Characterization of Cu2ZnSnS4 thin films prepared by the sulfurization of co-sputtered metal precursors

Abstract

In this work, we report on the synthesis and characterization of Cu2ZnSnS4 (CZTS) thin films prepared by annealing of co-sputtered metal precursors in sulfur atmosphere. Radio-frequency magnetron sputtering was applied to deposit the metal layers from single metal targets on Mo-coated soda-lime glass substrates. The chemical composition of the precursors was controlled by varying the sputtering working power, resulting in films with various compositions. X-ray fluorescence was used to determine the elemental concentration of these metal films. The metal precursors were then converted into CZTS in a tube furnace using different sulfurization conditions to investigate the effect of the annealing process on the properties of the final CZTS films. Film structural characterization and phase identification results were supported by X-ray diffraction (XRD) and Raman spectroscopy. Surface and cross-sectional film morphology was carried out by scanning electron microscopy (SEM). For the sulfurized films, significant Sn loss was noticed. However, the loss of Sn was successfully controlled by depositing precursors with an excess of Sn. After optimizing the composition of the metal precursor, XRD and Raman scattering results revealed single-phase CZTS films without clear signs of secondary phases. SEM showed improved morphology in the form of dense structures and smooth surfaces for the films sulfurized at 600°C. Our first solar cell, based on a CZTS film originating from a precursor sulfurized at 550°C for 60 min, showed an open-circuit voltage of 471 mV, a short-circuit current density of 9.92 mA/cm-2, a fill factor of 36.9%, and an efficiency of 1.72%.