Abstract
In this present work, we report the deposition of cadmium selenide (CdSe) particles on titanium dioxide (TiO2) nanotube thin films, using the chemical bath deposition (CBD) method at low deposition temperatures ranging from 20 to 60 °C. The deposition temperature had an influence on the overall CdSe–TiO2 nanotube thin film morphologies, chemical composition, phase transition, and optical properties, which, in turn, influenced the photoelectrochemical performance of the samples that were investigated. All samples showed the presence of CdSe particles in the TiO2 nanotube thin film lattice structures with the cubic phase CdSe compound. The amount of CdSe loading on the TiO2 nanotube thin films were increased and tended to form agglomerates as a function of deposition temperature. Interestingly, a significant enhancement in photocurrent density was observed for the CdSe–TiO2 nanotube thin films deposited at 20 °C with a photocurrent density of 1.70 mA cm−2, which was 17% higher than the bare TiO2 nanotube thin films. This sample showed a clear surface morphology without any clogged nanotubes, leading to better ion diffusion, and, thus, an enhanced photocurrent density. Despite having the least CdSe loading on the TiO2 nanotube thin films, the CdSe–TiO2 nanotube thin films deposited at 20 °C showed the highest photocurrent density, which confirmed that a small amount of CdSe is enough to enhance the photoelectrochemical performance of the sample.
Highlights
The highly ordered TiO2 nanotube thin films were successfully synthesized in our previous report, with an average inner-tube diameter and tube length of 76 nm and 5.6 μm, respectively [21,47]
A clear surface morphology change was observed for all samples as function to the chemical bath temperature
A low chemical bath temperature of 20 ◦ C led to a low deposition rate, slowing the nuclei growth on the TiO2 nanotube thin films
Summary
Nanostructured titanium dioxide (TiO2 ) has been known as one of the most promising semiconductor materials, as it has been widely used in many applications, such as photocatalysts [1,2,3,4], photovoltaics [5,6,7,8,9,10,11], photoelectrochemical cells [12,13,14,15], supercapacitors [16,17,18,19], and sensors [20], Materials 2020, 13, 2533; doi:10.3390/ma13112533 www.mdpi.com/journal/materialsMaterials 2020, 13, 2533 due to its remarkable chemical, optical, and physical properties, as well as its low production cost and lower toxicity. The electrochemical anodization method has come to light, as it is proven to be the most facile and versatile method to synthesized TiO2 nanotube thin films due to its ability to modify the morphology, diameter, and length of the nanotubes by varying the anodization parameters. Their unique nanoarchitecture minimizes the photo-induced charge of the recombination loss of the carrier at the nanostructure connections, maximizing photon absorption [21,22]. The deposition of small band gap semiconductor materials as a sensitizer on the
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