Alkali diffusion in CIGS solar cells studied by gallium and neon SIMS

Secondary ion mass spectrometry (SIMS) was used to study alkali element diffusion in high-efficiency copper indium gallium selenide (CIGS) solar cells. Traces of alkali elements in the CIGS active layer are known to have a positive impact on cell efficiency. SIMS depth profiling through the complete layer structure – from front electrode to substrate – was conducted by time of flight SIMS in a gallium FIBSEM. As expected, Na and K diffusion into the CIGS active layer was present on samples grown on soda lime glass as opposed to reference samples grown on alumina. Furthermore, high resolution neon beam SIMS in a HIM (helium/neon ion microscope) was done on cross sections of the sample revealing the alkali element distribution in the CIGS layer with unprecedented spatial resolution.