A novel two step metallization of Ni/Cu for low concentrator c-Si solar cells

Abstract

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 deposited using 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 °C, to obtain 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 mΩ cm 2 is achieved for the annealed wafers. The NiSi layer is further electroplated with Cu to reduce 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 mΩ) is achieved for the Ni/Cu plated front contact solar cells (series resistance approximately 20 mΩ) of area 4×4 cm 2. I– V characteristic of these solar cells under 2–4 suns concentration is measured and their performance compared with those of commercial Ag screen printed solar cells.