In-depth compositional uniformity of CuInSe2 prepared by two-stage growth sequences

A high degree of in-depth compositional uniformity is an important prerequisite for obtaining device-quality CuInSe2 absorber films. In general, it is reported that two-stage growth processes lack reproducibility due to material losses during the high-temperature selenization stages. In this study, absorber films were prepared by a typical two-stage process in which selenium-free (In/Cu/In) and selenium-containing (InSe/Cu/InSe) precursors were reacted with H2Se/Ar. Scanning electron microscopy (SEM) studies revealed a significant improvement in the morphological properties of the absorber films in the latter case. X-ray fluorescence (XRF) K-alpha 1,K-2 line intensity measurements of the samples indicated no loss of In or any other element during the selenization stages, irrespective of the precursor alloy considered. The in-depth compositional uniformity of the samples was determined by measuring the XRF K-alpha 1,K-2 line intensities of successively etched samples. For samples obtained from the selenium-free precursors, this in-depth analysis revealed a pronounced separation of the elements: non-uniform Se interdiffusion and a sharp increase in the In concentration towards the Mo back contact. In samples prepared from selenium-containing precursors, the concentration of all three elements remained virtually unchanged as a function of the sample thickness. X-ray diffraction (XRD) studies also revealed a single-phase material with a very strong preferred [112] orientation.