Improved performance of dye sensitized solar cell via fine tuning of ultra-thin compact TiO2 layer

Abstract

The role of properties of ultra-thin TiO2 compact layers (c-TiO2) deposited on fluorine-doped tin oxide (FTO) substrates, as a function of their thickness, has been studied by using electrochemical and optical techniques as well as surface morphology. The performance of films of thicknesses varying from 7nm to 20nm was compared with TiO2 films having a constant thickness (7nm) prepared with different precursor concentrations. The surface morphology of the compact layer was investigated using field emission scanning electron microscope (FESEM) and it was observed that a film thickness less than 10nm was sufficient to serve as a compact layer in the fabrication of dye sensitized solar cells (DSSCs). The power conversion efficiency (ɳ) of devices was found to be similar for a compact layer of thickness of 10nm and observed to degrade for thicknesses >10nm. This was attributed to the combined effect of optical transmittance, morphology, conductivity and position of Fermi level. Further, for devices prepared with compact layer of constant thickness (7nm), a significant improvement in the ɳ (5.2%) is obtained for DSSCs prepared using 10mM precursor concentration. The improvement in the ɳ is attributed to the facile transport as well as proper position of Fermi level without compromising optical and morphological properties. The analyses suggest that properties of the thin TiO2 compact layer play a significant role in the photovoltaic properties of DSSCs.