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Title: Optimization of Open Circuit Voltage in Amorphous Silicon Solar Cells with Mixed-Phase (Amorphous+Nanocrystalline) p-type Contacts of Low Nanocrystalline Content

Abstract

No abstract prepared.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
915644
DOE Contract Number:
AC36-99-GO10337
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 11, 2007; Related Information: Article No. 114301
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; ELECTRIC POTENTIAL; OPTIMIZATION; SILICON SOLAR CELLS; Solar Energy - Photovoltaics

Citation Formats

Pearce, J. M., Podraza, N., Collins, R. W., Al-Jassim, M. M., Jones, K. M., Deng, J., and Wronski, C. R. Optimization of Open Circuit Voltage in Amorphous Silicon Solar Cells with Mixed-Phase (Amorphous+Nanocrystalline) p-type Contacts of Low Nanocrystalline Content. United States: N. p., 2007. Web. doi:10.1063/1.2714507.
Pearce, J. M., Podraza, N., Collins, R. W., Al-Jassim, M. M., Jones, K. M., Deng, J., & Wronski, C. R. Optimization of Open Circuit Voltage in Amorphous Silicon Solar Cells with Mixed-Phase (Amorphous+Nanocrystalline) p-type Contacts of Low Nanocrystalline Content. United States. doi:10.1063/1.2714507.
Pearce, J. M., Podraza, N., Collins, R. W., Al-Jassim, M. M., Jones, K. M., Deng, J., and Wronski, C. R. Mon . "Optimization of Open Circuit Voltage in Amorphous Silicon Solar Cells with Mixed-Phase (Amorphous+Nanocrystalline) p-type Contacts of Low Nanocrystalline Content". United States. doi:10.1063/1.2714507.
@article{osti_915644,
title = {Optimization of Open Circuit Voltage in Amorphous Silicon Solar Cells with Mixed-Phase (Amorphous+Nanocrystalline) p-type Contacts of Low Nanocrystalline Content},
author = {Pearce, J. M. and Podraza, N. and Collins, R. W. and Al-Jassim, M. M. and Jones, K. M. and Deng, J. and Wronski, C. R.},
abstractNote = {No abstract prepared.},
doi = {10.1063/1.2714507},
journal = {Journal of Applied Physics},
number = 11, 2007,
volume = 101,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The origin of the difference in the open circuit voltage V/sub oc/ between a p-i-n and n-i-p type hydrogenated amorphous silicon solar cells is discussed theoretically, considering the interaction of photogenerated free electrons and holes, i.e., the effect of a self-field. It has been clarified that the self-field aids the carrier collection in an n-i-p cell whereas it impedes the carrier collection in a p-i-n cell. This difference in the effect of the self-field on the photovoltaic process causes the difference in V/sub oc/ between these two type cells.
  • Data are presented showing that boron carryover into the i layer is responsible for the commonly observed difference in open circuit voltage between p-i-n and n-i-p amorphous silicon solar cells. It is proposed that the lower voltage samples are being limited by surface recombination at the p/i interface and that boron carryover reduces this recombination current. The V/sub oc/ is then able to rise to the point where it is limited by the bulk recombination current.
  • Local open-circuit voltage (Voc) distributions on amorphous and nanocrystalline mixed-phase silicon solar cells were measured using a scanning Kelvin probe microscope (SKPM) on the p layer of an n-i-p structure without the top ITO contact. During the measurement, the sample was illuminated with a laser beam that was used for the atomic force microscopy (AFM). Therefore, the surface potential measured by SKPM is the sum of the local Voc and the difference in workfunction between the p layer and the AFM tip. Comparing the SKPM and AFM images, we find that nanocrystallites aggregate in the amorphous matrix with an aggregationmore » size of {approx}0.5 ..mu..m in diameter, where many nanometer-size grains are clustered. The Voc distribution shows valleys in the nanocrystalline aggregation area. The transition from low to high Voc regions is a gradual change within a distance of about 1 ..mu..m. The minimum Voc value in the nanocrystalline clusters in the mixed-phase region is larger than the Voc of a nc-Si:H single-phase solar cell. These results could be due to lateral photo-charge redistribution between the two phases. We have also carried out local Voc measurements on mixed-phase SiGe:H alloy solar cells. The magnitudes of Voc in the amorphous and nanocrystalline regions are consistent with the J-V measurements.« less
  • By combining SKPM and AFM, they have developed a method to measure the local V{sub oc} distribution in mixed-phase solar cells. The results clearly show the nanocrystalline aggregation. The V{sub oc} is smaller in the nanocrystalline aggregates than in the surrounding amorphous matrix, and the transition from the low to high V{sub oc} is a gradual change. Although there are some lateral charge redistributions, a clear distinction between the amorphous and nanocrystalline regions has been observed. The current SKPM results and previous C-AFM results provide extra support for the two-diode model for explaining the carrier transport in the mixed-phase solarmore » cells.« less
  • Local open-circuit voltage (V{sub oc}) distributions on amorphous and nanocrystalline mixed-phase silicon solar cells were measured using a scanning Kelvin probe microscope (SKPM) on the p layer of an n-i-p structure without the top ITO contact. During the measurement, the sample was illuminated with a laser beam that was used for the atomic force microscopy (AFM). Therefore, the surface potential measured by SKPM is the sum of the local V{sub oc} and the difference in workfunction between the p layer and the AFM tip. Comparing the SKPM and AFM images, we find that nanocrystallites aggregate in the amorphous matrix withmore » an aggregation size of {approx}0.5 {micro}m in diameter, where many nanometer-size grains are clustered. The V{sub oc} distribution shows valleys in the nanocrystalline aggregation area. The transition from low to high V{sub oc} regions is a gradual change within a distance of about 1 {micro}m. The minimum V{sub oc} value in the nanocrystalline clusters in the mixed-phase region is larger than the V{sub oc} of a nc-Si:H single-phase solar cell. These results could be due to lateral photo-charge redistribution between the two phases. We have also carried out local V{sub oc} measurements on mixed-phase SiGe:H alloy solar cells. The magnitudes of V{sub oc} in the amorphous and nanocrystalline regions are consistent with the J-V measurements.« less