UCLA researchers and Midsummer, a Swedish building-integrated PV (BIPV) module manufacturer, claim to have demonstrated a four-terminal (4T) tandem solar cell. It is based on a top cell made of perovskite and a bottom cell relying on copper, indium, gallium and selenium (CIGS).
“The cell is based on a perovskite top cell that has been optimized for integration with Midsummer’s CIGS cells that are utilized in their commercial suite of BIPV products,” said Midsummer, without revealing any additional technical details. “The research continues with the aim of a two-terminal perovskite-CIGS cell which will render this particular solar cell highly competitive and suitable for mass production.”
The manufacturer said the tandem cell is suitable for its Duo production equipment, which manufactures 56 mm x 156 mm CIGS cells on a flexible stainless steel substrate.
UCLA set an initial efficiency record for such tandem cells in 2018, at 22.4%. This surpassed the 17.8% efficiency achieved in 2016 by a collaboration of European research institutes, which developed a peroskite/CIGS mini-module measuring 3.76cm².
The US researchers designed the bottom cell as having an indium zinc oxide (IZO) transparent conductive oxide film, a tin(IV) oxide (SnO2) buffer layer, a perovskite layer, and a layer of methyl-substituted carbazole (Me-4PACz) as the hole-transport layer. For the top cell, they used an indium tin oxide (ITO) substrate, a cadmium sulfide (Cds) layer, and a CIGS absorber.
Yang Yang, a UCLA professor of materials science, said at the time that devices with similar designs could reach efficiencies above 30%.
“We feel fortunate to be working with Professor Yang’s group at UCLA which has demonstrated key advances in perovskites,” said Leon Chiu, president of Pioneer Materials, which is a key supplier for compound sputtering targets used in Midsummer’s novel processing for CIGS on stainless steel. “Integrating Midsummer’s production proven CIGS processing with Yang’s Lab tailored perovskite shows a clear path toward expanding the reach of BIPV by improving efficiency and lowering costs.”
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