Researchers from Huazhong University of Science and Technology, Chinese Academy of Sciences, Wuhan University, DR Laser Technology (Wuxi), Hubei Optical Fundamental Research Center and Optics Valley Laboratory have developed a dipole-engineered passivation strategy that significantly boosts the performance and operational stability of all-perovskite tandem solar cells.
All-perovskite tandem architectures are considered promising photovoltaic platforms, but the SnPb narrow-bandgap subcell - a crucial component determining tandem efficiency - is limited by severe surface defect-induced recombination at the perovskite/C₆₀ interface. These interfacial defects lead to both reduced open-circuit voltage and unstable long-term performance, with most devices maintaining stability for less than 800 hours. To address this bottleneck, the researchers introduced methylpyridinium iodide (AMPYI₂) molecules as dipole-active interfacial passivators.
By tuning the methyl substitution position (ortho-, meta-, or para-) on the pyridinium ring, they precisely controlled the molecular dipole moment and binding affinity. Among the isomers, the ortho-substituted 2‑AMPYI₂ exhibited the largest dipole moment and strongest adsorption to both the SnPb perovskite surface and the C₆₀ electron transport layer. This strong dipole-induced field-effect passivation reduced the defect density at the interface by approximately two orders of magnitude, thereby suppressing non-radiative recombination and enhancing carrier extraction.
Single-junction SnPb perovskite solar cells employing 2‑AMPYI₂ achieved an impressive power conversion efficiency (PCE) of 23.3%, while maintaining 90% of the initial performance after 410 hours of operation at room temperature under maximum power point tracking. Extending this strategy to all-perovskite tandem devices yielded a record PCE of 28.5%, with a high open-circuit voltage of 2.16 V. The encapsulated tandem cells demonstrated excellent durability, retaining 90% efficiency over 892 hours at room temperature and 228 hours at 65 °C, marking a fourfold improvement in operational stability compared with control samples.
This dipole-mediated passivation approach demonstrates a generalizable framework for enhancing both efficiency and stability in tin–lead–based perovskites - paving the way toward scalable, high-performance all-perovskite tandems for real-world photovoltaic deployment.
