Elektrokimyasal sentez koşullarının çinko oksit ve demir oksit filmlerin morfoloji ve özelliklerine etkilerinin incelenmesi

Main objective of this study is to explore hydrothermal-electrochemical deposition (HED) as a means of developing semiconductor metal oxide films as photoelectrodes for electricity and hydrogen production with solar energy. The first part of this dissertation is devoted to preparation of ZnO films of various size and shape as efficient photoelectrodes by manipulating HED parameters and using electrodeposition as a means to coat sensitizers on ZnO with better electrical contact for cells with enhanced performance. It was observed that 1-D ZnO rods are obtained regardless of precursor (and/or KCl) concentration via HED and the adjustment of concentration provides control on the rod diameter. Increasing precursor concentration resulted in enhanced c-axis orientation and increase in the rod diameter. Moreover, photoelectrochemical sensitivity is enhanced both with improved c-axis orientation and increased rod diameter. A short circuit current density of 2.08 mA/cm2 and an open circuit potential of -1.32 V have been achieved for the ZnO100/CdS21 electrode resulting in an overall solar-electrical energy conversion efficiency of 0.93 %. Since morphological details of a semiconductor electrode such as size, shape, and connectivity of the particles often dictate physical properties, understanding and controlling the morphological aspects of polycrystalline electrodes is critical in producing highly efficient devices. Hence, preparation of ZnO structures in various shapes in synergistic effect of the growth-modifier molecules and HED is also demonstrated. It has been presented that by adjusting [MnCl2] in deposition bath, diameters of rods can be tuned. HED also provides a single-step synthesis route for hierarchical ZnO architectures by modifying [Cd(CH3COO)2/Zn(II)]. HED allows growth of heterogeneous ZnO-Co nanostructures with Co-rich spheres on a zinc rich matrix, where the degree of phase separation and the quantity of the initial Co rich spheres are determined by Co(II) concentration. Electrochemical deposition is studied as a quicker and cheaper alternative to deposit CdS and Ag2S coatings on ZnO nanorod arrays. Photoresponse tends to increase with deposition time for CdS coatings due to the increased amount of visible-light sensitive CdS on ZnO film. However, generated photocurrent is reduced by prolonged deposition. A short circuit current density of 1.42 mA/cm2 and an open circuit potential of -1.391 V have been achieved for the annealed Mn_doped CdS/ZnO electrode resulting in an overall power conversion efficiency of 0.81 %. Ag2S/ZnO photoelectrodes exhibit considerably increased and widened light absorption but lower power-conversion efficiency, most probably due to ZnO degradation during deposition step. Furthermore, in an effort to produce buffer layers for solar cells with enhanced photoactivity, photoelectrochemical properties of mixed semiconductor CdS–ZnS films synthesized by electrochemical deposition is explored. The best performing film exhibited a short circuit current density of 1.31 mA/cm2 and an open circuit potential of -0.99 V with an overall power conversion efficiency of 0.6 %. The second part of this thesis is devoted to investigate physical and photoelectrochemical properties of α-Fe2O3 films grown by HED and to the synthesis α-Fe2O3 particles of varying size and shape via HED in the presence of growth-modifier molecules. It is discovered that HED enables production of crystalline α-Fe2O3 phase without thermal annealing as opposed to electrodepositions reported at ambient temperature. Photoelectrochemical studies demonstrated that higher performance can be obtained with the films prepared via HED. Net photocurrent density of 23.6 µA/cm2 is obtained in 0.1 M NaOH under 1 sun conditions at 1.23 V vs NHE with the film prepared from a bath containing 0.05 M FeCl2 and 0.1 M NaCH3COOH via hydrothermal-electrodeposition with a photocurrent onset potential of 0.96 V vs NHE. Moreover, α-Fe2O3 with different morphologies, including worm-like, spherical, rhombohedral, square planar particles, and platelets, were obtained when HED is used together with growth-modifying species such as CH3COO-, Ce3+ and F-.