Interface engineering plays a decisive role in governing charge extraction, energetic alignment, and long-term stability in perovskite solar cells (PSCs). Building upon this framework, we report two newly designed fluorinated bathocuproine (BCP) derivatives—BCP-m2F and BCP-m4F—that incorporate site-selective mono-fluorination on the terminal phenyl units. These materials were developed as an extension of our previously reported BCP-m1, in which aryl substitution was introduced to enhance molecular planarity and improve charge-transport pathways. In contrast, the present work focuses on strategic fluorination as a means to simultaneously manipulate intermolecular interactions, interfacial energetics, and environmental robustness, while retaining the desirable structural motif of the parent BCP scaffold.

Electrochemical measurements reveal that the LUMO levels of BCP-m2F and BCP-m4F are nearly identical to each other and close to that of BCP-m1, indicating that fluorination does not significantly shift the electron-transport energy levels. Density functional theory calculations support this conclusion, predicting only minor modulation of the frontier orbitals, while suggesting a stronger noncovalent binding interaction with C60, attributed to F-induced polarization effects. These theoretical predictions are validated experimentally: BCP-m4F forms a more uniform and continuous interlayer on top of the C60 electron-transport layer, yielding films with improved conductivity and reduced interfacial resistance compared to BCP-m2F.

Comprehensive device and materials characterization further elucidate the advantages of fluorinated BCP derivatives. Time-resolved photoluminescence (TRPL) measurements indicate more efficient interfacial charge extraction and suppressed trap-assisted recombination when BCP-m4F is incorporated. J–V analysis confirms improved fill factor and reduced nonradiative Voc losses, consistent with reduced interfacial defect density. Contact angle measurements show that the fluorinated derivatives—particularly BCP-m4F—exhibit significantly enhanced surface hydrophobicity, contributing to improved resistance against moisture ingress. Under ISOS-D3 damp heat testing (85 °C, 85% RH), PSCs employing BCP-m4F maintain higher operational stability, demonstrating lower performance decay and suppressed interfacial degradation compared to both BCP-m2F and the previously reported BCP-m1.

Importantly, devices incorporating BCP-m4F show minimal open-circuit voltage loss under low-light and diffuse-light illumination, underscoring its advantageous energetic alignment and efficient carrier extraction in regimes dominated by trap-mediated recombination. This low-light robustness highlights the potential of BCP-m4F for indoor photovoltaic applications, where stability of Voc and suppression of interfacial losses are critical.

Collectively, this work demonstrates that combining rational backbone design with targeted mono-fluorination enables the creation of multifunctional electron-extraction interlayers that integrate enhanced film morphology, superior interfacial contact, improved environmental resistance, and stable energy alignment. These findings provide a generalizable design strategy for next-generation interfacial materials aimed at achieving high efficiency and long-term durability in perovskite solar cells.