Assembly, charge-transfer and solar cell performance with porphyrin-C 60 on NiO for p-type dye-sensitized solar cells

A series of zinc tetraphenylporphyrin photosensitizers furnished with three different anchoring groups, benzoic acid, phenylphosphonate and coumarin-3-carboxylic acid, were prepared using ‘click’ methodology. All three gave modest performances in liquid junction devices with I 3 – /I – as the electrolyte. The distinct spectroscopic properties of the porphyrins allowed a detailed investigation of the adsorption behaviour and kinetics for charge transfer at the NiO|porphyrin interface. The adsorption behaviour was modelled using the Langmuir isotherm model and the phosphonate anchoring group was found to have the highest affinity for NiO (6.65 × 10 4 M −1 ) and the fastest rate of adsorption (2.46 × 10 7 cm 2 mol −1 min −1 ). The photocurrent of the p-type dye-sensitized solar cells increased with increasing dye loading and corresponding light harvesting efficiency of the electrodes. Coordinating the zinc to a pyridyl-functionalized fullerene ( C 60 PPy ) extended the charge-separated state lifetime from ca 200 ps to 4 ns and a positive improvement in the absorbed photon to current conversion efficiency was observed. Finally, we confirmed the viability of electron transfer from the appended C 60 PPy to phenyl-C61-butyric acid methyl ester, a typical electron transporting layer in organic photovoltaics. This has implications for assembling efficient solid-state tandem solar cells in the future. This article is part of a discussion meeting issue ‘Energy materials for a low carbon future’.