Researchers at the Chinese Academy of Sciences, University of Chinese Academy of Sciences, University of Science and Technology Beijing, Guangxi University and Beijing University of Technology have developed a dual-molecule surface passivation strategy that significantly improves both the efficiency and operational stability of wide-bandgap (WBG) perovskite solar cells.
Wide-bandgap perovskites, typically incorporating ≥20% bromine in APb(I1−xBrx)3, are essential for tandem solar cells but suffer from small grain sizes, high densities of grain boundaries, and interfacial defects. These structural limitations accelerate non-radiative recombination and degradation under heat, light, and moisture, ultimately limiting performance and long-term stability. Despite rapid progress - power conversion efficiencies (PCEs) exceeding 27% within 15 years - these devices still fall short of the Shockley–Queisser limit by around 4%, largely due to interfacial losses.
To address these challenges, the team focused on engineering the perovskite/electron transport layer (ETL) interface using a synergistic combination of phenethylammonium iodide (PEAI) and propane-1,3-diammonium diiodide (PDAI2). Unlike conventional approaches that rely on forming 2D (PEA)2PbI4 layers held together by weak van der Waals and π–π interactions, this strategy introduces strong ionic bonding at the perovskite surface and grain boundaries.
This molecular design fundamentally alters the interfacial chemistry. The presence of PDAI2 suppresses the formation of the less stable (PEA)2PbI4 phase and instead promotes the formation of a PDAPbI4-based 2D perovskite phase. Due to stronger ionic interactions, the interlayer spacing is reduced to approximately 10 Å, enabling more efficient charge transport compared to conventional 2D structures with larger spacing. At the same time, both PEAI and PDAI2 interact with undercoordinated Pb2+ ions and iodide vacancies, effectively passivating defects and suppressing non-radiative recombination.
In addition to defect passivation, the dual-molecule treatment improves energy level alignment at the perovskite/ETL interface, facilitating charge extraction and reducing open-circuit voltage (Voc) losses. The result is enhanced carrier mobility, reduced hysteresis, and improved overall device performance.
Devices incorporating this dual passivation approach achieved a PCE of 23.54% with a high Voc of 1.26 V. Notably, the strategy also delivers substantial gains in stability. Unencapsulated devices retained more than 95% of their initial efficiency after 1200 hours under ISOS-L-1 continuous illumination conditions, and over 90% after 1085 hours at 65 °C in a nitrogen atmosphere.
Importantly, the improved environmental resistance is attributed to the robust ionic bonding introduced by PDAI2, which enhances tolerance to moisture, oxygen, and thermal stress - addressing a key limitation of PEAI-only treatments.
Overall, this work demonstrates that carefully designed dual-molecule surface passivation can simultaneously optimize interfacial energetics, suppress phase instability, and improve charge transport. The approach provides a viable pathway toward high-performance and durable WBG perovskite solar cells, with clear relevance for next-generation tandem photovoltaic technologies.
