Tailoring the phase structure and optical properties of Cu₂ZnSnS₄ nanocrystals through co-substitution of Ag and Fe

Abstract Straightforward two-step heating method, employing oleylamine as the reaction solvent, was utilized to incorporate Ag and Fe into Cu 2 ZnSnS 4 (CZTS) nanoparticles, resulting in the synthesis of (Cu 1-x Ag x ) 2 Fe y Zn 1-y SnS 4 (CAFZTS, where x = 0, 0.2 and y = 0, 0.05, 0.1) nanoparticles under atmospheric conditions. The produced samples underwent comprehensive characterization through techniques such as XRD, Raman spectroscopy, SEM, EDS, TEM, XPS, and UV–Vis–NIR absorption spectroscopy. The findings revealed that the initial CZTS nanoparticles exhibited a wurtzite phase structure. However, with the introduction of Ag and Fe, a gradual transition from the wurtzite phase to the kesterite phase was observed in the nanoparticles’ structure. Notably, when the Ag substitution ratio (x) reached 0.2 and the Fe substitution ratio (y) was set at either 0 or 0.05, the nanoparticles displayed coexistence of both wurtzite and kesterite phases. Conversely, at an Ag substitution ratio (x) of 0.2 and an Fe substitution ratio (y) of 0.1, the nanoparticles exclusively exhibited a kesterite phase. The band gap of the original CZTS nanoparticles was identified as 1.47eV. This value increased to 1.58eV with an Ag substitution ratio (x) of 0.2. Conversely, with Fe substitution ratios (y) of 0.05 and 0.1, the band gap decreased from 1.30 eV to 1.17 eV, respectively. These results demonstrate that the incorporation of Ag and Fe not only alters the mineral phase of CZTS nanoparticles but also provides a means to adjust the band gap.