Control of Zn content and influence on Cu₂ZnSnSe₄ thin-film solar cells fabricated by coevaporation

The influence of the Zn content on the properties of a coevaporated Cu₂ZnSnSe₄ absorber layer was investigated. Cu₂ZnSnSe₄ (CZTSe) precursors deposited with various Zn composition ratios ([Zn]/[Sn] = 103, 1.06, 1,08, 1.17) were annealed using the rapid thermal process without any Se vapor pressure at 590 C to reduce the possibility of volatile SnSe loss. Scanning electron microscope observations showed that the grain size and surface morphology of the CZTSe absorber layer change depending on the Zn content. Furthermore, X-ray diffraction analyses were performed to determine the crystal quality of the CZTSe absorber layer in terms of the full width at half maximum of the characteristic X-ray diffraction peak and texture coefficient. Raman spectroscopy showed a ZnSe secondary phase in the CZTSe absorber layer with excess Zn. The CZTSe solar cell with the optimal Zn content ([Zn]/[Sn] = 106) exhibited a 6.11% conversion efficiency in a 0.42 cm² active area.