Indacenodithienothiophene-based A-D-D0.625pt′0.625pt-D-A-type small-molecule donors for all-small-molecule organic solar cells

Research on all-small-molecule organic solar cells (SM-OSCs) is growing due to the advantages of small-molecule donor materials. In this study, we synthesized and characterized two small-molecule donors of A-D-D & PRIME;-D-A type based on highly fused indacenodithiophene (IDTT), namely BDT-IDTT-ORH and BDT-C8IDTT-ORH. The different side chains of these two molecules, 4-hexylphenyl and n-octyl, led to different crystallinities in the film state. The two synthesized donors exhibited absorption in the long wavelength range of 400-700 nm due to effective & pi;-conjugation caused by their planar structures. Because their absorption bands are complementary to that of the Y6 non-fullerene acceptor, these molecules showed potential as small-molecule donors in donor:Y6 blend for SM-OSCs. In particular, the BDT-C8IDTT-ORH:Y6 blend exhibited the highest power conversion efficiency (PCE) of 6.33%. This higher PCE is due to a relatively higher JSC value for BDT-C8IDTT-ORH with linear n-octyl side chains, thanks to its tighter molecular packing compared to that of BDT-IDTT-ORH with 4-hexylphenyl side chains.