A new class of acceptor-substituted S,N-heteropentacenes is developed for vacuum-processed organic solar cells, providing encouraging power conversion efficiencies of up to 6.5%. Atomic force microscopy (AFM) investigations give a direct correlation between the blend film morphology and the photovoltaic parameters, such as short-circuit current density (JSC ) and fill factor (FF).

The Stille coupling method was used to functionalize the 5‐ and 6‐positions of 1,10‐phenanthroline with thiophene substituents. Photophysical investigations of 5,6‐bis(5‐methylthien‐2‐yl)‐1,10‐phenanthroline showed a marked influence of the substituents on the absorption properties, as a bathochromic shift of 50 nm regarding the π–π* transitions was observed. The contribution of the substituents in the corresponding Ru complex, in turn, was negligible on the absorption properties of the compound, while the extinction coefficient for the complex dropped by a factor of 0.5 compared to reference complexes. Structural investigation of the ligand and the complex revealed a perpendicular orientation of the thiophene groups with respect to the phenanthroline plane, while no preferred conformation of sulfur atoms (parallel or antiparallel) could be observed. The newly synthesized complex exhibits a superior photostability relative to [Ru(bpy)3]2+, which is promising for future applications.

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Acceptor-substituted S,N-heteropentacenes with systematically varied alkyl side chains were prepared and implemented as donors in vacuum-processed OSCs giving devices with efficiencies in the range of 4–6%. An odd–even effect with respect to the length of the alkyl side chains is noted.