Enhancing microstructural and optoelectronic properties of CZTS thin films by post deposition ionic treatment

•Na and Sn ionic treatment for CZTS thin films were carried out.•Microstructural and optoelectronic properties were improved upon ionic treatment.•Tin loss was suppressed and carrier concentration was increased after ionic treatment. Kesterite structure Cu2ZnSnS4 (CZTS) was deposited by RF magnetron sputtering, followed by ionic treatment using 0.25 M of NaF and 0.05 M of SnCl2 before being sulphurized. The ionic treatment using sodium and tin improved the structural, morphological, optical, and electrical properties of the CZTS thin films. The added Na and Sn before the sulphurization process promoted the growth of the main peak in (112) direction, indicative of improved crystallinity of the samples. Homogeneously large and smooth grains were also observed. The bandgap was found to be 1.5 eV with a corresponding Urbach energy value of 0.167 meV. The Urbach energy for the treated samples is lower than the untreated, signifying that the treated samples are less disordered and possessed better crystallinity. The carrier concentration was found to have increased by two orders of magnitude to 1.97E+15 cm−3.