In-situ X-ray diffraction annealing study of electroplated and sputtered Cu-In-Ga precursors for application to sequential Cu(In,Ga)Se2 processes

We study by in-situ X-ray diffraction (XRD) in a unique, custom-made furnace mimicking an industrial setup, the effect of pre-annealing on electroplated and sputtered thin films of Cu-In-Ga, as precursor material for Cu(In,Ga)(S,Se)2 (CIGS)-based solar cells. In the first part of the paper, the properties of the as-deposited precursors are investigated. We propose a mechanism to explain how indium, despite being deposited before gallium, systematically ends up on top of the stack. The shelf time at room temperature is also shown to strongly affect the metallic phases present in the precursor, unlike sputtered precursors where only minor changes can be observed. These results are then used as input for the second part of the paper. In the second part, pre-annealing experiments up to 550 °C are carried out on the electroplated and sputtered precursors at atmospheric pressure in an inert N2 atmosphere and analysed by in-situ XRD. We find that above the decomposition temperature of Cu11In9 (310 °C) and below around 520 °C, mainly Cu9(In,Ga)4 is left in all precursors, regardless of the phases initially present at room temperature or whether the samples were electroplated or sputtered. We validate these findings for a fast heating ramp to 350 °C, followed by a dwell, as is commonly applied in many CIGS fabrication processes. The implications of these results to high quality CIGS manufacturing are then discussed.