Enhanced photoelectrochemical properties of TiO2 nanotube arrays sensitized with energy-band tunable (Cu2Sn)x/3Zn1−xS nanoparticles

• TNTs sensitized with (Cu2Sn)x/3Zn1−xS nanocrystals were prepared.
• The coupling systems present an enhanced photoelectrochemical response.
• Energy band alignments of TNTs and (Cu2Sn)x/3Zn1−xS were determined.
• Conduction band offsets (CBO) between them were estimated.
• Relationship between CBO and photocurrent enhancement was obtained.

In this paper, TiO2 nanotube (TNT) arrays and (Cu2Sn)x/3Zn1−xS (x = 0.75, 0.24, and 0.09) nanocrystals were prepared, and TiO2 nanotubes (TNTs) were sensitized with (Cu2Sn)x/3Zn1−xS nanocrystals. Compared with the plain TNTs, (Cu2Sn)x/3Zn1−xS sensitized TNTs present an enhanced photoelectrochemical response. The photocurrent enhancement was characterized with the photocurrent ratio of (Cu2Sn)x/3Zn1−xS sensitized TNTs to plain TNTs, which were 1.50, 1.63, and 2.13 for (Cu2Sn)x/3Zn1−xS with the composition of x = 0.75, 0.24, and 0.09, respectively. To understand this phenomenon, the energy band alignments of TNTs and (Cu2Sn)x/3Zn1−xS were investigated, based on which the conduction band offsets (CBO) between TNTs and (Cu2Sn)x/3Zn1−xS were determined, which were 0.31, 0.47, and 0.63 eV for (Cu2Sn)x/3Zn1−xS with the composition of x = 0.75, 0.24, and 0.09, respectively. These results display that the photocurrent enhancement becomes large with the increase of CBO, which indicates that the enhanced photoelectrochemical response is mainly due to the energy level matching between TNTs and (Cu2Sn)x/3Zn1−xS, and the variation of enhancement is resulting from the change of CBO.