Effect of Meso‐ or β‐Functionalization of Porphyrins on the Photovoltaic Properties of Organic Solar Cells

Porphyrin derivatives are widely used as donors in organic solar cells (OSCs) due to their excellent optical and electrochemical properties. Although porphyrins can be functionalized at the meso‐ and β‐positions, only meso‐functionalized porphyrins have been reported as OSCs. Consequently, a direct comparison of the properties of porphyrins functionalized at these two positions is needed. The synthesis of two similar D–π–A–π–D materials is described herein and these compounds contain benzothiadiazole as the acceptor core and two Ni‐porphyrins as donors functionalized at the meso‐ and β‐positions to give RC19 and RC20 , respectively. The optical and electrochemical properties of these compounds are reported. All‐small‐molecule OSCs based on RC19 :TOCR1 and RC20 :TOCR1 active layers show power conversion efficiencies (PCEs) of 13.72% and 5.20%, respectively. It should be noted that the PCE of 13.72% obtained for RC19 :TOCR1 devices is, to one's knowledge, the highest value reported for porphyrin‐based binary OSCs. The higher PCE obtained for RC19 is due to its higher photon harvesting ability, more efficient exciton dissociation and charge transfer, balanced charge transport, and lower bimolecular and trap‐assisted recombination.