Cu₂ZnSnS₄-based thin films and solar cells by rapid thermal annealing processing

In this study, kesterite Cu₂ZnSnS₄ (CZTS) absorber layers were fabricated by DC magnetron sputtering deposition of metallic Cu-Zn-Sn precursors, followed by an annealing treatment in sulfur vapor atmosphere at 600 °C for 3 min using rapid thermal processing (RTP). Three types of stacked metallic films were prepared and included pre-annealing of Cu-Sn stacks in order to induce preferential Cu-Sn alloying. The chemical composition of the sulfurized films was obtained by X-ray fluorescence (XRF) before and after etching the samples in KCN solution. All CZTS thin films are found to be Cu-poor and Zn-rich. Structural characterizations were performed by X-ray diffraction (XRD) and Raman spectroscopy to investigate the impact of pre-annealing on the structural properties of the precursors and final CZTS films. Glow discharge optical emission spectroscopy (GDOES) shows that pre-annealing of the precursors can improve depth homogeneity of the CZTS films. Photoluminescence spectra and the optical band gap energy values are compatible with literature. Selected samples were processed to solar cells and characterized. - Highlights: • Metallic precursors were fabricated on Mo-coated glass by DC magnetron sputtering. • Cu, Zn, and Sn thin films converted to Cu₂ZnSnS₄ using rapid thermal processing. • Cu₂ZnSnS₄ thin films showed Cu-poor and Zn-rich composition. • Pre-annealing process of Cu-Sn enhanced homogeneity of Cu₂ZnSnS₄ thin films. • The best solar cell had conversion efficiency of 2.2%.