Formation of Ultrathin and Highly Stable Aromatic Monolayers on Silver Surface─Three Legs Are Better Than One

Surface functionalization by self-assembled monolayers (SAMs) is a key method for controlling the morphology and electronic coupling of organic semiconductors (OSC) on metal electrodes in organic electronic and photovoltaic devices. For such applications, it is crucial to use ultrathin, and thus highly conducting, upright-oriented aromatic monolayers (compatible with OSC growth), which should also possess high thermal and chemical stability, to withstand both the OSC deposition procedure and heat dissipation during device operation. Following these criteria, we analyze here the thinnest possible aromatic SAMs on the most conductive metal electrode, silver. These SAMs are built from molecules with a thickness corresponding to a single phenyl ring and are designed using either traditional monodentate or triptycene-based, tridentate surface anchoring geometry. Spectroscopic analysis confirms, in both cases, the successful formation of well-defined, upright-oriented, and ultrathin (∼0.8 nm) aromatic monolayers, with all available anchoring groups bonded to the metal substrate, enabling direct comparison of both structural designs. Quantitative thermal and chemical stability analysis shows inferior characteristics for the standard monodentate anchoring design. In contrast, the application of triptycene-based tripods leads to the formation of ultrathin monolayers with high thermal and chemical stability, which is comparable to─or even greater than─that of significantly thicker monodentate SAMs. These monolayers thus meet the criteria for optimal interface engineering in organic electronics and photovoltaics, opening new opportunities for improved device performance.