Charge-transfer dynamics at the interface between NiO and C60 with porphyrin dyes furnished with different anchoring groups in p-type dye-sensitized solar cells

Three novel porphyrins have been synthesised with varying anchoring groups, using ‘click’ methodology. Synthetic routes were developed to several azide-functionalised anchors, which were successfully linked to a chromophore via a CuAAC. The distinct spectroscopic properties of the porphyrins allowed a detailed investigation of the adsorption behaviour of various anchoring groups. All three dyes were tested in p-DSCs and performed relatively modestly, but these results were comparable or higher to other porphyrins tested in the literature, which do not contain a secondary electron acceptor. IPCE measurements confirmed that excitation of the porphyrin was contributing toward the photocurrent for each device.In an attempt to improve the solar cell performances, a supramolecular system was tested, where the porphyrin was coordinated to a pyridyl-functionalised fullerene (C₆₀PPy). This was intended to extend charge lifetimes and therefore increase the J_SC. p-DSCs made using porphyrin/C₆₀PPy had a lower PCE, mainly due to a lower V_OC, which has been attributed to an increase in recombination when the fullerene is present. It was speculated that this was due to the fullerene anchoring directly to NiO and introducing an alternative recombination pathway. Cheno was used to block the free surface sites prior to the coordination of C₆₀PPy, to try and block this anchoring. After dying with cheno, there was a reduction in the film absorptivity due to porphyrin displacement. However, devices made using porphyrin/cheno/C₆₀PPy slightly outperformed the porphyrin alone, which was due to an improved APCE. This has been tentatively attributed to an improvement in the charge collection efficiency, due to an increased charge lifetime when the fullerene is present.