In-situ XRD study on the selenisation parameters driving Ga/In interdiffusion in Cu(In,Ga)Se2 in a versatile, industrially-relevant selenisation furnace

The selenisation of Cu-Ga-In metallic precursors is investigated by in-situ X-Ray Diffraction (XRD) in a selenisation tool which mimics at the laboratory scale an industrial tool (thus fully scalable) and allows fine control over the selenisation parameters and reproducibility. In this setup, the interdiffusion of Ga and In was significantly accelerated by decreasing the Se crucible temperature or increasing the sample temperature. Applying a lower Se crucible temperature yielded a very fast initial interdiffusion that quickly reached a steady-state, non-flat Ga/(Ga + In) (GGI) depth profile. On the other hand, the higher crucible temperature tested led to a slower interdiffusion which kept evolving to a flatter GGI profile after a sufficiently long dwell time at the maximum temperature. Strategies to gain better control over the GGI profile, and hence bandgap profile, are discussed. The results indicate that the versatility of the setup is key to achieving fine control over the GGI depth profile, which is particularly relevant today, when new alkali doping strategies are being introduced.