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Solar Energy Materials & Solar Cells 94 (2010) 2094–2101

Contents lists available at ScienceDirect

Solar Energy Materials & Solar Cells
journal homepage: www.elsevier.com/locate/solmat

A novel two step metallization of Ni/Cu for low concentrator c-Si solar cells
Vikrant A. Chaudhari, Chetan S. Solanki n
Department of Energy Science and Engineering, Indian Institute of TechnologyBombay, Mumbai 400076, India

article info

abstract

Article history:
Received 13 January 2010
Received in revised form
20 May 2010
Accepted 25 June 2010
Available online 23 July 2010

In this work use of Ni/Cu double layers as front contact on commercial c-Si solar cells for low
concentration application is proposed. The front contact consists of Ni and Cu layers, which are
depositedusing electroless deposition and electroplating, respectively. These double layers of metals
help in reducing the series resistance of solar cells. Ni is deposited on Si wafers (solar cells processed up
to ARC deposition but without front contact), using Ni salt and a reducing agent in an electroless bath.
Further the Ni deposited wafers are annealed between temperatures 400 and 430 1C, toobtain NiSi
(nickel silicide), which lowers the contact resistivity between Ni and Si. Formation of NiSi and reduction
in contact resistivity are confirmed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy
(XPS) and transmission line model (TLM) analysis. Contact resistivity as low as 9 mO cm2 is achieved for
the annealed wafers. The NiSi layer is further electroplated with Cu toreduce metal grid line resistance.
A reduction in series resistance of about 50% as compared with commercial Ag screen printed solar cells
(series resistance approximately 40 mO) is achieved for the Ni/Cu plated front contact solar cells (series
resistance approximately 20 mO) of area 4 Â 4 cm2. I–V characteristic of these solar cells under 2–4 suns
concentration is measured and their performancecompared with those of commercial Ag screen
printed solar cells.
& 2010 Elsevier B.V. All rights reserved.

Keywords:
c-Si solar cells
Ni/Cu metallization
Electroplating
Low concentrator solar cells

1. Introduction
Typically, in commercial one sun c-Si solar cells the front
contact metallization is fabricated using screen printing of Ag
paste in an optimized grid pattern [1,2]. Thisprocess is
extensively used due to its high throughput and repeatability.
But these Ag screen printed solar cells are prone to reduction in
their efficiency when operated at concentration levels of more
than one sun. This reduction in efficiency can be attributed to high
series resistance primarily contributed by the front metal contact
areas (metal grid lines and metal–semiconductor contacts)[3,4].
The higher series resistance is due to low metal density in Ag
screen printed lines [5] and higher metal–semiconductor contact
resistivity, due to the presence of glass firth mostly contributed by
SiO2 in the Ag paste [6]. This results in an increased resistive
power loss under light concentration and eventually degrades the
solar cell efficiency [7]. Efforts are in progress to reducethe
resistivity of these contacts and thereby reduce the overall series
resistance of commercial c-Si solar cells and make them suitable
to operate at concentration levels more than one sun. Some of the
techniques implemented include use of hot melt paste [8] and Ag
electroplating of screen-printed grid [9]. These metallization
techniques reduce the series resistance of solar cells andimprove

n

Corresponding author. Tel.: +91 22 25767895; fax: +91 22 25764890.
E-mail address: chetanss@iitb.ac.in (C.S. Solanki).

0927-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.solmat.2010.06.032

their efficiencies. But these fabrication processes are complex,
which in turn increases the cost of metallization. In addition to
these techniques two...