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⁻/I₃⁻-based systems (τ_h = 50 ms), demonstrating the benefits obtained upon nanoengineering of interfacial dye-regeneration at the photocathode.