Effect of structural engineering of π-spacers on anti-aggregation of D–A–π–A dyes
In this paper, the encapsulated insulated molecular wire (EIMW) and 2′,7′-bis(hexyloxy)spiro[cyclopenta[2,1-b:3,4-b′]dithiophene-4,9′-fluorene] (SPDF) were specifically designed as efficient anti-aggregation π-bridges for two novel D–A–π–A metal-free sensitizers (IBT1 and IBT2). Compared with the reference dye IBT3 with 3,3′-dihexyl-2,2′-bithiophene (DHBT) as an anti-aggregation π-bridge, both the dyes IBT1 with EIMW and IBT2 with SPDF as π-bridges can suppress intermolecular aggregation more efficiently. The π-bridge of SPDF shows the strongest anti-aggregation ability due to the rigid ‘T’ configuration among these dyes. Meanwhile, the π-bridge of EIMW shows better anti-aggregation ability than DHBT because of the larger steric hindrance of the former. Finally, when the dyes IBT1 and IBT2 are co-sensitized with IBT3, respectively, the new devices exhibit high efficiencies of 7.85% and 7.64%, respectively, which are comparable to that of N719 (7.85%). The results demonstrate that the dyes with EIMW and SPDF as anti-aggregation π-bridges are promising candidates for efficient DSSCs and dye aggregation can be effectively inhibited by structural engineering of the π-spacer.