Structural characterization of coevaporated Cu(In,Ga)Se2 absorbers deposited at low temperature

Abstract This paper focuses on low temperature (∼390 °C) growth of Cu(In,Ga)Se 2 (CIGS) for high efficiency solar cells. The process developed in this work allows the growth of high quality CIGS thin films on flexible substrates such as polymer foils with lower impurity out-diffusion from the substrate. We carry out advanced analysis of the microstructure of CIGS absorbers prepared using multi-stage coevaporation on polyimide at low temperature leading to state-of-the-art efficiencies exceeding 18%. We also develop a method that can be used to easily interpret the x-ray diffraction data using compositional analysis, when asymmetric or multi-feature peaks are present. This method proves to be particularly useful to rule out in-plane inhomogeneities and undesired phases when in-depth gradients are present. This analysis is combined with electron microscopy and more advanced x-ray analysis (grazing incidence diffraction and pole plots) to create a global model of the film microstructure. We show that the film is composed of at least three stacked layers with different properties and that the microstructure of the layers has an impact on the cell performances. In particular, the short circuit current J sc is strongly related to the intensity of the (112) peak.