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Title: Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization

Abstract

An evaporated Al layer is known as an excellent rear metallization for highly efficient solar cells, but suffers from incompatibility with a common solder process. To enable solar cell-interconnection and module integration, in this work the Al layer is complemented with a solder stack of TiN/Ti/Ag or TiN/NiV/Ag, in which the TiN layer acts as an Al diffusion barrier. X-ray photoelectron spectroscopy measurements prove that diffusion of Al through the stack and the formation of an Al{sub 2}O{sub 3} layer on the stack's surface are responsible for a loss of solderability after a strong post-metallization anneal, which is often mandatory to improve contact resistance and passivation quality. An optimization of the reactive TiN sputter process results in a densification of the TiN layer, which improves its barrier quality against Al diffusion. However, measurements with X-ray diffraction and scanning electron microscopy show that small grains with vertical grain boundaries persist, which still offer fast diffusion paths. Therefore, the concept of stuffing is introduced. By incorporating oxygen into the grain boundaries of the sputtered TiN layer, Al diffusion is strongly reduced as confirmed by secondary ion mass spectroscopy profiles. A quantitative analysis reveals a one order of magnitude lower Al diffusion coefficientmore » for stuffed TiN layers. This metallization system maintains its solderability even after strong post-metallization annealing at 425 °C for 15 min. This paper thus presents an industrially feasible, conventionally solderable, and long-term stable metallization scheme for highly efficient silicon solar cells.« less

Authors:
; ; ; ;  [1]
  1. Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, 79110 Freiburg (Germany)
Publication Date:
OSTI Identifier:
22597814
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 120; Journal Issue: 2; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ALUMINIUM; ALUMINIUM OXIDES; ANNEALING; DEPLETION LAYER; DIFFUSION BARRIERS; GRAIN BOUNDARIES; ION MICROPROBE ANALYSIS; IONS; MASS SPECTROSCOPY; OXYGEN; PASSIVATION; SCANNING ELECTRON MICROSCOPY; SILICON SOLAR CELLS; SPUTTERING; SURFACES; TEMPERATURE RANGE 0400-1000 K; TITANIUM NITRIDES; X-RAY DIFFRACTION; X-RAY PHOTOELECTRON SPECTROSCOPY

Citation Formats

Kumm, J., Samadi, H., Chacko, R. V., Hartmann, P., and Wolf, A., E-mail: andreas.wolf@ise.fraunhofer.de. Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization. United States: N. p., 2016. Web. doi:10.1063/1.4954684.
Kumm, J., Samadi, H., Chacko, R. V., Hartmann, P., & Wolf, A., E-mail: andreas.wolf@ise.fraunhofer.de. Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization. United States. doi:10.1063/1.4954684.
Kumm, J., Samadi, H., Chacko, R. V., Hartmann, P., and Wolf, A., E-mail: andreas.wolf@ise.fraunhofer.de. Thu . "Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization". United States. doi:10.1063/1.4954684.
@article{osti_22597814,
title = {Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization},
author = {Kumm, J. and Samadi, H. and Chacko, R. V. and Hartmann, P. and Wolf, A., E-mail: andreas.wolf@ise.fraunhofer.de},
abstractNote = {An evaporated Al layer is known as an excellent rear metallization for highly efficient solar cells, but suffers from incompatibility with a common solder process. To enable solar cell-interconnection and module integration, in this work the Al layer is complemented with a solder stack of TiN/Ti/Ag or TiN/NiV/Ag, in which the TiN layer acts as an Al diffusion barrier. X-ray photoelectron spectroscopy measurements prove that diffusion of Al through the stack and the formation of an Al{sub 2}O{sub 3} layer on the stack's surface are responsible for a loss of solderability after a strong post-metallization anneal, which is often mandatory to improve contact resistance and passivation quality. An optimization of the reactive TiN sputter process results in a densification of the TiN layer, which improves its barrier quality against Al diffusion. However, measurements with X-ray diffraction and scanning electron microscopy show that small grains with vertical grain boundaries persist, which still offer fast diffusion paths. Therefore, the concept of stuffing is introduced. By incorporating oxygen into the grain boundaries of the sputtered TiN layer, Al diffusion is strongly reduced as confirmed by secondary ion mass spectroscopy profiles. A quantitative analysis reveals a one order of magnitude lower Al diffusion coefficient for stuffed TiN layers. This metallization system maintains its solderability even after strong post-metallization annealing at 425 °C for 15 min. This paper thus presents an industrially feasible, conventionally solderable, and long-term stable metallization scheme for highly efficient silicon solar cells.},
doi = {10.1063/1.4954684},
journal = {Journal of Applied Physics},
number = 2,
volume = 120,
place = {United States},
year = {Thu Jul 14 00:00:00 EDT 2016},
month = {Thu Jul 14 00:00:00 EDT 2016}
}