of the contract has started with Mobil-Tyco EFG (RH) material. Following fabrication by the baseline method this material, as well as the others in the program, will be fabricated using low-cost processing methods.« less