Side chain modulated ferrocene derivative as the interstitial conductive medium for high-performance and stable perovskite solar cells

The interfacial nonradiative recombination loss caused by the deep traps and mismatched band alignment restrained the commercial viability of perovskite solar cells (PSCs). Herein, we have constructed ferrocene carboxylic acid (FcA) and octafluoropentyl-ferrocenyl-carboxylate (OFFcA) interstitial conductive mediums to modulate the integral heterointerface properties and the photovoltaic performances of PSCs. By comparing the passivation strengths of the two molecules, we found that the synergistic effects among Fc/Fc⁺ redox shuttle, C=O group, and F substituents realize the optimal elimination of interfacial trap sources. Electron-withdrawing F groups reinforce the capacity of the Fc/Fc⁺ redox shuttle for the healing of metallic Pb defects and provide extensive anchoring sites to stabilize the organic components. Additionally, the homogeneity of the OFFcA layer as well as the humidity stability of perovskite film are facilitated through the introduction of F substituents, which reduce the contact resistance and improve the interfacial charge transfer. The champion OFFcA-modified device delivers an exceptional PCE of 23.62%, exceeding those of the control (PCE=22.32%) and FcA-modified (PCE=23.06%) devices. Moreover, the unencapsulated OFFcA-modified device retains 82.7% of the primary efficiency at 60% RH for more than 50 d and only loses less than 10% of the primary efficiency when stored in a glove box for more than 2000 h.