Influence of Low-Temperature Annealing on the Structure and Chemical Composition of Cu2ZnSnS4 Films Deposed on Flexible Polyimide Substrates

The Cu2ZnSnS4 (CZTS) films are deposited onto flexible polyimide substrates by spraying inks containing nanoparticles with subsequent low-temperature annealing at 200°C for 10–120 min in an argon atmosphere. By the methods of X-ray diffractometry and Raman spectroscopy, it can be shown that the nanoparticles and films contain the kesterite phase with small amounts of inclusions of the CuxS and CuxSnySz phases. Increasing the duration of growth of nanoparticles and time of annealing of the films, we improve the crystalline quality of kesterite, i.e., of their main phase. It is shown that the obtained CZTS films are nanostructured and do not suffer cracking even after 50 events of bending in an area of 10 × 10 μm. By applying the method of energy-dispersive X-ray analysis to determine the chemical composition of the samples, we show that the nanoparticles and CZTS films contain excess amounts of copper and sulfur but are depleted of zinc. By analyzing the optical characteristics of the layers, we conclude that the width of forbidden zone for synthesized materials is Eg = (1.4–1.5) ± 0.2 eV, which coincides with the available data. The obtained CZTS films are promising for applications as absorbing layers of solar cells of the third generation.