Given the high percentage of metal cost in cell processing and concerns due to increasing Ag prices, alternative metallization schemes are being considered. Ni-Cu based front side metallization offers potential advantages of finer grid lines, lower series resistance, and reduced costs. A brief overview of various front side patterning techniques is presented. Subsequently, working principle of various plating techniques is discussed. For electroless plated Ni seed layer, fill factor values nearing 80% and efficiencies close to 17.5% have been demonstrated, while for Light Induced Plating deposited layers, an efficiency of 19.2% has been reported. Various methods for qualifying adhesion and long term stability of metal stack are discussed. Adhesion strengths in the range of 1–2.7？N/mm have been obtained for Ni-Cu contacts tabbed with conventional soldering process. Given the significance of metallization properties, different methods for characterization are outlined. The problem of background plating for Ni-Cu based metallization along with the various methods for characterization is summarized. An economic evaluation of front side metallization indicates process cost saving of more than 50% with Ni-Cu-Sn based layers. Recent successful commercialization and demonstration of Ni-Cu based metallization on industrial scale indicate a potential major role of Ni-Cu based contacts in near future. 1. Introduction The present solar PV market is growing at a rate of 35–40% per year and is one of the important renewable energy sources for non-CO2 energy in the future [1]. The rapid decline in the cost per watt has promoted increased deployment, hence nearing the tipping point of grid parity. Given the improving efficiencies of leading technologies, the focus should be to reduce the cost of various system components from wafer to balance of system components [1]. The cell processing typically contributes around 16-17% of the total system cost [2], while the contribution of metallization to the cell processing is around 40% due to the expensive Ag paste [3]. As shown in , the mass of Ag required in the front grid is inversely proportional to the acceptable fractional resistive losses due to front side metallization, irrespective of the finger design [4]. Equation is obtained from , where is substituted in terms of from [4]. Hence the amount of Ag required will double for decrease in acceptable resistive losses by 50%. In addition, due to presence of voids and additional constituents in screen-printed Ag contacts, typical product value is around 1.875, which further
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