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Title: Distribution of Local Open-Circuit Voltage on Amorphous and Nanocrystalline Mixed-Phase Si:H and SiGe:H Solar Cells (Poster)

Abstract

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 solar cells.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
893111
Report Number(s):
NREL/PO-520-39865
TRN: US200625%%90
DOE Contract Number:
AC36-99-GO10337
Resource Type:
Conference
Resource Relation:
Conference: Prepared for the 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4), 7-12 May 2006, Waikoloa, Hawaii
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; DISTRIBUTION; ENERGY CONVERSION; SOLAR CELLS; TRANSPORT; SOLAR ENERGY; PV; PHOTOVOLTAIC; AMORPHOUS; NANOCRYSTALLINE; Solar Energy - Photovoltaics

Citation Formats

Jiang, C.-S., Moutinho, H. R., Al-Jassim, M. M., Kazmerski, L. L., Yan, B., Yang, J., and Guha, S. Distribution of Local Open-Circuit Voltage on Amorphous and Nanocrystalline Mixed-Phase Si:H and SiGe:H Solar Cells (Poster). United States: N. p., 2006. Web.
Jiang, C.-S., Moutinho, H. R., Al-Jassim, M. M., Kazmerski, L. L., Yan, B., Yang, J., & Guha, S. Distribution of Local Open-Circuit Voltage on Amorphous and Nanocrystalline Mixed-Phase Si:H and SiGe:H Solar Cells (Poster). United States.
Jiang, C.-S., Moutinho, H. R., Al-Jassim, M. M., Kazmerski, L. L., Yan, B., Yang, J., and Guha, S. Mon . "Distribution of Local Open-Circuit Voltage on Amorphous and Nanocrystalline Mixed-Phase Si:H and SiGe:H Solar Cells (Poster)". United States. doi:. https://www.osti.gov/servlets/purl/893111.
@article{osti_893111,
title = {Distribution of Local Open-Circuit Voltage on Amorphous and Nanocrystalline Mixed-Phase Si:H and SiGe:H Solar Cells (Poster)},
author = {Jiang, C.-S. and Moutinho, H. R. and Al-Jassim, M. M. and Kazmerski, L. L. and Yan, B. and Yang, J. and Guha, S.},
abstractNote = {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 solar cells.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2006},
month = {Mon May 01 00:00:00 EDT 2006}
}

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  • 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
  • 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
  • No abstract prepared.
  • We use conductive atomic force microscopy (C-AFM) to measure the local current flow in the mixed-phase hydrogenated silicon n-i-p solar cell structure without the top ITO contact. The forward biased C-AFM images reveal that for the fully amorphous region the current is very low on the entire surface. However, high current spikes appear in the mixed-phase region, where the current spikes are correlated to the formation of nanocrystallite aggregations with a diameter of {approx}500 nm. Furthermore, the density of the current spikes increases from the mixed-phase to the substantially nanocrystalline regions. The nanocrystallite aggregation supports our previously proposed parallel-connected two-diodemore » model for Voc drops with crystalline volume fraction and light-induced V{sub oc} increase in the mixed-phase solar cells. Adding a 50-nm thick a-Si:H buffer layer between the p and i layers significantly reduces the magnitude of the high current spikes, even the top morphology appears unaffected. This result is also consistent with the previously proposed two-diode model for explaining the carrier transport in the mixed-phase solar cells.« less
  • Chopped beam measurements indicate that the light generated current in a-Si:H p-i-n solar cells is voltage dependent, and passes through zero at the diffusion voltage V /SUB D/ . The authors' results and those of others indicate that V /SUB D/ is low, <1.1V, and hence the open circuit voltage is low. This analysis suggests that, the thin n- and p- contact regions have insufficient total charge to support the fields known to exist in the cells. Hence interface states and/or the contact materials are playing a significant role in determining the open circuit voltage of a-Si:H solar cells.