A custom-designed molecular layer using phenothiazine boosts tin perovskite solar cell efficiency by fixing interface mismatches.
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Tin perovskite solar cells have shown an abundance of potential. But their inefficiencies are holding them back. Recently published in Advanced Energy Materials, researchers have made progress in solving this issue by engineering a better molecular foundation for these cells.
An international team, led by scientists at Helmholtz-Zentrum Berlin, has found a way to reduce energy losses in a key internal layer of tin perovskite solar cells. Their solution is a self-assembled monolayer built from phenothiazine, a sulfur-containing molecule that has a much more snug alignment with the tin perovskite crystal structure.
That improved alignment means fewer electrons get lost at the interface between layers, boosting their effectiveness. The result is a lead-free solar cell with an efficiency of 8.2 %, outperforming earlier tin devices that used conventional contact layers.
We have demonstrated that the performance of tin perovskite photovoltaics can be significantly enhanced through targeted and rational molecular design.
Dr. Artem Musiienko, Principal Investigator, Helmholtz-Zentrum Berlin
SAMs in Tin Perovskites
The lowest contact layer in tin perovskite solar cells is usually PEDOT:PSS. It's time-consuming and expensive to create this layer. However, in lead perovskites, the PEDOT:PSS layer can be replaced with a more elegant solution: self-organized monolayers (SAMs), which have resulted in new record efficiencies.
Previous research using SAMs based on the MeO-2PACz compound in tin perovskites has shown inferior results compared to those with PEDOT:PSS.
The HZB team, working with chemists at Kaunas University of Technology in Lithuania, zeroed in on why. Using density functional theory, they showed that a common SAM molecule, MeO-2PACz, creates a misaligned interface when paired with tin perovskites, undermining performance. So they've created their new material.
Th-2EPT, a molecule based on phenothiazine with thiophene head groups, when used as an SAM, allows for the growth of tin perovskite films with excellent optoelectronic quality. The grains are smaller than those grown on PEDOT, but they are better connected and less prone to recombination losses, where electrons fall back into place before doing useful work.
We prove that the higher performance stems from the excellent optoelectronic quality of perovskite grown on the novel SAM.
Valerio Stacchini, Study First Author, Helmholtz-Zentrum Berlin
This development could dramatically improve current tin perovskite solar cells. In doing so, they could provide a less toxic answer to today's silicon-perovskite combinations.
Journal Reference:
Stacchini, V., et al. (2025) Phenothiazine-Based Self-Assembled Monolayer with Thiophene Head Groups Minimizes Buried Interface Losses in Tin Perovskite Solar Cells. Advanced Energy Materials. doi.org/10.1002/aenm.202500841.