Beyond Conventional Enhancements: Self‐Organization of a Buffer Material on Tin Oxide as a Game‐Changer for Improving the Performance of Inverted Organic Solar Cells

Abstract Inverted organic solar cells (OSCs) have garnered significant interest due to their remarkable stability. In this study, the efficiency and stability of inverted OSCs are enhanced via the in situ self‐organization (SO) of an interfacial modification material Phen‐NaDPO onto tin oxide (SnO ₂ ). During the device fabrication, Phen‐NaDPO is spin‐coated with the active materials all together on SnO ₂ . Driven by the interactions with SnO ₂ and the thermodynamic forces due to its high surface energy and the convection flow, Phen‐NaDPO spontaneously migrates to the SnO ₂ interface, resulting in the formation of an in situ modification layer on SnO ₂ . This self‐organization of Phen‐NaDPO not only effectively reduces the work function of SnO ₂ , but also enhances the ordered molecular stacking and manipulates the vertical morphology of the active layer, which suppress the surface trap‐assisted recombination and minimize the charge extraction. As a result, the SO devices based on PM6:Y6 exhibit significantly improved photovoltaic performance with an enhanced power conversion efficiency of 17.62%. Moreover, the stability of the SO device is also improved. Furthermore, the SO ternary devices based on PM6:D18:L8‐BO achieved an impressive PCE of 18.87%, standing as one of the highest values for single‐junction inverted organic solar cells to date.