A research team led by Germany's Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) and the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia has fabricated a perovskite-silicon tandem solar cell using a two-step perovskite deposition method that is said to be compatible with industry-standard textured silicon.
The researchers explained that the novelty of their new tandem device is the high-quality surface passivation of the perovskite top cell, which enables its combination with a standard silicon bottom solar cell, whose texturization represents a problem for the deposition of the perovskite layer.
“So far, effective passivation has not been fully harnessed on textured perovskite silicon tandem solar cells, with prior success largely confined to flat-front architectures,” said the research's lead author, Oussama Er-Raji.
The silicon bottom cell was fabricated with a 250 μm-thick p-doped float-zone silicon wafer and an industrial double-sided random-pyramid texture with a pyramid size distribution ranging from 1 to 4 μm on both sides, where intrinsic/doped amorphous silicon passivation layers were deposited via plasma-enhanced chemical vapor deposition (PECVD).
The top perovskite solar cell was based on a hole transport layer (HTL) made of a phosphonic acid called methyl-substituted carbazole (Me-4PACz), a double halide perovskite absorber, a p-phenylenediaminium iodide (PDAI) passivation layer, and formamidinium cations.
The deposition of the passivation layer was carried out through spin-coating at 4000 rpm, followed by annealing at 100 C. The perovskite surface treatment was based on 1,3-diaminopropane dihydroiodide. “We have now managed excellent passivation by depositing 1,3-diaminopropane dihydroiodide on the uneven perovskite surface,” Er-Raji said.
Tested under standard illumination conditions, the tandem cell was able to achieve a power conversion efficiency of 33.1% and an open-circuit voltage of 2.01 V, while also showing an “extended” outdoor stability at a testing facility on the Red Sea coast.
“Surface passivation of solar cells is not just a nice-to-have feature; it is an essential booster for their efficiency and stability,” stated Stefan Glunz, Professor of Photovoltaic Energy Conversion at the University of Freiburg and Director of the Photovoltaics Division at Fraunhofer ISE. “For today’s silicon solar cells, surface passivation was the key for high efficiencies in industrial production, and it is encouraging that the PV industry will benefit from these positive effects for perovskite silicon tandem solar cells as well.”
The device was presented in the paper “Electron accumulation across the perovskite layer enhances tandem solar cells with textured silicon,” published in Science. The group included academics from the University of Freiburg in Germany.
“The researchers’ findings build on work in the Fraunhofer lighthouse project MaNiTU as well as the projects PrEsto and Perle, both funded by the Federal Ministry for Economic Affairs and Energy,” the Fraunhofer ISE said.
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