TiO₂ sensitization with Bi₂S₃ quantum dots: The inconvenience of sodium ions in the deposition procedure

This paper highlights the inconvenience of sodium ions in the Bi ₂S₃ quantum dots (QDs) deposition procedure, on the TiO₂ surface, for the conversion efficiency of the sensitized solar cells derived from these materials. Porous TiO₂ electrodes were sensitized with QDs obtained by the successive ion layer adsorption and reaction (SILAR) technique, using aqueous solutions of Bi(NO₃)₃ as the cation precursor and Na₂S as the sulfide source. Independently, elemental sulfur vapor was used to replace the Na₂S solution in the synthesis procedure. The obtained layers were characterized by X-ray diffraction, transmission electron microscopy, Raman scattering, and diffuse reflectance spectroscopy. We found that the presence of sodium ions in the reaction system strongly affects the formation of Bi₂S₃ on the porous TiO₂. This result contrasts with what other authors have claimed. Using elemental sulfur vapor as a precursor, crystalline Bi ₂S₃ nanoparticles are formed on the TiO₂ surface. The sensitized solar cells produced using the two different types of photoelectrodes were compared based on the photocurrent-voltage characteristic and the photocurrent time stability. The sensitized photoelectrodes derived from elemental sulfur vapor are much more stable over time and can achieve an efficiency of 0.84%. This is the highest conversion efficiency value for any Bi₂S₃ photoelectrochemical cell.