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 across different solvents for both lead and tin perovskites, demonstrating the clear advantage of tin and of DMSO-free processing. As it is well known, ion migration is the main obstacle for stable perovskite solar cells and full commercialization of the technology,” Artem Musiienko, corresponding author of the research, told pv magazine.
The team said that the ion density was investigated in four solar cells, each fabricated with widely used perovskite compositions: one was a lead (Pb)-based 21.5%-efficient triple-cation perovskite solar cell, with a Cs0.05(MA0.02FA0.98)0.95Pb(I0.98Br0.02)3 composition, referred to as CsMAFAPbI3 in the study.
Another was a 14.2%-efficient device incorporating tin (Sn) with a 50:50 Pb-Sn ratio 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, referred to as FASnI3. The fourth was also FASnI3 but made without using dimethyl sulfoxide (DMSO) solvent, rather using a mixture of dimethylformamide (DMF) and 1,3-dimethyl-2-imidazolidinone (DMI) as an alternative, enabling a DMSO-free device. The Sn-based devices had efficiencies of 6.8% and 5.6%, respectively.
Musiienko explained that the DMF-DMI solvent was established in earlier 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 involved current density-voltage (J-V) 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 corroborate conclusions.
They found that the Pb-based perovskite solar cell contained “the highest ion densities exceeding 1017 cm–3.” The incorporation of Sn in the Pb–Sn sample slightly reduced the ion density to 9 × 1,016 cm3, while the Sn-based devices made with the DMSO solvent had a lower density of ions – 8.7 × 1016 cm3.
As for the Sn-based devices made with DMF-DMI solvent, they had the “lowest ion density of 2.2 × 1016 cm–3.” The researchers noted that this was “over 10-fold lower than that observed in Pb-based perovskites,” adding that the Sn-based samples showed “minimal ionic losses” and they maintained 80% of the initial power conversion efficiency after 600-hour aging tests.
“The next step is to reduce ionic losses further and to improve the long-term stability of tin-based perovskites under realistic operating conditions,” said Musiienko, adding that “significant effort” is going into raising device efficiency to approach the 27% efficiency levels reported for lead-based devices.
The team is also seeking more suitable interfaces and device architectures for tin perovskite devices. “We recently discovered that tin-based perovskite absorbers exhibit energy level positions that differ fundamentally 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 “fully automated, high-throughput laboratory to tailor, characterize, and optimize solar cell materials, assisted by artificial intelligence technologies such as machine learning models and large molecular foundation 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 supports a newly established Young Investigator Group that is led by Artem Musiienko.
The research work is presented in “Minimizing Ionic Losses in DMSO-Free Tin-Based Perovskite Solar Cells, which was recently published by ACS Energy Letters. The team included researchers from the University of Hong Kong.
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