Cu2ZnSn(S,Se)4 (CZTSSe) based thin-film solar cells have attracted growing attention because of their earthabundant and non-toxic elements. However, because of their large open-circuit voltage (Voc)-deficit, CZTSSe solar cells exhibit poor device performance compared to well-established Cu(In,Ga)(S,Se)2 (CIGS) and CdTe based solar cells. One of the main causes of this large Voc-deficit is poor absorber properties for example, high band tailing properties, defects, secondary phases, carrier recombination, etc. In particular, the fabrication of absorbers using physical methods results in poor surface morphology, such as pin-holes and voids. To overcome this problem and form large and homogeneous CZTSSe grains, CZTSSe based absorber layers are prepared by a sputtering technique with different RTA conditions. The temperature is varied from 510 °C to 540 °C during the rapid thermal annealing (RTA) process. Further, CZTSSe thin films are examined with X-ray diffraction, X-ray fluorescence, Raman spectroscopy, IPCE, Energy dispersive spectroscopy and Scanning electron microscopy techniques. The present work shows that Cu-based secondary phase formation can be suppressed in the CZTSSe absorber layer at an optimum RTA condition.