Modifications of Textured Silicon Surface Morphology and Its Effect on Poly-Si/SiO _x Contact Passivation for Silicon Solar Cells

Journal Article · 01 November 2019 · IEEE Journal of Photovoltaics

DOI: https://doi.org/10.1109/JPHOTOV.2019.2937230 · OSTI ID:1573202

Kale, Abhijit ^[1]; Nemeth, William M ^[2]; Guthrey, Harvey L  ^[2]; Page, Matthew ^[2]; Al-Jassim, Mowafak M ^[2]; Young, David L ^[2]; Agarwal, Sumit ^[2]; Stradins, Pauls ^[2]

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1. National Renewable Energy Laboratory (NREL), Golden, CO (United States); Colorado School of Mines, Golden, CO (United States)
2. National Renewable Energy Laboratory (NREL), Golden, CO (United States)

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.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
• Grant/Contract Number: AC36-08GO28308
• OSTI ID: 1573202
• Report Number(s): NREL/JA-5900-74648
• Journal Information: IEEE Journal of Photovoltaics, Journal Name: IEEE Journal of Photovoltaics Journal Issue: 6 Vol. 9; ISSN 2156-3381
• Publisher: IEEECopyright Statement
• Country of Publication: United States
• Language: English