Affiliation:
1. RWTH Aachen I. Physikalisches Institut IA Sommerfeldstraße 14 52074 Aachen Germany
2. Martin Luther-Universität Halle-Wittenberg Institut für Physik FG Photovoltaik 06099 Halle Germany
3. Albert-Ludwigs Universität Freiburg INATECH Emmy-Noether-Straße 2 79110 Freiburg Germany
Abstract
In this work, the dual effect of Na in the copper indium gallium diselenide (CIGS) absorber is studied. Na doping exhibits a drastic improvement of the cell efficiency mainly by an increase in the open‐circuit current and fill factor. However, when the Na content is too high, it can deteriorate the cell properties and performance. Nonetheless, it is still beneficial when compared with a cell without Na inside. Here, we therefore use electron backscatter diffraction, atom probe tomography, and admittance spectroscopy to understand why Na starts to deteriorate the properties when inserted excessively. More exactly, it is shown that a moderate addition of Na strongly decreases the open‐circuit voltage (VOC) deficit, whereas the opposite happens when the Na content is too high. Interestingly, this cell with deteriorated VOC value and characterized by a very high Na content exhibits a high density of not only grain boundaries and dislocations but also of Na‐rich clusters. These clusters may host a high concentration of deep defects and trap the electrons within the CIGS bulk. At this stage, Na still has its beneficial effects, but the cell properties start to deteriorate compared to the cell with a moderate content of Na, especially when found as clusters in the bulk. In conclusion, this work clearly demonstrates the dual effect of Na in the CIGS absorber.
Funder
Bundesministerium für Wirtschaft und Klimaschutz
Subject
Electrical and Electronic Engineering,Energy Engineering and Power Technology,Atomic and Molecular Physics, and Optics,Electronic, Optical and Magnetic Materials