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-COH and An-SQ-In-COH sensitizers, . 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. exhibit an isomeric π-framework where the squaric acid unit is placed in the middle, where and dyes possess the anchoring group connected with the An donor, and , , and dyes having the anchoring group connected with the In donor. Hence, the conjugation between the middle squaric acid acceptor unit and the anchoring -COH group is short for , , and and longer for , , and dyes. dyes showed absorption between 501 and 535 nm with extinction coefficients of 1.46-1.61 × 10 M cm. Further, the isomeric π-framework of An-SQ-In-COH and In-SQ-An-COH exhibited by means of changing the position of In and An units a bathochromic shift in the absorption properties of and compared to the , , and dyes. The DSSC device fabricated with the dyes contains short acceptor-anchoring group distance ( and ) showed high photovoltaic performances compared to the dyes having longer distance (, , and ) with the iodolyte (I/I) electrolyte. DSSC device efficiencies of 5.49, 6.34, 6.16, and 5.57% have been achieved for , , , and dyes, respectively; without chenodeoxycholic acid (CDCA), small changes have been observed in the device performance of the dyes with CDCA. Significant changes have been noted in the DSSC parameters (open-circuit voltage , short-circuit current , fill factor ff, and efficiency η) for the dye while sensitized with CDCA and showed highest DSSC efficiency of 8.01% in the 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.