Annealing effect on Sb2S3-TiO2 nanostructures for solar cell applications

Abstract

Nanostructures composited of vertical rutile TiO2 nanorod arrays and Sb2S3 nanoparticles were prepared on an F:SnO2 conductive glass by hydrothermal method and successive ionic layer adsorption and reaction method at low temperature. Sb2S3-sensitized TiO2 nanorod solar cells were assembled using the Sb2S3-TiO2 nanostructure as the photoanode and a polysulfide solution as an electrolyte. Annealing effects on the optical and photovoltaic properties of Sb2S3-TiO2 nanostructure were studied systematically. As the annealing temperatures increased, a regular red shift of the bandgap of Sb2S3 nanoparticles was observed, where the bandgap decreased from 2.25 to 1.73 eV. At the same time, the photovoltaic conversion efficiency for the nanostructured solar cells increased from 0.46% up to 1.47% as a consequence of the annealing effect. This improvement can be explained by considering the changes in the morphology, the crystalline quality, and the optical properties caused by the annealing treatment.

Figure 1

Schematic of (a) bare TiO₂ nanorod arrays on FTO and (b) Sb₂S₃-TiO₂ nanostructure on FTO.

Figure 2

Typical top-view SEM images of TiO₂ nanorod arrays and Sb₂S₃-TiO₂ nanostructures. (a) SEM image of a TiO₂ nanorod array grown on SnO₂:F substrate by hydrothermal process. Inset: A low-magnification SEM image of the same sample. (b) SEM image of the as-grown Sb₂S₃-TiO₂ nanostructures. (c) SEM image of Sb₂S₃-TiO₂ nanostructures annealed at 300°C for 30 min.

Figure 3

XRD patterns. The bare TiO₂ nanorod arrays (a), the as-grown Sb₂S₃-TiO₂ nanostructure electrode (b), and the annealed Sb₂S₃-TiO₂ nanostructure electrode under 300°C (c).

Figure 4

Optical absorption spectra of Sb₂S₃-TiO₂ nanostructure samples. Before (green spectrum) and after being annealed at 100°C (red spectrum), 200°C (blue-green spectrum), 300°C (black spectrum), and 400°C (brown spectrum).

Figure 5

I-V curves for the solar cells assembled using Sb₂S₃-TiO₂ nanostructures annealed under varied temperature.