Co-sensitization of 3D bulky phenothiazine-cored photosensitizers with planar squaraine dyes for efficient dye-sensitized solar cells

A series of new phenothiazine-cored 3D bulky organic sensitizers TP1-TP4 have been prepared and employed in dye-sensitized solar cells (DSSCs). The 3D bulky configuration of these molecules can effectively retard the charge recombination at the TiO₂/electrolyte interface. Amongst the four dyes, the co-adsorbent-free DSSC based on the dye TP3 exhibited the best conversion efficiency (η) of 8.00%. Subsequently, the photosensitizer TP3 with strong UV-visible absorption and excellent performance in adsorbent-free DSSCs was co-sensitized with a near-infrared (NIR) absorbing squaraine dye YR6 to realize a UV-visible-NIR light-harvesting capability, which can effectively suppress the dye aggregation of YR6 with a planar structure and retard the charge recombination in the as prepared DSSC. Upon optimization, the co-sensitized DSSCs exhibited remarkable overall efficiency enhancements of 33% and 356% as compared with the devices based on TP3 and YR6 alone, respectively, and a high efficiency up to 9.84% was achieved at the TP3/YR6 molar ratio of 25 : 1.