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.