Well-defined covalent surface functionalization of diamond is a crucial, yet non-trivial, matter because of diamonds intrinsic chemical inertness and stability. Herein, we demonstrate a twostep functionalization approach for H-terminated boron-doped diamond thin films, which can lead to significant advances in the field of diamond hybrid photovoltaics. Primary diamond surface functionalization is performed via electrochemical diazonium grafting of in situ diazotized 4-iodoaniline. The freshly

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... afted iodophenyl functional moieties are then employed to couple a layer of thiophene molecules to the diamond surface via two wellestablished Pd-catalyzed cross-coupling reactions, i.e. Stille and Sonogashira. X-ray photoelectron spectroscopy analysis indicates a dense coverage and successful cross-coupling in both cases. However, we find that the Stille reaction is generally accompanied with severe surface contamination, in spite of process optimization and thorough rinsing. Sonogashira cross-coupling on the other hand provides a clean, high quality functionalization over a broad range of reaction conditions. The protocols employing Sonogashira reactions thus appear to be the method of choice toward future fabrication of high-performance dye-functionalized diamond electrodes for photovoltaic applications.