New materials allow new technologies to convert sunlight into electricity and fuels. The combination of molecules and small nanoparticles makes these materials a reality. Molecules of these materials absorb sunlight very well and donate electrons to nanoparticles. The nanoparticles (Life cycle decoding of photogenerated charges) then move the electrons and catalyze the fuel-producing reactions. However, this process does not always work as researchers expect.
Now scientists have found a way to track electrons (Life cycle decoding of photogenerated charges) in their orbiting molecules to form nanoparticles. Researchers can measure where electrons move easily and when, where, when, and why they are fixed. This information is essential when looking for better combinations for new materials.
A study published in The Journal of Physical Chemistry Letters shows a new experimental tool that can track electrons traveling between molecules and nanoparticles that convert sunlight into electricity or fuels. It turns out that a very common nanoparticulate material, zinc oxide, first retains electrons for a while. The material allows the movement of electrons only on the surface of the nanoparticle. As a result, it is likely that the charges could disappear or damage the nanoparticulate material. The charges must essentially travel continuously and directly to the nanoparticles. The ability to detect these barriers to electronic travel will help researchers design better materials for converting sunlight into other forms of energy.
To convert sunlight into electricity or fuel, the material must absorb light and direct light energy into electrons. Then the electrons must circulate to create a current or perform chemical reactions. One way to achieve both steps is to use molecules that are very good at capturing sunlight and attach them to substrates that are very good at moving electrons. Scientists have previously known that electrons can move in a zinc oxide material much faster than many other materials. However, electrodes made of zinc oxide do not behave like electrodes of other materials. What happened?
Using a technique called time-resolved X-ray photoelectron spectroscopy in Advanced Light Source, a user facility in the Department of Energy’s Office of Science (DOE), scientists will now be able to track the path of electrons from molecules to substrates and beyond. . . They found that electrons had long been bound between the molecules and the zinc oxide. When the electrons can finally jump, the material continues to push into the surface of the substrate. There, electrons are more easily trapped than if they could travel directly across most of the substrate. This study helps explain why zinc oxide substrates did not behave as expected. It also provides a new test design for future materials.
