Star-shaped small molecular donors based on a Zn-Porphyrin core and DPP arms via different linkers for organic solar cells

Star-shaped porphyrin-based small-molecule donors (SMDs) with all four-directional substitution have been rarely reported. Herein, we designed and synthesized two SMDs, namely ZnP-4PhDPP and ZnP-4ThDPP, by employing zinc porphyrin as the core, thiophene-capped diketopyrrolopyrrole (DPP) as the four conjugated arms via a phenyl or thienyl linking bridge. The varied linker resulted in differences in absorption, energy level and molecular geometry. Blended with Y6 as acceptor, all-small-molecule devices achieved power conversion efficiency (PCE) of 6.86% and 6.93% for ZnP-4PhDPP and ZnP-4ThDPP, upon different device post-treatment conditions, respectively. The more orthogonal spatial configuration of ZnP-4ThDPP was favorable for constructing additional charge pathways, which was in accord with the results from photoluminescence quenching efficiency, charge transport ability and thickness sensitivity evaluation. The results in this work enriched the category of star-shaped porphyrin-derivatives and might afford guidelines into the structure-property correlation of various linkers-based small-molecule photovoltaic materials.