Publication date: 15th December 2025
Stability remains an important challenge in metal halide perovskite solar cells, where performance degradation is often associated with interfacial processes occurring under thermal stress and moisture exposure. In particular, the interface between the electron transport layer and the metal electrode has been identified as a critical region influencing both operational stability and charge extraction. In this study, two site-selectively fluorinated bathocuproine (BCP) derivatives, BCP-m2F and BCP-m4F, are examined as interfacial buffer layers with the aim of evaluating their influence on interfacial properties and device stability.
The fluorinated BCP derivatives are compared with a previously reported aryl-substituted BCP derivative (BCP-m1). While fluorination induces only minor changes in energy-level alignment relative to the non-fluorinated reference, it leads to observable differences in film morphology and interfacial behavior. BCP-m4F forms relatively uniform films and exhibits higher electrical conductivity than BCP-m2F, which correlates with reduced trap-assisted recombination and more efficient charge extraction at the interface. These trends are supported by time-resolved photoluminescence measurements, J–V analysis, and impedance spectroscopy.
Interfacial wetting and moisture-related effects are further examined through contact angle measurements, indicating increased hydrophobic character for the fluorinated derivatives. Device stability is evaluated under damp heat conditions (ISOS-D3, 85 °C/85% RH), where devices incorporating BCP-m4F show slower performance degradation compared to those using non-fluorinated or differently fluorinated BCP derivatives. In addition, light-intensity-dependent measurements reveal that devices with BCP-m4F exhibit reduced open-circuit voltage loss under low-light conditions.
Overall, this study shows that site-selective fluorination of small-molecule buffer layers can affect interfacial morphology, charge recombination behavior, and environmental stability in metal halide perovskite solar cells. These observations provide experimental insight into how molecular-level modifications at interfacial layers relate to stability-related device characteristics.
H.N.T., D.Y., and D.-G.K. contributed equally to this work. J.-Y.S. is grateful to the Ministry of Trade, Industry and Energy (MOTIE) and Korea Institute for Advancement of Technology (KIAT) through the International Cooperative R&D program (P0026100) and Ministry of Science and ICT (MSIT) grant from the Korean Government (RS-2024-00406152). J.J. acknowledges the support of the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2023-00220748). This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP), the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (RS-2023-00303745). This research was supported by the 4th BK21 Education and Research Division for Energy Convergence Technology. Laser scribing system at Pusan National University was used in this work
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