German scientists have studied various ways to optimize the battery design of perovskite-silicon tandem products. In addition to the perovskite layer itself, they also pointed out several other areas that should be optimized for tandem cells, starting with silicon heterojunction processing. The study identified several ways to reduce battery production costs, including a significant reduction in indium consumption.
Perovskite-silicon tandem battery manufactured by HZB, Germany. The new research by Fraunhofer ISE examines the optimization of other battery processes that can be achieved by connecting batteries in series.
With the efficiency of the perovskite-silicon tandem cell approaching 30%, there is a strong interest in putting the technology into commercial production. A lot of work has been devoted to optimizing the perovskite layer itself for long-term performance and large-scale processing; now scientists are carefully studying how other important processes in silicon cell production will change when the deposition of the perovskite layer is added to the process.
A team led by the Fraunhofer Institute for Solar Energy Systems (ISE) in Germany focuses on transparent conductive oxide deposition and battery metallization. As people are increasingly concerned about the availability of the most commonly used indium and silver, these two stages in battery manufacturing are most in need of optimization.
The research starts with the process used in the manufacture of silicon heterojunction (HJT) cells and examines how the addition of a perovskite top cell will change the requirements for the rest of the cell structure. Their complete results can be found in the paper Optimized front TCO and metal grid electrode for module Integrated perovskite-silicon tandem solar cells published on Progress in Photovoltaics.
For transparent conductive oxide (TCO) layers usually made of indium tin oxide, the team found the potential to significantly reduce the amount of material used. The working current of the tandem cell is lower than that of silicon alone, and the refractive index of the perovskite top layer is lower than that of silicon, which means that TCO no longer needs to play an additional role as an anti-reflective coating. Based on this, the team speculates that the TCO thickness can be reduced from 75 nanometers to 20 nanometers, thereby reducing the cost of each battery by 0.0146 euros, or when the indium tin oxide is partially replaced by aluminum zinc oxide, the cost of each battery is reduced by 0.0079 euros .
For cell metallization, the team studied various possibilities of finger width and layout, and concluded that the number of wires required for interconnection can be reduced from 18 to 9 or even less, especially if it can be developed Copper plating solution for metallization. "For finger metallization with extremely low wire resistivity, this can be achieved by copper plating. Considering that the contact resistivity of the finger wire to the wire is low enough, it is possible to reduce to five wires," the team explained .
However, apart from this possibility, the group does not believe that series-connected batteries will significantly reduce silver consumption. Finally, they pointed out that for these two processes, the sensitivity of perovskite means that the production temperature needs to be lowered, from about 220 degrees Celsius currently used in HJT production to 130 degrees Celsius.
Overall, they found that by optimizing the TCO and metallization process, the perovskite-silicon tandem battery can reach an average power cost of 0.0751 euros/kWh, which is lower than the ISE's estimate of 0.0849 euros for today's single-junction PERC technology.
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