Hyo Rim Jung

Evolution of detrimental secondary phases in unstable Cu2ZnSnS4 films during annealing

The formation and phase evolution of Cu-S based compounds in kesterite Cu2ZnSnS4 (CZTS) absorbing thin films is a critical factor affecting the performance of these materials in thin film solar cells (TFSCs). However, to the best of our knowledge, few studies have investigated the segregation of Cu-S based compounds in kesterite thin films during the sulfurization process. In this study, stacked Cu/SnS2/ZnS precursor thin films were annealed to systematically study the segregation and phase evolution of Cu-S based compounds in kesterite thin films subjected to functional sulfurization times at 550°C. The stacked precursor thin films appeared to be fully transformed to the pure kesterite phase when the sulfurization times are over 30 min. when analyzed using X-ray diffraction and Raman spectroscopy. However, transmission electron microscopy (TEM) characterization revealed that Cu-S based compounds segregated in the kesterite CZTS thin films annealed for 120 min. at 550°C. Based on the experimental results obtained for functional sulfurization times, a mechanism for Cu-S based compounds segregation and the phase evolution process is proposed.

Size and shape controlled hydrothermal synthesis of kesterite Cu2ZnSnS4 nanocrystals

Quaternary kesterite Cu2ZnSnS4 (CZTS) nanocrystals (NCs) have been synthesized using a simple, size and shape tunable, and low-cost hydrothermal technique without using toxic chemicals. The size and shape of the kesterite CZTS NCs could be controlled by using different complexing agents including non-complexing agent, hydrazine hydrate, tri-sodium citrate (Na3-citrate), and tetra-acetate disodium salt (Na2EDTA). The hydrothermally synthesized CZTS nanocrystals showed a kesterite structure, high optical absorption, and suitable band gap energy characteristics, indicating potential for application to thin film solar cells.