Effect of π-spacer rigidification on the optoelectronic properties and photovoltaic performance of small D-π-A molecules

This study investigates the impact of π-spacer rigidification on the optoelectronic and photovoltaic properties of small donor-π-acceptor (D-π-A) hydrazone-based molecules. Two new derivatives incorporating cyclopentadithiophene (CPDT) and dithienopyrrole (DTP) as rigid π-spacers were synthesized and characterized. Optical and electrochemical analyses reveal a red-shifted absorption profile and altered HOMO-LUMO energy levels compared to the reference molecule containing a non-fused bithiophene spacer. Despite enhanced light absorption, bilayer heterojunction solar cells based on these compounds exhibit lower power conversion efficiencies most probably because of the reduced short-circuit current density and fill factor. These results underscore the complex interplay between molecular design, charge transport, and device performance, providing valuable insights for the development of high-efficiency organic photovoltaic materials.