Researchers have worked for many years to develop technologies that will help us combat the climate change crisis. All of them share one goal: to find sustainable energy sources that will replace toxic fossil fuels. If we can develop the technology necessary to make them, "Photocatalysts", which drive an artificial process that reproduces photosynthesis (in that solar energy is converted into useful materials), are promising. We can look to crystalline materials such as strontium titanate, (SrTiO3) as "photocatalysts", in order to move in this direction.Other reasons SrTiO3 are attractive include its potential use in resistive switches, fuel cell components, and other applications. SrTiO3's versatility has prompted physicists and engineers to investigate its different properties. We need to know more about the properties of SrTiO3.SrTiO3 and other photocatalytic materials are often "doped" using chemicals such as niobium (Nb), which improves their electrical properties. Photocatalysts can be subject to "charge recombination", which reduces their efficiency. This is when mobile charge carriers in the material such as "electrons", and "holes" can react with light to destroy each other. Research has shown that crystal defects can affect charge recombination. How does Nb doping impact the material properties SrTiO3's? This is what Prof. Masashi Kato and his team of researchers from Nagoya Institute of Technology in Japan wanted to discover.The researchers examined the effect of Nb doping at low concentrations and no doping on surface recombination of SrTiO3 crystals in their study, published in Journal of Physics D. Applied Physics. Professor Kato explained, "Quantitatively measuring effects of surfaces and niobium impureties in SrTiO3 carrier recombination on photocatalysts can help us design photocatalysts that have an optimal structure for artificial photosynthesis."First, the scientists used a technique called "microwave-photoconductivity decay" to analyze surface recombination patterns, or "decay", of undoped SrTiO3 and doped samples. Another technique, called "time-resolved photosenescence", was used to further investigate the bulk carrier recombination characteristics of doped samples as well as the different energy levels introduced through Nb doping.Researchers found that excited carrier recombination was independent of their concentration. This suggests that they recombine via "surface" and "Shockley-Read-Hall processes, which are not sensitive to the exciting carrier concentration. The doped samples showed faster decay curves which may be due to Nb doping. The negative effects of carrier doping were seen when the material was doped with high levels of Nb. The size and shape of the photocatalyst had an impact on surface recombination as well as its overall efficiency.It was found that Nb-doped SrTiO3 can be more beneficial than pure SrTiO3, particularly when operating at higher temperatures. These results can be used to design SrTiO3 photoscalysts that have a lower surface recombination rate and higher energy conversion. This will allow us to develop efficient and sustainable energy sources.Prof. Kato concludes optimistically, "We are confident our findings can accelerate development of artificial photosynthesis technology, ultimately contributing to a greener and more sustainable society."
