Push–pull structured (D–π–A) Zn(II)–porphyrin sensitizers, containing various electron donor groups for the enhancement of the light-harvesting ability within the expanded absorption region and efficient prevention of undesirable charge recombination of the sensitising dyes in dye-sensitized solar cells (DSSCs) were newly designed and synthesised through molecular engineering.¹ We investigated the effect of bulky donor groups in the D-p-A structured porphyrins on retarded charge recombination between the electrolytes and TiO₂ surface and enhanced power-conversion efficiency (PCE). The photovoltaic (PV) performance of the SGT sensitizer-based DSSCs, employing cobalt redox couples, were systematically evaluated in a thorough comparison with SM315 as a reference sensitizer. By introducing a more bulky fluorene unit containing alkoxyphenyl unit to the amine donor group in the world champion SM315 porphyrin dye, for efficient prevention of undesirable charge recombination, the PCE was enhanced. As a consequence, we observed a maximum 12.05% PCE for SGT-021 under simulated one-sun illumination (AM1.5G, 100 mWcm^-2), whose PCE was much higher than the 11.67% PCE of SM315, which was known as the world champion dye with a world record PCE of 13%. To further improve the maximum efficiency of the DSSCs, the first parallel-connected (PC) tandem DSSCs employing cobalt electrolyte in the bottom cell with SGT-021 and the top cell with SGT-137² were demonstrated and an extremely high efficiency of 14.64% was found, which is currently the highest reported value for dye-sensitised tandem solar cells. In this presentation, Zn-Porphyrin sensitizers for superior performance dye-sensitized solar cells and their tandem solar cells will be described.

References

1. S. H. Kang and H. K. Kim, et.al., Adv. Energy Mater. 7(2017) 1602117.
2. Y. K. Eom and H. K. Kim, et.al., J. Mater. Chem. A, 5(2017) 2297.