Effect of Different Numbers of −CH₂– Units on the Performance of Isoquinolinium Dyes

Three new dyes have been synthesized to investigate the influence of the distance between the electron acceptor and TiO2 surface on the performance of dye-sensitized solar cells (DSSCs). In these dyes, the isoquinolinium acceptor, with a -(CH2)nCOOH anchoring group, and a functionalized triphenylamine donor are separated by an oligothiophene bridge. The physical and electrochemical properties of the dyes were investigated systematically. The results prove that different numbers of -CH2- units between the isoquinolinium acceptor and the carboxyl anchoring group have a less pronounced effect on the physical and electrochemical properties of these dyes. However, when applied in DSSCs, a sharp decrease in the short-circuit current (Jsc) was observed with increasing numbers of -CH2- units. For example, the device containing the organic dye bearing three -CH2- units produced the lowest Jsc of 7.94 mA·cm(-2). In contrast, the device containing the dye bearing only one -CH2- unit exhibited the highest Jsc of 13.88 mA·cm(-2). The higher photocurrent obtained with the device incorporating the dye with one -CH2- unit resulted in a higher power conversion efficiency of 6.8%.