Challenges of lowering solar cell production costs by reducing silver content in back side pastes

For mass production of crystalline silicon solar cells, one can adopt two schools of thought when the goal is to improve the overall value of the finished product: increasing the overall efficiency and thus power output of the finished cells, or rather provide an equal power conversion efficiency while using less costly materials to construct the cell. While the choice of either option is based in each individual business ideology, we will discuss herein how the latter goal can be achieved by reducing the costly silver usage in back contact interconnect pastes. Standard back contact patterns can have a wide variety of designs depending on the exact technology (full bus bars, solder pads, etc.); however there is the necessary evil that a considerable quantity of silver must be deposited to provide an ideal solder joint. The recent rise in the cost of silver has sparked urgency to reduce its usage, and thus this work will demonstrate that it is possible to reduce the amount of silver in back contact pastes by as much as 30% or more relative to current commercially-available pastes. As is typical of engineering new products with such large generational leaps, many challenges must be overcome to ensure that the resulting low silver containing pastes will support the long module lifetimes promised by manufacturers. These testing procedures and methods of data analysis will be discussed.