摘要
Major loss factors for photo-generated electrons due to the presence of surface defects in titanium dioxide(Ti O_2)were controlled by RF-sputtered tungsten trioxide(WO_3) passivation. X-ray photoelectron spectroscopy assured the coating of WO3 on the Ti O_2 nanoparticle layer by showing Ti 2 p, W 4 f and O 1 s characteristic peaks and were further confirmed by X-ray diffraction studies. The coating of WO_3 on the Ti O_2 nanoparticle layer did not affect dye adsorption significantly. Dye sensitized solar cells(DSSCs) fabricated using WO_3-coated Ti O_2 showed an enhancement of ~10% compared to DSSCs fabricated using pristine Ti O_2-based photo-electrodes. It is attributed to the WO_3 passivation on Ti O_2 that creates an energy barrier which favored photo-electron injection by tunneling but blocked reverse electron recombination pathways towards holes available in highest occupied molecular orbital of the dye molecules. It was further evidenced that there is an optimum thickness(duration of coating) of WO_3 to improve the DSSC performance and longer duration of WO_3 suppressed photo-electron injection from dye to Ti O_2 as inferred from the detrimental effect in short circuit current density values. RF-sputtering yields pinhole-free,highly uniform and conformal coating of WO_3 onto any area of interest, which can be considered for an effective surface passivation for nanostructured photovoltaic devices.
