Diels-Alder adduct formation at solid interfaces between fullerenes and acenes

Understanding organic-organic interfaces is rather challenging due to their large complexity regarding morphology, molecular orientation at the interface, interdiffusion, and energetics. One additional important but often neglected aspect are chemical reactions occuring at such interfaces. For solid interfaces between pentacene and Buckminster-Fullerene (C₆₀) recently very efficient Diels-Alder (D-A) adduct formation has been reported. Considering the importance of pentacene/C₆₀ as prototypical donor-acceptor combination to study fundamental processes in organic photovoltaics, understanding this effect is essential. In this work, we provide detailed NEXAFS-based investigations with respect to the temperature-dependence and reaction zone depth of this effect. Moreover, we widely vary the interface morphology and observe that the D-A adduct formation is most efficient for bulk heterojunctions of pentacene and C₆₀. By also investigating further material combinations such as PEN/C₆₀-PCBM and interfaces between C₆₀ and functionalized acenes, we observe trends for the occurrence of the D-A adduct formation correlated with the different chemical properties of the involved compounds.