PbS sensitized TiO2 nanotube arrays with different sizes and filling degrees for enhancing photoelectrochemical properties

Abstract

PbS nanoparticles (PbS NPs), an efficient sensitizer for TiO₂ nanotube arrays (TiO₂ NAs), were fabricated by the method of sonication-assisted successive ionic layer adsorption and reaction (SILAR). The filling degree and size of PbS NPs can be tuned by changing the repeated cycles (N) of the SILAR process. TiO₂ NAs can be fully covered with PbS NPs with a size ranging from less than 4 nm to 25 nm and large aggregates inside and outside the nanotubes when N reaches 15. The growth mechanism of PbS NPs in TiO₂ NAs was expounded in great detail in this work. Ultraviolet-visible diffuse-reflectance spectra and surface photovoltage spectroscopy were used to investigate the light absorption properties and the transfer behavior of photogenerated charges in PbS-modified TiO₂ NA heterostructures. Results show that the absorption range of TiO₂ NAs is extended from the ultraviolet to the visible region by PbS NPs modification. A heterojunction is formed between PbS NPs and TiO₂ NAs, facilitating the separation of photogenerated charge carriers. This PbS NPs fully-covered TiO₂ NA electrode exhibits the best photoelectrochemical performance in all PbS-sensitized TiO₂ NA electrodes, due to a larger number of small PbS NPs (<4 nm). With AM 1.5G illumination at 100 mW cm⁻², its short-circuit current density, open-circuit voltage and photoelectric conversion efficiency are 9.55 mA cm⁻², 0.95 V and 2.83%, respectively.