Designing Self-Assembled Dye–Redox Shuttle Systems via Interfacial π-Stacking in Dye-Sensitized Solar Cells for Enhanced Low Light Power Conversion

Productive electron transfer in dye-sensitized solar cells is critically important to achieving high-performing solar cell devices. In this regard, increasing the electron transfer rate between the dye and redox shuttle by noncovalent self-assembly of the dye and redox shuttle via π-stacking interactions is considered. In this study, a dye with a pyrene-based donor group (SS1) was synthesized and tested with two terpyridine-based redox shuttles. The [Co(tpypyr)2]3+/2+ redox shuttle (RS) has a pyrene substitution that allows for stronger π-stacking via pyrene–pyrene interactions than a benchmark unsubstituted terpyridine-ligated redox shuttle ([Co(tpy)2]3+/2+). DSC devices were fabricated with the dye and each redox shuttle, and the performances were evaluated by using current density–voltage (J–V), incident photon-to-current conversion efficiency (IPCE), small modulated photovoltage transient (SMPVT), photocurrent dynamic, and transient absorption measurements. Results show that pyrene groups on both the dye and RS increase the rate of dye regeneration and slow the recombination rate. A 22.8% power conversion efficiency (versus 12.4% for the system with no pyrene on the redox shuttle) under fluorescent lighting conditions is observed.