Tungsten trioxide nanostructured electrodes for organic dye sensitised solar cells

Abstract

Tungsten trioxide (WO 3 ) nanospheres with diameter ranging from 10 nm to 500 nm were synthesised by a facile thermal oxidation process. By resistively heating metallic tungsten in oxygen atmosphere, WO 3 nanoparticles were produced in high yield. Optical, compositional, morphological and structural studies were performed by UV-VIS-NIR spectrophotometry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies. XPS studies revealed the formation of tungsten trioxide with oxygen deficiency. Analysis of the particle size (diameter) distribution of the as-deposited samples obtained from SEM micrograph exhibited a Gaussian-type distribution centred around 178 nm and characterised by a half width of 98.3 nm. As deduced from XRD analysis, the as-prepared tungsten trioxide (WO 3 ) nanoparticles were polycrystalline in nature and crystallised in the monoclinic phase. Electrophoretic deposition (EPD) was applied in coating the synthesised tungsten oxide nanoparticles onto fluorine doped tin oxide (FTO) coated quartz substrates for the fabrication of dye-sensitised solar cells (DSSC), with henna ( Lawsonia inermis ) as the natural organic dye. Nanoparticle suspension in double distilled water was used in the EPD process with an optimal electric field of 20 Vcm –1 at a current density of 1 mA/cm 2 . DSSCs developed using these films were tested through the measurement of their current density–voltage (J–V) and spectral photocurrent characteristics. A maximum IPCE of about 32% was obtained at around 450 nm.