Researchers in Germany have developed a DMSO-free manufacturing process for tin-based perovskite solar cells that dramatically reduces ion density – more than ten times lower than lead-based devices – leading to improved stability.
A research team led by researchers from Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) and the University of Potsdam in Germany has developed an alternative dimethyl sulfoxide (DMSO) process for tin-based perovskite solar cells, finding lower ion density compared to lead-based devices.
“Our study is the first to compare ionic degradation pathways between different solvents for both lead and tin perovskites, demonstrating the clear advantage of tin- and DMSO-free processing. As is known, ion migration is the main obstacle for stable perovskite solar cells and full commercialization of the technology,” said Artem Musiienko, corresponding author of the study. pv magazine.
The team said ion density was examined in four solar cells, each fabricated with commonly used perovskite compositions: one was a lead (Pb)-based 21.5% efficient tri-cation perovskite solar cell, with a Cs0.05(MA0.02FA0.98)0.95Pb(I0.98Br0.02)3 composition, called CsMAFAPbI3 in the study.
Another example was a 14.2% efficient device that incorporated tin (Sn) with a Pb-Sn ratio of 50:50 as the B-site cations in a (Cs0.1MA0.3FA0.6)(Pb0.5Sn0.5)I3 perovskite composition.
The third was a lead-free, Sn only, FA0.87PEA0.13SnI3 perovskite, also called FASnI3. The fourth was also FASnI3, but made without using dimethyl sulfoxide (DMSO) solvent, rather than using a mixture of dimethylformamide (DMF) and 1,3-dimethyl-2-imidazolidinone (DMI) as an alternative, allowing a DMSO-free device. The Sn-based devices had an efficiency of 6.8% and 5.6%, respectively.
Musiienko explained that the DMF-DMI solvent was developed in previous research as a stable processing route for tin perovskites as an alternative to DMSO, which he noted can cause oxidation of tin.
The scientists quantitatively measured the ion density and migration of ions in the material. It included current density-voltage (JV) measurements, fast hysteresis, bias-assisted charge extraction measurements, voltage-dependent photoluminescence transient measurements, and temperature-dependent fast hysteresis, as well as several other tests to confirm conclusions.
They found that the Pb-based perovskite solar cell contained “the highest ion densities above 1017 cm–3.” The incorporation of Sn into the Pb-Sn sample slightly reduced the ion density to 9 × 1016 cm3, while the Sn-based devices made with the DMSO solvent had a lower ion density: 8.7 × 1016 cm3.
The Sn-based devices made with DMF-DMI solvent had the “lowest ion density of 2.2 × 1016 cm–3.” The researchers noted that this was “more than 10 times lower than what was observed with Pb-based perovskites,” adding that the Sn-based samples showed “minimal ion losses” and that they retained 80% of the initial energy conversion efficiency after 600-hour aging tests.
“The next step is to further reduce ion losses and improve the long-term stability of tin-based perovskites under realistic operating conditions,” says Musiienko, adding that “significant efforts” are being made to increase device efficiency to approach the 27% efficiency levels reported for lead-based devices.
The team is also looking for more suitable interfaces and device architectures for tin-perovskite devices. “We recently discovered that tin-based perovskite absorbers exhibit energy level positions that are fundamentally different from those of lead-based systems,” Musiienko said.
To accelerate the development of suitable interface layers and selective contact materials, he noted that work is underway on a “high-throughput, fully automated laboratory to tailor, characterize and optimize solar cell materials, assisted by artificial intelligence technologies such as machine learning models and large molecular base model frameworks for inverse materials design.”
The project is funded by the German Federal Ministry of Research, Technology and Space (BMFTR) through the NanoMatFutur program, which is a newly established Young Investigator Group which is led by Artem Musiienko.
The research work is presented in “Minimizing ion losses in DMSO-free tin-based perovskite solar cellswhich was recently published by ACS Energy Letters. The team consisted of researchers from the University of Hong Kong.
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