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Australian scientists claim to have achieved the highest efficiency recorded to date in a perovskite-CIGS tandem solar cell built on a flexible steel substrate. In the proposed cell configuration, the steel can act as both a substrate and an electrode.
A group of scientists led by the University of Sydney has manufactured a tandem photovoltaic cell based on copper, indium, gallium and selenium (CIGS) and perovskite thin film technology. The device uses a flexible steel substrate instead of glass.
The advantage of this flexible and conductive steel substrate is that the steel itself can act as a substrate and electrode to manufacture cells with one or several junctions, whether monolithic with a large surface area or singular ones with a smaller surface area.
The new cell is an evolution of a 17.1% efficient perovskite device that another research group at the University of Sydney presented in August. “There is no reason why perovskite-based tandem devices cannot also be demonstrated on steel substrates,” lead author of the research Anita Ho-Baillie told pv magazine . “To date, there is only one demonstration of a flexible perovskite-CIGS tandem solar cell, with an efficiency of 13.2%, on a 30 µm thick polyimide flexible sheet substrate.”
The research group constructed the cell with a 50 µm thick steel substrate coated with molybdenum (Mo), a CIGS absorber, a cadmium sulfide (CdS) window layer, transparent conductive oxide films of zinc oxide doped with aluminum (AZO), a hole transport layer (HTL) based on nickel(II) oxide (NiO), a perovskite absorber, an electron transport layer (ETL) based on buckminsterfullerene (C60), a spacer based in phenyl-C61-butyric acid (PCB), an indium tin oxide (ITO) layer and an anti-reflective layer.
The scientists deposited the perovskite layer using thermal evaporation and spin coating. “As the substrate used is conductive, metallic contact with the rear face of the lower CIGS cell can be made on both sides of the substrate, allowing flexibility for the interconnection of the cells,” they explained.
Tested under standard lighting conditions, the tandem cell achieved a power conversion efficiency of 18.1%, an open circuit voltage of 1,645 mV, a short circuit current density of 17.7 mA/cm2, and a 62% filling. This result represents the highest efficiency recorded to date in a flexible perovskite-CIGS tandem solar cell.
“The substrate used has the added advantage of being conductive, which allows metallic contacts to be established on both sides,” the researchers explain. “Physical deposition proves effective in overcoming the unique challenges associated with the irregular surfaces of CIGS cells for tandem demonstrations.”
They described the novel cell concept in the study “ Efficient Flexible Monolithic Perovskite-CIGS Tandem Solar Cell on Conductive Steel Substrate ,” recently published in ACS Energy Letters . |
