CdS quantum dots synthesized using sonochemical successive ionic layer adsorption

Fossil fuel resource exhaustion is an inescapable reality that is beginning to dawn on the human race. Currently, majority of the works largest economies are fossil fuel powered. Fossil fuels have the characteristic of increasing the amount of carbon in the atmosphere consequently causing global warming and climate change. Sooner than later, an overhaul of fossil fueled systems will be required. Among the many alternatives available, solar energy is most auspicious credit to the fact that its abundant. Recent developments have facilitated harvesting of solar energy through the introduction of low-cost high-efficiency solar cells, which are based on the structure of dye-sensitized solar cells.

Recently, quantum dots-sensitized solar cells (QDSCs) have been reported. QDSCs have a low production cost, excellent optoelectronic properties and potential to achieve high efficiency. In addition, the QDs fabricated solar cells have been theoretically known to be able to overcome the Shockley–Queisser limit, where photons with energies smaller than the band gap energy are not absorbed, whereas photons with energies larger than the band gap energy unnecessarily lose an excessive energy through thermalization.

Therefore, improved solar cell technologies using QDs are required, in order to achieve efficiencies higher than those of first generation photovoltaic cells. In this view, a group of researchers from the Kyungpook National University: Dr. Jae Ho Kim, Taehun Jang, Sae Rom Seo and Professor Sang Ho Sohn synthesized QDs that exhibit light absorption in most of the visible (VIS) light region, that could be used for the development of QDSCs. The researchers focused on the synthesis of CdS QDs as a light harvesting and charge generation layer and mesoporous TiO₂ (mp-TiO₂) nanoparticles as a charge transport layer by applying ultrasonic energy in the conventional successive ionic layer adsorption and reaction (SILAR) method, in a bid to increase the efficiency of CdS QDSCs. Their work is currently published in Journal of Physics and Chemistry of Solids.

The researchers started by fabricating CdS QDs/mp-TiO₂ photoanodes by introducing sonochemical energy in the conventional SILAR (SC-SILAR) method to improve their characteristics. They then applied Sonochemical energy of 300 W using sonochemical equipment when the mp-TiO₂ electrode was immersed in Cd and S precursors. Altogether, the characteristics of the CdS QDs fabricated with and without an application of sonochemical energy were analyzed following which the optimal synthesis conditions were investigated by changing.

The authors noted that the SC-SILAR method provided a shorter synthesis time and larger adsorption of the fabricated CdS QDs, compared with the conventional SILAR method. In addition, they highlighted that an optimal amount of sonochemical energy was observed by analyzing CdS QDs synthesized with different intensities of ultrasonic waves.

In summary, the used ultrasonic waves in the SILAR process to improve the synthesis efficiency of CdS QDs and mp-TiO₂ NP layer. Further, the sonochemical cavitation effects on the synthesis of CdS QDs were investigated. In an interview with Advances in Engineering, Professor Sang Ho Sohn, the lead author highlighted that the improved SC-SILAR method provided a shorter synthesis time and improved QD formation efficiency. Overall, experimental results confirmed that the SC-SILAR method was effective for the synthesis of QDs.