Introducing 4-Methoxythiophene Side Chains into β-Functionalized Porphyrins to Enhance Their Photovoltaic Performance

Compared to the extensive studies on meso-substituted porphyrins for organic solar cells (OSCs), β-substituted porphyrins have received less attention. Recently, we developed β-functionalized porphyrins and achieved OSCs with a power conversion efficiency (PCE) of 6.96%, indicating that the functionalization at the β positions is promising for OSCs. Considering that side-chain engineering plays important roles in developing high-efficient photovoltaic materials and 4-methoxy-modified thiophene group is frequently employed as the side chains in polymer donors to enhance the photovoltaic performance, here in, we introduced 4-methoxythiophene with 2-ethylhexyl (EH) and 2-hexyldecyl (HD) at two of the meso positions, connected diketopyrrolopyrrole (DPP) units directly to four of the β positions of a porphyrin core, and synthesized two small molecular donors 4β-DPP-MOT(EH)-Por and 4β-DPP-MOT(HD)-Por, respectively. Compared with the porphyrins with alkyl side chains reported previously, the introduction of 4-methoxythiophene side chains improves the intermolecular interactions. Especially, 4β-DPP-MOT(EH)-Por:Y6 blend afforded a more favorable morphology, which facilitates efficient charge transport and inhibits charge recombination. Consequently, the 4β-DPP-MOT(EH)-Por:Y6-based OSCs exhibited a champion PCE of 9.18%, higher than that of the 4β-DPP-MOT(HD)-Por-based device (8.14%). These studies demonstrated the potentials of developing highly efficient small-molecule donor materials by side-chain engineering to optimize the morphology of the blend films.