Double-Function Lewis-Base-Additive-Mediated Interfacial Configuration and Defect Mitigation in Perovskite Solar Cells

Interfacial defects and charge recombination are key barriers to achieving high performance and long-term stability in perovskite solar cells (PSCs). To address this, we developed a dual-functional interfacial engineering strategy using fluorescein disodium salt (FLNa₂), a Lewis-base-rich molecule that simultaneously passivates the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole-transport layer and the perovskite interface. This approach effectively neutralizes antisite defects in the perovskite, suppresses deep trap states, and minimizes nonradiative recombination. Consequently, it enhances interfacial contact, improves charge extraction, promotes perovskite crystallinity, suppresses pinhole formation, and increases the built-in potential. The incorporation of FLNa₂ into the device architecture leads to a notable ∼13.24% enhancement in the power conversion efficiency, underscoring the crucial role of oxygen–lead coordination in improving the HTL/perovskite interface. Furthermore, the trap density is significantly reduced in FLNa₂-5-modified devices, confirming the effective passivation of the defect states. These findings highlight the importance of molecular-scale defect modulation at functional interfaces and establish FLNa₂ as a promising multifunctional additive for advancing the efficiency and stability of next-generation perovskite photovoltaics.