Comprehensive Study of Growth Mechanism and Properties of Low Zn Content Cd1-xZnxS Thin Films by Chemical Bath

Abstract

Cd 1-x Zn x S thin films have been studied extensively as window layers for solar cell applications. However, a mismatch between the Cd 1-x Zn x S and copper-indium-gallium-selenide absorber layers increases with Zn film concentration, which reduces the device efficiency. In this work, Cd 1-x Zn x S thin films with low Zn concentrations were analyzed. The effect of the addition of different molar Zn concentrations to the reaction mixture on the growth mechanism of Cd 1-x Zn x S thin films and the influence of these mechanisms on structural, optical and morphological properties of the films has been studied. Cd 1-x Zn x S thin films were synthesized by chemical bath deposition using an ammonia-free alkaline solution. Microstructural analysis by X-ray diffraction showed that all deposited films grew with hexagonal structure and crystallite sizes decreased as the Zn concentration in the film increased. Optical measurements indicated a high optical transmission between 75% and 90% for wavelengths above the absorption edge. Band gap value increased from 2.48 eV to 2.62 eV, and the refractive index values for Cd 1-x Zn x S thin films decreased as the Zn increased. These changes in films and properties are related to a modification in growth mechanism of the Cd 1-x Zn x S thin films, with the influence of Zn(OH) 2 formation being more important as Zn in solution increases.

Optimization of Zn concentration in chemically deposited (Cd x –Zn1−x )S nanocrystalline films for solar cell applications

“…Rodriguez et al [46] made a theoretical investigation of various properties, including XRD of Cd 1-x Zn x S thin films prepared by CBD in detail and concluded that for each sample, the lattice strain contributes to the peak broadening and with increasing Zn concentration, there is noticed a change in crystallite size that contributes to the peak broadening.…”

Formation of wide-bandgap, highly transparent and compact Cd1−xZnxS films with dynamically controlled pH in chemical bath deposition

“…If the k sp of metal sulfides (Zn/CdS) is exceeded, ( k sp,CdS = 10 −28 and k sp,ZnS = 10 −25 ), the existing free ions (Cd 2+ , Zn 2+ and S 2− ) form metal sulfide particles in the solution. 43 These particles form clusters and eventually adsorb on the substrate surface to form Cd 1− x Zn x S films – a process known as the homogeneous formation mechanism. Reactions involved in this mechanism can be written as follows: 38,44 Cd(NH 3 ) n 2+ ⇌ Cd 2+ + n NH 3 Zn(NH 3 ) n 2+ ⇌ Zn 2+ + n NH 3 SC(NH 2 ) 2 + 2OH − ⇌ S 2− + CN 2 H 2 + 2H 2 OThe growth of Cd 1− x Zn x S films greatly depends on these metal–amino complex ions' stability constants ( C ).…”

Effective clay material enriched with thiol groups for Zn(II) removal from aqueous media: A statistical approach based on response surface methodology

“…On the other hand, an increase in pH of Zn(II) solution results in the reduction of positive surface charge, indicating that the electrostatic attraction between the negatively charged adsorbent surface and the positively charged Zn(II) ions. It is true that the predominant species of Zn(II) is Zn(OH)2 at pH > 8, corresponding that decrease in adsorption yield compared to neutral conditions [2,20]. Figure 5.…”