Cyano-Borazine Photosensitizers for Dye-Sensitized Solar Cells

Implementing novel metal-free and strongly absorbing donor–acceptor sensitizers without carboxylic acid anchoring groups are still a frontier in dye-sensitized solar cells (DSSCs). Herein, the facile synthesis of a strongly absorbing sensitizer combining three 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) anchoring moieties with a borazine core instead of the classical cyano anchoring groups, such as tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE), and the dimethyl-phenyl amino donor group, is disclosed. This results in a 1.6-fold increase in solar energy conversion efficiency compared to DSSCs with the reference sensitizers (TCBD-dimethyl-amino-phenyl core) and the prior art cyano-sensitizers with TCNE and TCNG anchors. The advantages of the TCBD-borazine design are twofold: 1) threefold increase in absorption extinction coefficient as well as 2) a reduction in back electron transfer and aggregation behavior upon dye adsorption onto the semiconducting electrode, resulting in 45% and 23% improvement in open-circuit voltage (V_oc) and short-circuit current density (J_sc), respectively, compared to those of the prior art. Overall, this work highlights an easy-to-design of cyano-sensitizer that results in a significant improvement of solar energy conversion when using borazine frameworks for the first time.