// New analytics for a better understanding of solar cells

With the relocation into the new building, new high-performance equipment was also installed at the analytical laboratory of the photovoltaic researchers. The equipment provides targeted support for the process development of thin-film solar cells. This applies in particular to new topics such as kesterite and perovskite solar cells, cadmium-free buffer layers and the spatial distribution of alkali elements, for example following PDT (post-deposition treatment).

One highlight is the new ToF.SIMS5 (ToF = time of flight; SIMS =
secondary ion mass spectrometry) system from IONTOF. Compared to the standard SIMS, ToF.SIMS gains a spatial component by scanning the sample (lateral resolution up to 100 nm) and recording one mass spectrum per pixel via measuring pulses. The sample can be measured with different ion sources in such a way that an optimal result can be achieved depending on the respective scientific question. For example, localising and quantifying alkali elements such as sodium, potassium, rubidium and caesium in the CIGS layer has been a topic of research for a long time, as these elements have a significant impact on the solar cell performance despite their small quantities. With ToF.SIMS, a method is finally available at ZSW with which the spatial distribution of these elements in the CIGS layer can be resolved. This means that it is possible to measure and quantify the concentration of alkali elements in the grain, at the grain boundary and at the interfaces between the layers. This information makes an important contribution to process definition, especially with regard to the transfer of processes from one system to another. The new method provides important key data for high-efficiency processes developed at the cell level to be realised at the module level.