Surface Stoichiometric Tuning for High‐Efficiency and Light Illumination Stability in Sn–Pb Perovskite Solar Cells by PbBr<sub>2</sub> Wet Surface Treatment

Md. Abdul Karim; Yulu He; Wasif Islam Chowdhury; Md. Emrul Kayesh; Towhid H. Chowdhury; Shamim Ahmmed; Takeaki Sakurai; Ashraful Islam

doi:10.1002/solr.202500225

Article Surface Stoichiometric Tuning for High‐Efficiency and Light Illumination Stability in Sn–Pb Perovskite Solar Cells by PbBr₂ Wet Surface Treatment

Md. Abdul Karim (Research Center for Energy and Environmental Materials (GREEN), National Institute for Materials Science (NIMS)) ; Yulu He ; Wasif Islam Chowdhury ; Md. Emrul Kayesh ; Towhid H. Chowdhury ; Shamim Ahmmed ; Takeaki Sakurai ; Ashraful Islam

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Md. Abdul Karim, Yulu He, Wasif Islam Chowdhury, Md. Emrul Kayesh, Towhid H. Chowdhury, Shamim Ahmmed, Takeaki Sakurai, Ashraful Islam. Surface Stoichiometric Tuning for High‐Efficiency and Light Illumination Stability in Sn–Pb Perovskite Solar Cells by PbBr₂ Wet Surface Treatment. Solar RRL. 2025, 9 (12), 2500225. https://doi.org/10.1002/solr.202500225

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Tin–lead (Sn–Pb) mixed perovskite solar cells (PSCs) are promising as bottom subcells in all-perovskite tandem solar cells, but the oxidation of Sn2+ remains challenging for long-term stability. This study reveals a compositional gradient in Sn–Pb perovskite films, where excess Sn ions accumulate at the surface, intensifying oxidation and recombination losses. To address this issue, we introduce a PbBr2-TOAB wet surface treatment strategy during the fabrication of Sn–Pb perovskite films. X-ray photoelectron spectroscopy analysis confirms that this treatment achieves more balanced Sn:Pb stoichiometry from~4.36:1 to ~2.74:1, ensuring improved film quality and resistance to Sn2+ oxidation. The treatment strategy boosts the power conversion efficiency (PCE) to
21.61% (0.09 cm2), with an independently certified (from the National Institute of Advanced Industrial Science and Technology) PCEof19.12%, compared to 21.13% for control PSCs. Moreover, target larger PSCs (1cm2) achieved an impressive PCE of 20.83%. The target PSCs show enhanced stability, retaining 80% of their initial PCE after 50 h of continuous light soaking. More importantly, encapsulated target PSCs maintain 95% of their initial PCE for 300s under continuous illumination at maximum power point tracking conditions. Time-dependent photoluminescence examination confirms that PbBr2-TOAB treatment significantly reduces ion migration, improving stability under light illumination.

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