Rotaxane-Functionalized Dyes for Charge-Rectification in p-Type Photoelectrochemical Devices

A supramolecular photovoltaic strategy is applied to enhance power conversion efficiencies (PCE) of photoelectrochemical devices by suppressing electron–hole recombination after photoinduced electron transfer (PET). Here, the author exploit supramolecular localization of the redox mediator—in close proximity to the dye—through a rotaxane topology, reducing electron–hole recombination in p-type dye-sensitized solar cells (p-DSSCs). Dye P _Rotaxane features 1,5-dioxynaphthalene recognition sites (DNP-arms) with a mechanically-interlocked macrocyclic redox mediator naphthalene diimide macrocycle (3-NDI-ring), stoppering synthetically via click chemistry. The control molecule P _Stopper has stoppered DNP-arms, preventing rotaxane formation with the 3-NDI-ring. Transient absorption and time-resolved fluorescence spectroscopy studies show ultrafast (211 ± 7 fs and 2.92 ± 0.05 ps) PET from the dye-moiety of P _Rotaxane to its mechanically interlocked 3-NDI-ring-acceptor, slowing down the electron–hole recombination on NiO surfaces compared to the analogue. p-DSSCs employing P _Rotaxane (PCE = 0.07%) demonstrate a 30% PCE increase compared to P _Stopper (PCE = 0.05%) devices, combining enhancements in both open-circuit voltages (V _OC = 0.43 vs 0.36 V) and short-circuit photocurrent density (J _SC = −0.39 vs −0.34 mA cm ⁻²). Electrochemical impedance spectroscopy shows that P _Rotaxane devices exhibit hole lifetimes (τ _h) approaching 1 s, a 16-fold improvement compared to traditional I ⁻/I ₃ ⁻-based systems (τ _h = 50 ms), demonstrating the benefits obtained upon nanoengineering of interfacial dye-regeneration at the photocathode.