Core effect on indacenodithieno[3,2-b]thiophene dimer based small molecule acceptors for non-fullerene polymer solar cells

Dimerization is a widely adopted approach to construct electron accepting materials for polymer solar cells (PSCs). Fullerene dimers were extensively explored with improved structural stability and perylene-diimide (PDI) dimers prevented the formation of undesired large crystals. However, dimers of indacenodithieno[3,2-b] thiophene (IDTT) chromophores have yet not been reported despite the great success in non-fullerene small molecule acceptors (NF-SMAs) such as ITIC. In this work, we designed and synthesized three IDTT dimers with conjugated cores or not and explored the core effect of introducing flexible dithiophene or rigid thienothiophene as linkage group. All the three IDTT dimers were found to be poorly crystallized and functional PSCs devices containing each of these dimers were successfully fabricated paring with donor polymer PBDB-T. The introduction of electron donating linkages raise energy levels of the dimers hence increased the open circuit voltages. Thienothiophene was found to be a more suitable linkage unit than dithiophene but the highest power conversion efficiency of 6.01% was recorded in devices based on dimer dIDTT without the linkage units. This work demonstrated the possibility of using IDTT chromophore to construct dimer NF-SMAs and revealed insights of core effect on their photovoltaic performance.

Automated summary

This work focused on the design and synthesis of three IDTT dimers for use in PSCs, exploring the impact of core effects on their performance. It was found that introducing electron-donating linkages raised energy levels of the dimers, leading to increased open-circuit voltages. Thienothiophene was identified as a more suitable linkage unit compared to dithiophene, with the highest power conversion efficiency recorded in devices based on dimer dIDTT.