Insights into the sensitization effect and microscopic essence of π-linker structure regulation of metal-free organic dyes on the photovoltaic performance of dye-sensitized solar cells

Abstract

Our work aims to understand and reveal the origin of sensitization differences among newly designed dye sensitizers with conjugated and non-fully conjugated π-linker structures, further ascertaining how to improve the power conversion efficiency of dye-sensitized solar cells (DSSCs) by regulating π-linkers. The processes of intramolecular electron excitation transfer, interfacial electron injection, dye regeneration and charge recombination are comprehensively investigated by density functional theory calculations in chloroform and acetonitrile to predict the photoelectric performance of the new dye sensitizers we designed. These dyes can help DSSCs achieve large open-circuit voltage and short-circuit current density, indicating their excellent photovoltaic performance. Although the designed non-fully conjugated linker is embedded, the selected excellent donor and acceptor can match it, allowing the dye sensitizer to reach acceptable sensitization effects on the TiO₂ electrode, which depends on the monodentate adsorption and a special mechanism of intramolecular electron excitation transfer. The designed dyes have the extremely desirable characteristic of capturing I₂ more efficiently in the regions of the donor and π-linker far away from the acceptor due to stronger halogen bonding and more binding sites, so as to suppress charge recombination and increase the injected electron lifetime. For dye–I₂ complexes, the shorter B⋯I bond, longer I–I bond and larger absolute values of the charge variations of B and I₂ result in a stronger halogen bond, where B represents each active binding site of the dyes. Calculation results can inspire the experimental synthesis and application of these novel dyes and provide theoretical guidance for further design and development of more efficient sensitizer materials.