In-Operando Nanoscale X-ray Analysis Revealing the Local Electrical Properties of Rubidium-Enriched Grain Boundaries in Cu(In,Ga)Se Solar Cells.

Chalcogenide Cu(In,Ga)Se solar cells yield one of the highest efficiencies among all thin-film photovoltaics. However, the variability of the absorber compositions and incorporated alkali elements strongly affect the conversion efficiency. Thus, effective strategies for spatially resolved tracking of the alkali concentration and composition during operation are needed to alleviate this limitation. Here, using a hard X-ray nanoprobe, we apply a synergistic approach of X-ray fluorescence analysis and X-ray beam-induced current techniques under operando conditions. The simultaneous monitoring of both compositional and functional properties in complete solar cells illustrates the exceptional capabilities of this combination of techniques in top-view geometry, where high spatial resolution resulted even underneath the electrical contacts. Our observations reveal Rb agglomerations in selected areas and compositional variations between different grains and their boundaries. The concurrent detection of the functionality exhibits negligible effects on the collection efficiency for Rb-enriched grain boundaries in comparison to their neighboring grains, which indicates the passivation of detrimental defects.