HANAU, Germany, Sept. 25, 2013 /PRNewswire/ -- High efficiency and low silver cost – a contradiction? Tests from the German based Institute for Solar Energy Research Hamelin (ISFH) show that it's not. The institute printed and tested a high efficiency solar cell (eta: 20.2%) with a silver cost less than $ 0.01 per Wp for front-side metallization using Heraeus pastes. This cell is a Passivated Emitter and Rear Cell (PERC) and the front-side grid was printed using the Dual Print technique.
Producing higher efficiency solar cells at a lower cost per Wp, that's the current objective and challenge of cell manufacturers. Metallization pastes for c-Si solar cells contain silver, due to this precious metal's excellent electrical, mechanical properties and performance in both cells and modules. However, silver is a costly material with a volatile price. New cell technologies and printing techniques help to reduce the amount of paste and thus the amount of silver required.
The tested, low silver cell from the ISFH combines PERC cell technology and Dual Printing. PERC cells feature a passivation layer on the back-side. Insulating the back-side helps gain higher V[OC] and J[SC] values and thushigher efficiencies. In Dual Print, a conventional firing-through front-side paste for the finger lines and a low activity paste for the floating busbars are printed using two separate steps. For the ISFH project, Heraeus' SOL9610 Series was applied as finger paste in stencil printing. The floating busbars were screen printed using SOL325A. SOL325A, as a low activity paste (also called non contacting paste), does not penetrate the passivation layer in order to connect to the emitter. SOL325A also features a lower silver content than the finger paste, which helps to reduce silver cost.
How can front-side metallization, with a silver cost of below 0.01 $ per Wp be achieved? Less than 70 mg of Ag metallization paste containing less than 55 mg of pure silver was required for printing both finger lines and busbars. With a performance of 4.82 Wp per cell and assuming a silver price of 670 $/kg, we calculate a silver cost for front-side metallization of less than 0.01 $ per Wp. Demonstrating a cell efficiency of 20.2% shows that you don't need to sacrifice performance for a low silver usage and cost.
Low silver metallization cost will be a major topic at the Heraeus Photovoltaics Business Unit booth at this year's EU PVSEC exhibition, to be held in Paris from October 1-3 (EU PVSEC Conference: September 30 – October 4). To discuss this topic with our experts and to learn more about Heraeus' metallization pastes, visit us at EU PVSEC trade show in Paris, Parc des Expositions Paris Nord Villepinte, in hall 2, booth number 2/C3 or go to www.pvsilverpaste.com.
