Exploring the hidden secrets of materials using spectroscopy
Over 60% of Germans rely on glasses and unsurprisingly, this is not a modern phenomenon. The first eyeglasses were made in Italy in the 13th century and their importance has grown since.
But sometimes, good vision is not sufficient in order to explore the hidden secrets of materials. In the last century, physicists have developed a method called spectroscopy, which is a technique used to analyse light by breaking it up into its component colours and it’s something that I am doing very regularly during the summer student programme at the HZB.
Designing the next generation of solar cells means finding the optimum material that can make them cheaper, more efficient, safer or simply better. One technique that I am currently using is X-ray photoelectron spectroscopy (XPS). In XPS, a material is exposed to a beam of X-rays, which excites electrons from the core levels of the atoms and causes the ejection of photoelectrons. The number of photoelectrons escaping from the top part of the material and their kinetic energy is then measured. This enables us to deduce not only the chemical composition but also the chemical and electronic state of each element in the surface.
In my project, I am currently looking at p-type semiconductors that could be used as a hole transport material (HTM) in a tandem solar cell consisting of a CIGS bottom cell and a perovskite top cell. To fully characterise these HTM layers, I also need to use other spectroscopic techniques in order to find their optical properties or their energy bands. In the end, combining all this information should enable us to find the best option for a tandem solar cell and should provide me with enough work for the remaining five weeks.