Influence of Substrate Temperature and Sulfurization on Sputtered Cu2SnGe(S,Se)3 Thin Films for Solar Cell Application

This work presents the influence of substrate temperature (
${T}_{\text{sub}}$
) and post-sulfurization on compositional, structural, electrical, and optical properties of dual-ion beam sputtering (DIBS)-grown Cu
₂
(Sn,Ge)(S,Se)
₃
(CTGSSe) thin films grown on a soda-lime glass (SLG) substrate using a single target. Post-sulfurization of CTGSSe thin films is carried out in a quartz tube chemical vapor deposition (CVD) system. X-ray diffraction (XRD) analysis reveals that the crystal structure of CTGSSe thin films is preferentially tetragonal with (112) and (204) lattice planes at
$2\theta $
values of 27.3° and 47.3°, respectively. Field-emission scanning electron microscopy (SEM) has emphasized that the high
${T}_{\text{sub}}$
growth resulted in a larger grain size of 87 nm and better thin-film morphology. Spectroscopic ellipsometry (SE) analysis shows the bandgap values of 1.46–1.62 eV by varying
${T}_{\text{sub}}$
from room temperature (RT) to 300 °C. Furthermore, the bandgap widens from 1.56 to 1.64 eV in the CTGSSe thin films due to post-sulfurization.