Solar energy conversion by the regular array of TiO2 nanotubes anchored with ZnS/CdSSe/CdS quantum dots formed by sequential ionic bath deposition

Abstract

The photoelectrode fabricated with the regular array of TiO2 nanotubes anchored with ZnS/CdSSe/CdS quantum dots was prepared by the following steps: 1) the formation of the regular array of TiO2 nanotubes on Ti metal, 2) the surface treatment of the TiO2 nanotubes with TiCl4 for the removal of surface defect sites, 3) the sequential deposition of CdS, CdSSe, and ZnS, in situ, onto the channel walls of TiO2 nanotubes by the successive ionic layer adsorption and reaction (SILAR) procedure. The tuning the band gap of CdSSe was done in terms of controlling the composition of Cd, S, or Se during the SILAR procedure. In this way, a ladder-like energy structure suitable for carrier transfer was attained from ZnS/CdSSe/CdS through TiO2 nanotubes to a Ti metal sheet. The more photoinduced charge carriers were generated and transferred from the anchored quantum dots to the TiO2 nanotubes and thus, the solar energy conversion efficiency was enahnced. The power conversion efficiency (PCE) of our solar cell fabricated with the regular array of TiO2 nanotubes anchored with CdSSe/CdS or CdSe/CdS quantum dots was PCE = 3.49 % and 2.81 % under the illumination at 100 mW/cm2, respectively. To protect the photocorrosion of our solar cell photoanode from the electrolyte and to prevent the recombination, ZnS was introduced onto CdS/CdSSe. The power conversion efficiency (PCE) of our solar cell with the structure of a photoanode electrode, (ZnS/CdSSe/CdS/ TiO2 NTs/ a Ti metal sheet) was 4.67 % under the illumination at 100 mW/cm2.