A research team led by the Chinese Academy of Sciences’ Institute of Physics has developed a sandwich-like buffer layer to improve the performance and scalability of semi-transparent CsPbI3-based perovskite solar cells and four-terminal (4T) tandem solar cells.
The MoOx/Ag/MoOx (MAM) buffer layer consists of a thin layer of silver (Ag) between molybdenum oxide (MoOx) layers that can act as the front cell window layer in semi-transparent CsPbI3 solar cells and 4T stacked cells.
The scientists explain that, compared to conventional MoOx layers, the MAM acts as an effective buffer layer by enhancing carrier transportation and collection capabilities. The team attributes this improvement to the in-situ formation of Ag2MoO4 in the MAM sandwich structure.
The scientists fabricated a semi-transparent CsPbI3 device with an aperture area of 0.50 cm2 that encompassed a MAM buffer layer and TOPCon bottom cell with edge passivation. This device demonstrated a power conversion efficiency of 18.86%. A corresponding 4T CsPbI3/TOPCon tandem solar cell then achieved an efficiency of 26.55%.
The MAM buffer layer’s scalability was tested by developing CsPbI3 perovskite minimodules with an efficiency of 16.67% and 4T CsPbI3/TOPCon tandem minimodules with an efficiency of 26.41%, at an aperture area of 6.62 cm2. The research team remarked that this is the first reported minimodule demonstration for this architecture.
The device’s stability was also tested, with the transparent CsPbI3 perovskite minimodules retaining over 93% of the initial performance after more than 1,000 hours of storage.
The researchers say this work establishes a universal strategy for MAM sandwich-structured buffer layers for semi-transparent CsPbI3 perovskite solar cells across small sizes to large sizes, which is also suitable for tandem solar cells.
“This kind of scalable sandwich-like architecture not only expands the design flexibility of functional layers in perovskites and tandem solar cells, but also offers a promising pathway for further efficiency enhancement,” they added.
The academics involved will now work on finding suitable transparent, photostability materials to draw the two devices together in series, in particular for large-size tandem modules, while considering practical application scenarios that control costs. This will include experimenting with alternatives to silver, as it is a relatively costly metal.
Their findings are presented in the research paper “Designing MoOX/Ag/MoOX sandwich structured buffer layer for four-terminal CsPbI3/TOPCon tandem minimodules,” available in the journal Materials Futures.
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