p-Type dye-sensitized solar cells based on pseudorotaxane mediated charge-transfer

The efficiency of p-type dye-sensitized solar cells (DSSCs) remains low compared to that of n-type congeners due to charge recombination events. We report a supramolecular approach to reduce recombination at the NiO–dye interface, realized by using the cyclophane cyclobis(paraquat-p-phenylene) ring (RING⁴⁺/RING^3˙+) as a redox mediator and a dye (P_N) functionalized with a 1,5-dioxynaphthalene (DNP) recognition site, promoting the supramolecular formation of a pseudorotaxane capable of directing charge transfer away from the NiO–dye interface. The binding affinity of RING⁴⁺ to P_N is high (K_ass = 3.4 × 10⁴ M⁻¹), with quenching of the photoexcited dye (P_N*) ascribed to reduction of RING⁴⁺ to RING^3˙+. The reduced RING^3˙+ exhibits a lower binding affinity to P_N, facilitating exchange with the excess RING⁴⁺ present in solution. This supramolecular phenomenon was implemented into p-type DSSCs by anchoring the P_N dye on a NiO photocathode in conjunction with the RING⁴⁺/RING^3˙+ redox couple, yielding a 10 fold enhancement in the short-circuit photocurrent (J_SC) compared to control devices utilizing P1 dye or the methylviologen (MV²⁺/MV^˙+) redox couple that cannot form pseudorotaxanes.