context: The photovoltaic performances of the crosslinked cells are higher than the non-crosslinked ones for both TiO2 and NiO based DSSCs, whatever the redox mediator used in the electrolyte. For TiO2 based DSSCs, this mostly results from a larger short circuit photocurrent density (Jsc) with the crosslinked dyes. On the other hand, the crosslinked NiO based p-DSSCs display much higher Voc with both redox mediators. However, on NiO based p-DSSCs the iodine based electrolyte gives lower Jsc after crosslinking. Jsc is controlled by the light harvesting efficiency (LHE), the charge injection quantum yield, the charge recombination reactions and by the charge collection efficiency. LHE is certainly not the cause of the lower Jsc, because the absorbance has not changed after crosslinking. Likewise, the hole injection efficiency is most certainly not affected by the crosslinking, because the current density is not diminished after crosslinking with the cobalt electrolyte. If an enhancement of the charge recombination reactions was the cause of the lower Jsc, first the Voc would be decreased as well, which is the reverse and second it would occur with the cobalt electrolyte, which is not the case either. Logically, we can therefore interpret the lower Jsc as a consequence of the lower efficiency of the dye regeneration step, which directly reduces the charge collection efficiency. It was previously reported by Xu and co-workers, that electron deficient triazoles similar to those involved in this study can make anion–π interaction with iodide. This hypothesis is supported by observing that the 1H NMR chemical shift of triazole of the reference compound benzyl-1,2,3-triazole-4-carboxylic acid methyl ester 15 was down-field shifted upon addition of Bu4NI in the NMR tube (Fig. S24†). As a result, after crosslinking the concentration of iodide is certainly raised in the vicinity of the DPP 2 and might therefore hinder the approach of triiodide and consequently limit the charge regeneration efficiency of the reduced DPP after hole injection. In both devices, the increase of the Voc after crosslinking is most probably due to lower interfacial charge recombination coming from lower access of the redox mediator to the surface semiconductor. Indeed, inspection of the current/voltage characteristics of the solar cell recorded in the dark demonstrate that current of the crosslinked solar cells is significantly lower than the non-crosslinked ones (Fig. S20–S23†). Interfacial charge recombination between the redox mediator and the hole in NiO is known to be a major source of energy loss in p-DSSCs, therefore it is not unexpected that the reduction of this process impacts more importantly NiO based solar cells than TiO2 DSSCs.
answer: iodine 