From deposition to analysis – all at EMIL
Let´s come back to the perovskite. As mentioned before, the perovskite thin film in Nuria’s work is Pb-free. Therefore, she uses SnCl2 in addition to a CH3NH3I3 precursor (Methylammonium Iodide or shortly MAI). These are the precursors that are deposited during the evaporation phase explained above. Núria and I evaporated SnCl2 in of EMIL’s chambers, but MAI’s evaporation is executed outside of EMIL’s chambers since it is a very volatile compound that can cause contamination of the ultra-high vacuum system if something does not go as planned. Consecutively, I was not able to see the evaporation of the MAI. Nevertheless, once both precursors are deposited on the glass – they in principle should react to form the final perovskite thin film.
Claudia Hartmann and Marcus Bär giving Núria a hand.
And now follows the next important step: The perovskite layer can now be characterized in an XPS analysis chamber, which is also part of EMIL’s fancy equipment. While we were sitting and waiting with Núria for the XPS measurement to be done, she explained to me the working principle of the XPS characterization, too: “It is really simple in fact” - she said. “An X-ray source shoots photons of a known energy directly on the sample which in turn excites so called photoelectrons with a certain kinetic energy.
Because the excitation energy is known, the binding energy of the photoelectrons can be determined from their kinetic energy. An electron analyzer is used to measure the counts of electrons and their kinetic energy. Eventually, a plot of the counted electrons as a function of the binding energy is obtained” – says Núria, pointing on the monitor to such a plot. Núria will continue to work on this: diligently analyze the characterization results, if all goes well she will be able to prove that she indeed prepared perovskite thin film layers for potential solar energy applications.