Optical and Structural Characterization of Cd-Free Buffer Layers Fabricated by Chemical Bath Deposition

Abstract

Chemical bath deposition (CBD) is a suitable, inexpensive, and versatile synthesis technique to fabricate different semiconductors under soft conditions. In this study, we deposited Zn(O;OH)S thin films by the CBD method to analyze the effect of the number of thin film layers on structural and optical properties of buffer layers. Thin films were characterized by X-ray diffraction (XRD) and UV-Vis transmittance measurements. Furthermore, we simulated a species distribution diagram for Zn(O;OH)S film generation during the deposition process. The optical results showed that the number of layers determined the optical transmittance of buffer layers, and that the transmittance reduced from 90% (with one layer) to 50% (with four layers) at the visible range of the electromagnetic spectrum. The structural characterization indicated that the coatings were polycrystalline (α-ZnS and β-Zn(OH)2 to four layers). Our results suggest that Zn(O;OH)S thin films could be used as buffer layers to replace CdS thin films as an optical window in thin-film solar cells.

Effect of Order of Reagents Addition on Optical and Structural Properties of CdS Quantum Dot Prepared by Chemical Bath Deposition Technique

“…The thickness of the films was calculated using the following Equation ( 4 Where t is the film thickness, M is the mass of the quantum dots, ρ is the density of the CdS, which is 4.82 g/cm 3 , and A is the area covered by the quantum dots [4].The effect of pH on the as-deposited CdS-QDs thickness is summarized in Table 3. Table 3 shows that the deposition of the films in an acid medium gave rise to generally nonhomogeneous films of low thickness, while in an alkaline medium the deposited CdS-QDs were homogeneous with appreciably high film thickness except at pH 10.These results indicate the importance of a complexing agent in the deposition process of QDs.…”

“…Cadmium sulfide quantum dots (CdS QDs) have been widely studied because of their numerous applications as a window layer in quantum dot photovoltaics [1,2]. It is also very important as a window layer in the highly efficient polycrystalline Copper Indium Gallium Sulfide (CIGS) and copper indium gallium telluride, (CIGT) [3,4], which are n-type semiconductors with wide direct band gap energy and exist in two crystalline phases of hexagonal wurzite and cubic zinc-blend structures with unique high electron affinity [5]. CdS QDs have been used as n-type materials for the formation of a heterojunction in some photovoltaic systems, such as copper indium selenide (CIS) [6], copper indium gallium diselenide (CIGD) [7], and cadmium telluride (CdTe) [8].Quantum dots (QDs) are semiconductor nanocrystals with a typical size of 2-10 nm and whose electrons are confined in three directions.…”

“…A ISSN: 0067-2904 Nwabue et al Iraqi Journal of Science, 2024, Vol. 65, No.3, pp: 1172-1187 number of chemical and physical methods have been used to deposit CdS QDs in alkaline and acidic media [4]. Some of these methods include pulsed direct current magnetron sputtering [5] , metal organic vapour phase epitaxy [10], and chemical solution deposition [4,11,12].…”

“…Although CdS polycrystalline films grown by the CBD method yield a poor crystalline quality in comparison with films deposited by other techniques, they have been proven to be the most suitable for CdTe-based solar cells, as a maximum efficiency of 16.5% has been achieved with a window layer grown by the CBD technique [14]. The simplicity of CBD, its low temperature requirement, cost effectiveness and large area deposition are the reasons why it is a preferred technique for the preparation of QDs with optimal features for device applications [16].The choice of organic complexing agents (OCA) used in QDs preparation affects the optical, solidstate and surface morphological properties of the deposited thin films [4,17]. This study focused on using a tetradentate Schiff base ligand, EDDBP, as a complexing agent in the synthesis of CdS QDs by the CBD method.…”

The chemical process for materials deposition in aqueous solution: a review

“…The formation of the zinc-hydroxide, Zn(OH) 2 , is sometimes undesirable and appears as a consequence of non-appropriate chemical conditions of the solution when ZnS or ZnO are deposited by CBD [205,206]. Some authors report the formation as an impurity generated along with the desirable compound, highlighting the difficulty of its reduction or elimination [207,208]. With the use of the SDDs and the SCs, it is possible to deposit only this compound or to avoid its formation when another compound is wanted to be deposited.…”