On microscopic compositional and electrostatic properties of grain boundaries in polycrystalline $CuIn1−xGaxSe2$

We report on the microscopic characteristics of polycrystalline $CuIn1−xGaxSe2$ thin films probed with Auger electron spectroscopy, cathodoluminescence spectroscopy, secondary ion mass spectrometry, and work function measurements. Confirming theory, we find a substantial reduction in Cu content from grain interior to boundary and a $p$-type potential barrier that acts to reduce hole recombination. Such compositional and electrostatic variations between grain boundaries and grain interiors in $CuIn1−xGaxSe2$ solar cell absorber layers may improve the overall photovoltaic efficiency. The high degree of intergranular inhomogeneity emphasizes the importance of detailed grain-by-grain analysis. These results show that careful specimen preparation and ultrahigh vacuum conditions, coupled with nanoscale instrumental resolution, are pivotal for such analysis.