Microwav-assisted synthesis and optimization of ACo2S4 tertiary metal sulfides and their use as counter electrodes in dye sensitized solar cells

In this thesis, ACo2S4 (A: Zn+2 and Fe+2) ternary metal sulfides were successfully synthesized for the first time using microwave method and used as counter electrode (CE) in Dye Sensitive Solar Cells (DSSC). In the studies preformed, to determine the most suitable microwave radiation duration; in the first stage, the metals (ACo2, A: Zn+2 and Fe+2) were exposed to microwave radiation separately for 5, 10, 15 and 30 min, and in the second stage, after the sulfur source was added the microwave radiation was applied to the materials formed (ACo2S4, A: Zn+2 and Fe+2) separately for 10, 20 and 40 min. Optimum synthesis times were determined by analyzing X-ray diffraction (XRD) for the 24 different powder samples obtained. On the other hand, syntheses were made at 500, 700, 900 and 1200 W radiation powers at appropriate exposure times to determine the most appropriate microwave radiation power. Samples produced were characterized by XRD and scanning electron microscope (SEM), and the most suitable power value was determined. It was determined that the most suitable times for the synthesis of ternary metal sulfides were 15 and 20 d, respectively, and the most suitable power was 900 W. Physical, elemental and morphological measurements of ternary metal sulfides synthesized under optimum conditions were taken. It was determined from the analyzes performed that the ternary metal sulfides possesed high crystal quality and conductivity, were synthesized without impurities, had the desired stoichiometry (ACo2S4) and consisted of nanosized particles (~40 nm). Besides, the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were taken by coating the ternary metal sulfides with fluorine-doped tin oxide (FTO) substrates by spin coating method. From the results obtained, CE with ZnCo2S4 structure exhibited a higher electrocatalytic activity compared to the reference CEs platinum (Pt) and CoS while CE with FeCo2S4 structure showed a similar performance to CE with Pt and higher than that with CoS. Finally, DSSCs were produced using the produced CEs and the current density-voltage (J-V) curves were measured. While DSSC with ZnCo2S4 structure exhibited a conversion efficiency of 7.83%, the efficiencies of FeCo2S4, Pt and CoS CE-based cells were calculated to be 6.32%, 7.11% and 5.08%, respectively.