Synthesis, characterization and optoelectronic applications of ZNSand Cu2ZNS4(CZTS) thin films

Zinc sulfide (ZnS) is one of the most important semiconductors for optoelectronic devices. It is generally used as a buffer layer in high-efficiency Cu2ZnSnS4(CZTS) solar cells due to its environmentally friendly properties. All thin films made in this thesis study were synthesized using the sol-gel dip coating technique. In this study, fort the first time, ZnS1-xNaxS, Zn1-xSnxS and Zn1-xLaxS (x=%0-15) thin films were produced by solution-based sol-gel method on glass and Si (physically etched) substrates in a vacuum environment at 6000C. The effect of the Na+, Sn+2 and La+3 and their doping ratios on the structural, optical and luminescence proporties were examined. Similarly, CZTS thin films were grown on the same substrates at different temperatures (400, 450, 500 and 5500C) by the sol-gel metod. The physical properties of both types of the prepared thin films were characterized by XRD, Raman, SEM, AFM, XPS, EDX, mapping, photoluminescence, UV-Vis spectroscopy, Hall effect, current(I)-voltaj(V) measurement systems and solar simulator. The prepared ZnS1-xNaxS, Zn1-xSnxS and Zn1-xLaxS (x=%0-15) thin films have a mixed cubic and hexagonal ZnS polycrytalline phase but have a highly preferred orientation along the dominant (111) cubic plane. Among this film group, it was understood that the crystalline quality. The optical bandgap value and photoluminescence intensy of the ZnS thin film changed with the Na+, Sn+2, La+3 dopant types and ratios. Among these films, the I-V graphs of the films coated on the p/n type Si exhibit non-ohmic behavior, indicating that a p-n juntion was formed. On the other hand, it was observed that the prepared CZTS thin films crystallization varied depending on the annealling temperature and duration. Surface and elemental analysis results showed that CZTS film surface was homogeneous but rough and contained Cu, Zn, Sn and S atoms in certain proportions. Optical measurement reslts showed that the absorption intensity and band gap (1.3-1.8 eV) varied depending on the anneling temperature, duration and the used substrate. In addition, electrical measurements results showed that the CZTS semiconductor had p-type conductivity and at the same duration, I-V measurements of the film samples coated on the n-type Si exhibited non-ohmic behavior. Although no significant efficiency was obtained in the solar cells prepared on p- and n- type Si, only a very low efficiency was obtained in a CZTS based solar cell. The reasons for not achieving a significant efficiency was determined to be leakage current, microcracks in the prepared films and thickness of the absorptive CZTS layer.