Charge-separated sensitizers with enhanced intramolecular charge transfer for dye-sensitized solar cells: Insight from structure-performance relationship

A series of charge-separated (CS) sensitizers with various donor modules and pyrimidine as acceptor were synthesized and employed to explore the effect of donor structure engineering on the properties of CS sensitizers and photovoltaic performances of dye-sensitized solar cells (DSSCs). Using previously reported CS sensitizer MTPA-Pyc or YD-Pyc as the model molecule, cyano group or benzotriazole were incorporated into the donor module and the electrochemical, spectral and photophysical properties were investigated. Incorporating electron-withdrawing structures enhances the intramolecular charge transfer (ICT) and conjugation of the donor module which leads to not only remarkably red-shifted absorption spectra, but also elongated lifetime of CS state of the sensitizers, thus resulting in an over 30% increase of power conversion efficiency (PCE) of the DSSCs. Combination of an electron-withdrawing benzotriazole with a strong electron-donating indoline moiety in the donor module produces the best PCE of 7.41% for DSSC based on YDBT-Pyc. Our results provide not only the rational design principles for CS sensitizers, but also insight into the feasibility of CS sensitizers for high performance photovoltaic applications.