Effect of Position of Donor Units and Alkyl Groups on Dye-Sensitized Solar Cell Device Performance: Indoline-Aniline Donor-Based Visible Light Active Unsymmetrical Squaraine Dyes.

Indoline (In) and aniline (An) donor-based visible light active unsymmetrical squaraine (SQ) dyes were synthesized for dye-sensitized solar cells (DSSCs), where the position of An and In units was changed with respect to the anchoring group (carboxylic acid) to have In-SQ-An-CO 2 H and An-SQ-In-CO 2 H sensitizers, AS1-AS5 . Linear or branched alkyl groups were functionalized with the N atom of either In or An units to control the aggregation of the dyes on TiO 2 . AS1-AS5 exhibit an isomeric π-framework where the squaric acid unit is placed in the middle, where AS2 and AS5 dyes possess the anchoring group connected with the An donor, and AS1 , AS3 , and AS4 dyes having the anchoring group connected with the In donor. Hence, the conjugation between the middle squaric acid acceptor unit and the anchoring -CO 2 H group is short for AS2 , AS5 , and AK2 and longer for AS1 , AS3 , and AS4 dyes. AS dyes showed absorption between 501 and 535 nm with extinction coefficients of 1.46-1.61 × 10 5 M -1 cm -1 . Further, the isomeric π-framework of An-SQ-In-CO 2 H and In-SQ-An-CO 2 H exhibited by means of changing the position of In and An units a bathochromic shift in the absorption properties of AS2 and AS5 compared to the AS1 , AS3 , and AS4 dyes. The DSSC device fabricated with the dyes contains short acceptor-anchoring group distance ( AS2 and AS5 ) showed high photovoltaic performances compared to the dyes having longer distance ( AS1 , AS3 , and AS4 ) with the iodolyte (I - /I 3 - ) electrolyte. DSSC device efficiencies of 5.49, 6.34, 6.16, and 5.57% have been achieved for AS1 , AS2 , AS3 , and AS4 dyes, respectively; without chenodeoxycholic acid (CDCA), small changes have been observed in the device performance of the AS dyes with CDCA. Significant changes have been noted in the DSSC parameters (open-circuit voltage V OC , short-circuit current J SC , fill factor ff, and efficiency η) for the AS5 dye while sensitized with CDCA and showed highest DSSC efficiency of 8.01% in the AS dye series. This study revealed the potential of shorter SQ acceptor-anchoring group distance over the longer one and the importance of alkyl groups on the overall DSSC device performance for the unsymmetrical squaraine dyes.