Structural, chemical and magnetic properties of pristine and Fe- doped kesterites before and after thermal annealing

Here, we foster the combined use of conventional techniques to obtain a comprehensive structural and chemical characterization of kesterites (Cu2ZnSnS4, Copper-Zinc-Tin Sulfide, CZTS), a class of light-absorbing materials employed in sustainable thin-film solar cells, with magnetometry and Electron paramagnetic resonance (EPR) spectroscopy, to identify the nature of their paramagnetic centers. Iron-doped (CZFTS) and non-doped nanocrystals were synthesized by hot-injection method and then treated at 450°C. The structural analysis evidenced that while the raw CZTS and CZFTS nanocrystals do not show any secondary phase, a minority phase is present in the annealed samples. The complementary distribution of the metal ions in both CZTS and CZFTS was also assessed. Magnetometry and EPR spectroscopy pointed out the formation of paramagnetic vacancies following the high temperature treatment and the successful doping with Iron. This work highlighted the unique capability of a multipronged approach to detect paramagnetic defects in kesterite nanocrystals, which are otherwise challenging to identify using single techniques.