TiO۲ Blocking Under-layer in Nanostructured Solar Cells

چکیده مقاله

Electron recombination of photo-injected electrons with the oxidized form of mediator or with the hole-transporting medium is one of the main loss factors in nanostructured solar cells. It occurs both at the TiO2 surface and at the naked transparent conductive oxide coated glass areas, which are uncovered by the TiO2 nanoparticles. TiO2 sub-nanometer blocking under-layers are known to block the electron recombination, thus leading to an enhancement in the open-circuit potential and the efficiency of the solar cell. The recombination current over the transparent conductive oxide coated glass is relatively small in a liquid-type dye-sensitized solar cells but it becomes crucial in the solid state dye-sensitized solar cells. The blocking under-layer of TiO2 must be deposited on top of the transparent conductive oxide coated glass to prevent shunting of electrons from the transparent conductive oxide coated glass support to the hole-transporter. The blocking under-layer of TiO2 was deposited using spin-coating method. Different thicknesses of TiO2 were prepared to have different coverages. The layers were annealed at 450oC for 30 min. The results from XRD showed that the under-layer is in anatase phase. According to the SEM images, annealing at 450oC causes that the TiO2 nanoparticles aggregates on the transparent conductive oxide coated glasses, thereby the quality of TiO2 under-layer improved since the pinhole areas decrease. In addition, the increase numbers of deposition using spin-coating method decreased the electron recombination due to the decrease of the pinhole area