title: Regioisomeric effects on the electronic features of indenothiophene-bridged D-π-A'-A DSSC sensitizers.
abstract: Two D-π-A'-A regioisomers (A-IDT-D and D-IDT-A) featuring 4,4'-di-p-tolyl-4 H-indeno[1,2-b]-thiophene as a π linker (π) between the diarylamino donor (D) and the pyrimidine-cyanoacrylic acid acceptor (A'-A) have been successfully synthesized and characterized as efficient sensitizers for the dye-sensitized solar cells (DSSCs). The different arrangements of the D and A'-A blocks on the unsymmetrical indenothiophene (IDT) core render the dipole of IDT being along (A-IDT-D) or opposite (D-IDT-A) to the direction of intramolecular (donor-to-acceptor) charge transfer, and thus induce variations in the physical properties. The experimental observations correlated well with the theoretical analyses, clearly revealing the trade-off between the molar extinction coefficient (ε) and the S0 →S1 transition energy. As a result, a superior ε value was observed for D-IDT-A, whereas a bathochromic shift in the absorption occurred in A-IDT-D. The larger ε value of D-IDT-A together with its more favorable energy level relative to TiO2 led to a higher power conversion efficiency of 7.41 % for the D-IDT-A-based DSSC, retaining approximately 95 % of the N719-based DSSC efficiency. This work manifests the clear structure-property relationship for the case of donor and acceptor components being connected by an unsymmetrical π linker and provides insights for molecular engineering of organic sensitizers.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei 10617 (Taiwan).
authors.forename: Shu-Hua
authors.initials: SH
authors.lastname: Chou
authors.forename: Chih-Hung
authors.initials: CH
authors.lastname: Tsai
authors.forename: Chung-Chih
authors.initials: CC
authors.lastname: Wu
authors.forename: Dhirendra
authors.initials: D
authors.lastname: Kumar
authors.forename: Ken-Tsung
authors.initials: KT
authors.lastname: Wong
keywords: donor-pi-acceptor-acceptor; dyes/pigments; indenothiophenes; intramolecular charge transfer; organic sensitizers; solar cells