Blocking layer optimisation of poly(3-hexylthiopene) based Solid State Dye Sensitized Solar Cells

Abstract The optimisation study of the fabrication of a compact TiO 2 blocking layer (via Spray Pyrolysis Deposition) for poly(3-hexylthiopene) (P3HT) for Solid State Dye Sensitized Solar Cells (SDSCs) is reported. We used a novel spray TiO 2 precursor solution composition obtained by adding acetylacetone to a conventional formulation (Diisopropoxytitanium bis(acetylacetonate) in ethanol). By Scanning Electron Microscopy a TiO 2 layer with compact morphology and thickness of around 100 nm is shown. Through a Tafel plot analysis an enhancement of the device diode-like behaviour induced by the acetylacetone blocking layer respect to the conventional one is observed. Significantly, the device fabricated with the acetylacetone blocking layer shows an overall increment of the cell performance with respect to the cell with the conventional one (Δ J sc / J sc  = +13.8%, ΔFF/FF = +39.7%, ΔPCE/PCE = +55.6%). A conversion efficiency optimum is found for 15 successive spray cycles where the diode-like behaviour of the acetylacetone blocking layer is more effective. Over three batches of cells (fabricated with P3HT and dye D35) an average conversion efficiency value of 3.9% (under a class A sun simulator with 1 sun A.M. 1.5 illumination conditions) was measured. From the best cell we fabricated a conversion efficiency value of 4.5% was extracted. This represents a significant increment with respect to previously reported values for P3HT/dye D35 based SDSCs.