The possibility of synthesis of CZTS thin films on glass substrates from DMSO precursor solutions containing various quantity of copper ions was investigated. The dependence of composition of final CZTS compounds obtained from precursor solutions with different copper ion concentration in DMSO was shown. It was obtained that with the introduction of a low additive of copper ion concentration one can synthesize CZTS thin films with kesterite structure as well as with secondary phases (tin sulfides of SnS, Sn2S3). The increase of the concentration of copper ions in DMSO precursor solution promotes the formation of CZTS thin films with kesterite phase and the minimum content of impurities.