Modulating Perovskite Surface Energetics Through Tuneable Ferrocene Interlayers for High-Performance Perovskite Solar Cells.

Achieving rational control over chemical and energetic properties at the perovskite/electron transport layer (ETL) interface is crucial for realizing highly efficient and stable next-generation inverted perovskite solar cells (PSCs). To address this, we developed multifunctional ferrocene (Fc)-based interlayers engineered to exhibit adjustable passivating and electrochemical characteristics. These interlayers are designed to reduce non-radiative recombination, and to modulate the work function (WF) and uniformity of the perovskite surface, thereby enhancing device performance. The key role played by the highest occupied molecular orbital energies (E) of the Fc compounds relative to the perovskite valance band maximum (E) is revealed. This relationship is pivotal in controlling band bending and optimizing charge extraction. Notably, the conformationally flexible and more easily oxidized ferrocenyl-bis-furyl-2-carboxylate (2) is found to more effectively bind with undercoordinated Pb surface sites and modulate interfacial energetics, resulting in inverted PSCs achieving champion efficiencies of 25.16 %. These cells also displayed excellent stability, retaining >92 % of the initial efficiency after 1,000 h of maximum power point operation at 65 °C. By correlating the broadly tunable Fc-E with a decreased and homogenized perovskite surface WF, our work advances our understanding of Fc-based interlayers and opens new pathways for their application in high-efficiency solar technologies.