J-Aggregated Dyes for Dye-Sensitized Solar Cells: Suppressing Aggregation-Induced Excited-State Quenching by Intramolecular Charge Separation

Understanding and regulating the aggregation of organic photovoltaic materials have become the forefront of research in the study of organic solar cells. The aggregation-induced excited-state quenching (AIESQ) effect of sensitizers inevitably debilitates the charge separation and transportation, countering the dye-sensitized solar cell (DSSC) performance. In this study, we modified the donor moieties of prototype dye molecules constructed with a styryltriphenylamine donor and pyrimidine acceptor, endowing them with a strong tendency to form J-aggregates. The photophysical process analysis of the four designed dyes TPA-Pyc, TE-Pyc, ETE-Pyc, and TEBT-Pyc indicates their ability to form charge-separated states through photoinduced electron transfer (PET). Photovoltaic characterizations have revealed the positive aggregation effect on DSSC device performances. The addition of chenodeoxycholic acid (CDCA) inhibited dye aggregation and accounted for the decreased Jsc, Voc, and efficiency compared to without CDCA. Furthermore, electrochemical impedance spectroscopy (EIS) results demonstrate that the aggregation of dyes with charge-separated state characteristics helps suppress charge recombination without interfering with electron injection. This study offers insights for developing organic photovoltaic materials and paves the way to utilize the advantages of dye aggregation to advance DSSCs.