Silver Pastes: Extending the Limits

Reprinted with permission from pv magazine

Silver pastes: A committee of the industry association SEMI is looking at how to reduce the amount of silver used in photovoltaic cells. Stephan Raithel of the SEMI PV Group as well as Weiming Zhang and David P. McMullen of Heraeus Precious Metals report on the goals, the approaches, and the achievements.

PV manufacturing is primarily cost driven. Within the latest edition of the International Technology Roadmap for PV (www.ITRPV.net) a detailed analysis of the strongest cost drivers along the supply chain has been conducted. When looking at the individual process steps the main elements driving the overall costs are throughput, productivity, depreciation, floor space, materials/consumables, utilities, waste disposal, labor, and cost of yield loss. Assuming that throughput and productivity of state-of-the-art machinery is very competitive, the differentiation
for each production step can be identified by an in-depth analysis of the named primary cost elements. The chart “Analysis of cost elements along the supply chain (see below right) shows the current situation of these positions for crystallization, wafering, cell and module production according to an analysis of existing production lines. Silver (Ag) and aluminium pastes are named in section 4 as very significant cost drivers in the cell manufacturing process. Therefore paste consumption needs to be reduced in a first step. The chart “Silver per cell” (see page 68) shows the Technology Roadmap’s estimations for the reduction of silver for 156 x 156 mm² cells.

Right now an active task force of the SEMI China Standards committee, with members from Suntech, Heraeus, Dupont, Ritech, Ferro, Tianwei New Energy, and Yingli Solar, is working on a SEMI standard that ensures a smoother discussion among manufacturers and paste suppliers. The first step is to identify the areas that could be standardized – such as definitions, terminology and testing methods.  (Click here to view the rest of the article as a PDF.)