Researchers from the Federal Laboratories for Materials Science and Technology (EMPA), in Switzerland, have demonstrated a four-terminal tandem mini-module based on perovskite and copper, indium, gallium and selenium (CIGS) with an aperture area of around 2 cm2, and a geometric fill factor of over 93%.
“The key to the development of efficient flexible perovskite-CIGS thin-film tandem modules is the development of near-infrared (NIR) transparent perovskite solar modules on a flexible polymer foil,” the research's corresponding author, Fan Fu, told pv magazine. “Researchers in the Laboratory for Thin Films and Photovoltaics at Empa have overcome the challenges of laser patterning on flexible substrates to realize the first all-laser scribed monolithically interconnected NIR-transparent perovskite mini-modules on polymer film.”
The perovskite mini-module used in the tandem panel was fabricated on a flexible polyethylene napthalathe (PEN) substrate mounted to a glass substrate in a p–i–n device architecture. This configuration, according to the research team, shows reduced absorption in the NIR region.
The scientists used thermally evaporated buckminsterfullerene, a molecule which is also known as C60, for the fabrication of the electron transport layer (ETL). To protect the underlying layers from ion damage during the sputtering of transparent conductive oxide (TCO), they placed a tin(IV) oxide (SnO2) buffer layer on top of the C60 by atomic layer deposition (ALD). They also applied P2 scribing to create a pathway to interconnect the adjacent subcells and P3 scribing to isolate the rear electrode between the subcells.
The mini-module has a power conversion efficiency of 10.8% and an average transmittance of over 75% in the NIR range, which makes it suitable for tandem applications. “The light-harvesting potential of the NIR-transparent mini-module can be improved by utilizing a thicker wide-bandgap (WBG) perovskite absorber with excellent optoelectronic properties,” the academics said.
The perovskite module was combined with a CIGS module with an efficiency of 15.1%. “The flexible 4T perovskite-CIGS mini-module performs at an efficiency of 18.4% and outperforms both the perovskite and CIGS stand-alone mini-module,” the Swiss group emphasized. “An absolute efficiency gain of 7.5% and 3.3% is achieved with respect to the perovskite and CIGS stand-alone mini-modules.”
The Swiss Scientists present their findings in “Laser patterned flexible 4T perovskite-CIGS tandem minimodule with over 18% efficiency,” which was recently published in Solar RRL. “The flexible perovskite-CIGS tandem mini-modules can potentially be used in applications where flexibility and lightweight are important considerations, such as portable and wearable electronics, building- and vehicle-integrated photovoltaics (BIPV and VIPV), internet of things (IoT), and space applications,” Fu concluded.
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