CuxBiyTez Nanofilmlerin Elektrokimyasal Potansiyel Altı Kodepozisyon Metodu ile Sentezi, Karakterizasyonu ve Potansiyel Güneş Pili Uygulamasının Araştırılması

Abstract

The ternary copper-based chalcogenides CuxByCz (B = Sb, Bi; C = S, Se, Te) is an important class of materials for modern electronics, energy storage, and biomedical devices as they offer flexibility in composition, structure and morphology, which has an influence on band gap control and opto/electronic properties. Composition and size controlled synthesis of these compounds is one of the most important challenges. Therefore, development of low-cost, easy-to-apply techniques that provide control over the growth process of these compounds at the atomic level is so crucial. In the scope of this thesis, synthesis of CuxBiyTez nanofilm, a ternary copper chalcogenide compound, by using underpotential deposition (UPD) based electrochemical codeposition technique (UPCD) was investigated for the first time in the literature. First, the electrochemical behavior of Cu, Bi and Te on gold (Au) electrode in 0.05 M KCl – 0.4 M HCl electrolyte solution in the bulk and UPD regions were demonstrated by cyclic voltammetry (CV) method. Then, the optimum concentration ratio and UPD deposition potentials were determined for simultaneous deposition (codeposition) of elements in a single solution containing Cu, Bi and Te sources via UPCD to form CuxBiyTez compound on Au electrode. Next, various spectrochemical techniques were utilized for the characterization of the CuxBiyTez compound. For this purpose, CuxBiyTez was deposited on Au and ITO coated PET substrates at the optimum UPD potential (vs. 0.075 V Ag/AgCl). The structure, stoichiometry, morphology, bandwidth and electrical properties of the compound were determined by detailed characterization studies. X-ray diffraction (XRD) results showed that the obtained compound exhibited a rhombohedral crystal structure. X-ray photoelectron spectroscopy (XPS) analysis verified that the stoichiometric composition of the compound was 8:1:9 for Cu, Bi and Te, respectively. Vibration modes at wave numbers of 150 cm-1 and 300 cm-1 were recorded for the CuxBiyTez compound using Raman Spectroscopy. Scanning electron microscopy (SEM) images proved that CuxBiyTez deposited on Au substrate were as granular crystallites with a particle size of about 10 nm, and the obtained film was homogeneous, nano-sized and two-dimensional. Ultraviolet and visible spectroscopy (UV-Vis) measurements revelaed the optical bandgap of the nanofilm as 2.12 eV. Moreover, the current-voltage (I-V) characteristics of CuxBiyTez coated on indium tin oxide (ITO) was tested under normal light to evalute the electrical propertiesof the synthesized film. This study successfully demonstrated the formation of CuxBiyTez thin films by UPD-based codeposition method, which offers an inexpensive way and allows the production of semiconductor nanofilms for use in different opto/electronic applications. Finally, the development of a solar cell prototype was demonstrated by forming heterojunctions two different solar cell prototypes were developed by forming p-n heterojunctions between the synthesized n-type material CuxBiyTez with p-type Cu-Te compound, and their relevant photovoltaic properties were investigated.