  The chalcopyrite Cu(In,Ga)S${_2}$ has gained renewed interest in recent years
due to the potential application in tandem solar cells. In this contribution, a
combined theoretical and experimental approach is applied to investigate stable
and metastable phases forming in CuInS${_2}$ (CIS) thin films. Ab initio
calculations are performed to obtain formation energies, X-ray diffraction
patterns, and Raman spectra of CIS polytypes and related compounds. Multiple
CIS structures with zinc-blende and wurtzite-derived lattices are identified
and their XRD/Raman patterns are shown to contain overlapping features, which
could lead to misidentification. Thin films with compositions from Cu-rich to
Cu-poor are synthesized with a two-step approach based on sputtering from
binary targets followed by high-temperature sulfurization. It is discovered
that several CIS polymorphs are formed when growing the material with this
approach. In the Cu-poor material, wurtzite CIS is observed for the first time
in sputtered thin films along with chalcopyrite CIS and CuAu-ordered CIS. Once
the wurtzite CIS phase has formed, it is difficult to convert into the stable
chalcopyrite polymorph. CuIn${_5}$S${_8}$ and NaInS${_2}$ accommodating
In-excess are found alongside the CIS polymorphs. It is argued that the
metastable polymorphs are stabilized by off-stoichiometry of the precursors,
hence tight composition control is required.
