Photoelectrochemical performance of cadmium sulfide quantum dots modified titania nanotube arrays

• CdS QDs are uniformly loaded into short and long TiO2 NTAs to form CdS QDs/TiO2 NTAs.
• The correlation between TiO2 NTAs and CdS QDs is disclosed for CdS QDs/TiO2 NTAs.
• Nanotube length of TiO2 NTAs predominantly affects photocurrent of CdS QDs/TiO2 NTAs.

The cadmium sulfide quantum dots modified titania nanotube arrays (CdS QDs/TiO2 NTAs) were prepared through a sequential sonication-assisted chemical bath deposition (CBD) process. The morphology and microstructure of CdS QDs/TiO2 NTAs were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy and UV–vis diffuse reflectance spectroscopy. The photoelectrochemical performance of CdS QDs/TiO2 NTAs was investigated under solar light illumination. The affecting parameters were studied including the nanotube length of TiO2 NTAs, CBD cycles of CdS QDs and the annealing treatment of CdS QDs/TiO2 NTAs. CdS QDs synthesized through 8 CBD cycles could uniformly cover on the tube walls of TiO2 NTAs to form unique CdS QDs/TiO2 NTAs with an open pore mouth. The appropriate annealing treatment at 400 °C for 60 min in N2 atmosphere could improve the crystallinity of CdS QDs, and accordingly enhance the photovoltaic properties of CdS QDs/TiO2 NTAs. Significantly, the nanotube length was the predominant factor affecting photoelectrochemical performance of CdS QDs/TiO2 NTAs. The unannealed CdS QDs/TiO2 NTAs with an optimal nanotube length of 12 μm achieved a short-circuit photocurrent density of 4.37 mA cm− 2, an open circuit photovoltage of 1.10 V and a top photoconversion efficiency of 3.56%. Comparatively, the annealed CdS QDs/TiO2 NTAs with an optimal nanotube length of 4 μm achieved a short-circuit photocurrent density of 6.31 mA cm− 2, an open circuit photovoltage of 1.23 V and a top photoconversion efficiency of 4.18%. The suitable modification of crystalline CdS QDs could well improve the photoelectrochemical performance of TiO2 NTAs photoanode.