A caesium chloride seed layer developed at the institute promotes more even perovskite growth on textured silicon, addressing a defect that had limited performance in solvent-free tandem cells.
A team at the Helmholtz-Zentrum Berlin (HZB) has developed a new method for depositing perovskite layers in tandem solar cells, addressing a defect problem that has limited efficiency in cells made using solvent-free manufacturing.
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Perovskite-silicon tandem cells are typically built with a self-assembled monolayer, or SAM, that handles charge transport between the two materials. On textured silicon, used to capture more light, this layer forms unevenly, creating interface defects and unwanted lead iodide formation that reduce cell performance. The HZB team found that inserting a thin caesium chloride seed layer between the SAM and the perovskite promotes more even crystal growth and larger grains, suppressing those defects. First author Viktor Škorjanc said the seed layer “enables uniform growth of perovskite layers on textured silicon,” addressing defects caused by uneven coverage of the hole transport layer.
The cells were built using vacuum co-evaporation, a solvent-free process already established in industries such as OLED display and microelectronics manufacturing. Unlike solution-based lab techniques, it transfers more readily to the large, textured silicon wafers used in commercial production. Researchers say solvent-free layers also tend to be more stable, addressing one of the central barriers to commercialising perovskite solar cells.
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The cells made with the new method set a new efficiency mark, reaching 30.3 percent in the lab with 29.7 percent independently certified. The work builds on HZB’s earlier record of 29.15 percent, achieved in January 2020 and published in the journal Science. (TF)
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