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Title: Modifications of Textured Silicon Surface Morphology and its Effect on Poly-Si/SiOx Contact Passivation for Silicon Solar Cells

Abstract

High-efficiency crystalline silicon (c -Si) solar cells require textured surfaces for efficient light trapping. However, passivation of a textured pyramidal surface to reduce carrier recombination is challenging due to the presence of sharp tips, edges, and valleys. Using electrical and surface microscopies combined with lifetime measurements, we report on the effect of HF:HNO3 etching on the pyramidal textured Si surface morphology, and on poly-Si/SiOx contact performance. Preferential rounding of either the valleys between pyramids, or the pyramid tips is obtained depending on the HF:HNO3 solution temperature. Both these morphologies make the pyramid shape irregular, with the pyramid faces no longer being predominantly a Si(111) surface. Our atomic force microscopy measurements further show that the nanoscale roughness over the pyramid face also reduces after HF:HNO3 etching. Thus, etching affects the microscopic pyramidal shape, the dominant crystallographic orientation, and the nanoscale roughness of the surface. We speculate that these three surface effects result in the improvement of surface passivation via poly-Si/SiOx contacts. However, this improved passivation is accompanied by increased reflectance of the HF:HNO3-etched textured surface. Finally, our electron-beam-induced current measurements reveal thickness nonuniformities in the thermally grown SiOx layer on the HF:HNO3-etched textured Si surface: SiO x is thicker near themore » pyramid tips, edges, and faces as compared with near the valleys between pyramids. This nonuniformity in the SiOx layer may explain the poorer passivation obtained on a KOH-textured and HF:HNO3-etched textured surface as compared with a planar surface.« less

Authors:
 [1];  [1]; ORCiD logo [1];  [1];  [1];  [1];  [1];  [1]
  1. National Renewable Energy Laboratory (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
OSTI Identifier:
1573202
Report Number(s):
NREL/JA-5900-74648
DOE Contract Number:  
AC36-08GO28308
Resource Type:
Journal Article
Journal Name:
IEEE Journal of Photovoltaics
Additional Journal Information:
Journal Volume: 9; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; atomic force microscopy; electron beam induced current; passivated contact; pyramid rounding; silicon solar cell

Citation Formats

Kale, Abhijit, Nemeth, William M, Guthrey, Harvey L, Page, Matthew, Al-Jassim, Mowafak M, Young, David L, Agarwal, Sumit, and Stradins, Pauls. Modifications of Textured Silicon Surface Morphology and its Effect on Poly-Si/SiOx Contact Passivation for Silicon Solar Cells. United States: N. p., 2019. Web. doi:10.1109/JPHOTOV.2019.2937230.
Kale, Abhijit, Nemeth, William M, Guthrey, Harvey L, Page, Matthew, Al-Jassim, Mowafak M, Young, David L, Agarwal, Sumit, & Stradins, Pauls. Modifications of Textured Silicon Surface Morphology and its Effect on Poly-Si/SiOx Contact Passivation for Silicon Solar Cells. United States. doi:10.1109/JPHOTOV.2019.2937230.
Kale, Abhijit, Nemeth, William M, Guthrey, Harvey L, Page, Matthew, Al-Jassim, Mowafak M, Young, David L, Agarwal, Sumit, and Stradins, Pauls. Fri . "Modifications of Textured Silicon Surface Morphology and its Effect on Poly-Si/SiOx Contact Passivation for Silicon Solar Cells". United States. doi:10.1109/JPHOTOV.2019.2937230.
@article{osti_1573202,
title = {Modifications of Textured Silicon Surface Morphology and its Effect on Poly-Si/SiOx Contact Passivation for Silicon Solar Cells},
author = {Kale, Abhijit and Nemeth, William M and Guthrey, Harvey L and Page, Matthew and Al-Jassim, Mowafak M and Young, David L and Agarwal, Sumit and Stradins, Pauls},
abstractNote = {High-efficiency crystalline silicon (c -Si) solar cells require textured surfaces for efficient light trapping. However, passivation of a textured pyramidal surface to reduce carrier recombination is challenging due to the presence of sharp tips, edges, and valleys. Using electrical and surface microscopies combined with lifetime measurements, we report on the effect of HF:HNO3 etching on the pyramidal textured Si surface morphology, and on poly-Si/SiOx contact performance. Preferential rounding of either the valleys between pyramids, or the pyramid tips is obtained depending on the HF:HNO3 solution temperature. Both these morphologies make the pyramid shape irregular, with the pyramid faces no longer being predominantly a Si(111) surface. Our atomic force microscopy measurements further show that the nanoscale roughness over the pyramid face also reduces after HF:HNO3 etching. Thus, etching affects the microscopic pyramidal shape, the dominant crystallographic orientation, and the nanoscale roughness of the surface. We speculate that these three surface effects result in the improvement of surface passivation via poly-Si/SiOx contacts. However, this improved passivation is accompanied by increased reflectance of the HF:HNO3-etched textured surface. Finally, our electron-beam-induced current measurements reveal thickness nonuniformities in the thermally grown SiOx layer on the HF:HNO3-etched textured Si surface: SiO x is thicker near the pyramid tips, edges, and faces as compared with near the valleys between pyramids. This nonuniformity in the SiOx layer may explain the poorer passivation obtained on a KOH-textured and HF:HNO3-etched textured surface as compared with a planar surface.},
doi = {10.1109/JPHOTOV.2019.2937230},
journal = {IEEE Journal of Photovoltaics},
number = 6,
volume = 9,
place = {United States},
year = {2019},
month = {9}
}