# Recent Advances in the Growth and Characterizations of SILAR-Deposited Thin Films
## 2 Metal Sulfide Thin Films
### Copper Tin Sulfide Films  
The XRD studies confirmed that the orthorhombic phase of Cu\({}_{4}\)SnS\({}_{4}\) (CTS) and the cubic phase of Cu\({}_{2}\)SnS\({}_{3}\) could be prepared under hydrogen sulfide (H\({}_{2}\)S) atmosphere and nitrogen and sulfur vapor mixture conditions, respectively. The activation energies were 0.1 eV and 0.06 eV in Cu\({}_{2}\)SnS\({}_{3}\) and Cu\({}_{4}\)SnS\({}_{4}\) films, respectively [32]. The n-type Cu\({}_{2}\)SnS\({}_{3}\) films were prepared on stainless steel in the presence of ethylene diamine tetra acetic acid disodium (Na\({}_{2}\)EDTA), as reported by [PERSON] and co-workers [33] and indicated in Figure 2. The sodium sulfide was used as anionic while copper (II) chloride (CuCl\({}_{2}\)) and tin chloride (SnCl\({}_{2}\)) acted as cationic precursors. The proposed reaction mechanisms are highlighted in Equations (2)-(5). During the formation of thin films, the substrate was immersed in a cationic solution and anionic solution and then rinsed with double distilled water (DDW) to prevent precipitation (Figure 2).  
\[2\text{CuCl}_{2}\ +\text{SnCl}_{2}\to 2\text{Cu}^{+}+6\text{Cl}^{-}+ \text{Sn}^{4+} \tag{2}\]  
\[\text{Na}_{2}\text{S}+\text{H}_{2}\text{O}\rightarrow\text{OH}^{-}+\text{HS}^ {-}+2\text{Na}^{+} \tag{3}\]  
Figure 1: The scheme of SILAR-deposited tin sulfide thin films reproduced with permission from [31], [PERSON], 2017. (**a**) Immersion in the Sn(NO\({}_{3}\))\({}_{2}\) solution. (**b**) Rinse in the distilled water. (**c**) Immersion in the Na\({}_{2}\)S solution. (**d**) Rinse in the distilled water.  
The X-ray photoelectron spectroscopy (XPS) studies highlighted the +1 and +4 in copper and tin, respectively. The XRD and SEM studies showed that the triclinic phase and spherical grains covered the entire surface of the films, respectively. Brunauer-Emmett-Teller and wettability investigations confirmed the mesoporous with the surface area (2.1 m\({}^{2}\)/g) and hydrophilic nature of the obtained films. The surface area is one of the very important parameters used to study light absorption in various incident angles. Cu\({}_{2}\)SnS\({}_{3}\) films were annealed at 350 \({}^{\circ}\)C under 60 min in the sulfur (S) atmosphere [34]. The XRD studies confirmed the amorphous and polycrystalline in the as-deposited and annealed films, respectively. Optical absorption and EDX investigations showed a smaller band gap (1.21 eV) and excess copper (Cu) concentration in the annealed films. The Cu\({}_{2}\)SnS\({}_{3}\) films were deposited onto an indium-doped tin oxide glass substrate, showing uniform morphology and a blackish color [35]. The annealed films (300 \({}^{\circ}\)C in vacuum) indicated higher intensities when compared to as-deposited films based on the XRD studies. The X-ray photoelectron spectroscopy (XPS) confirmed Cu\({}^{1+}\), Sn\({}^{4+}\), and S\({}^{2-}\) in the obtained films. The highest power conversion efficiency (0.11%) and fill factor (30%) were achieved in ITO/CTS/lithium perchlorate/graphite solar cells. The high phase purity of Cu\({}_{2}\)SnS\({}_{3}\) could be deposited onto a soda lime glass substrate [36]. The absorption coefficient was 104 cm\({}^{-1}\) and reflectivity was 10% at 200-600 nm. Cu\({}_{5}\)Sn\({}_{2}\)S\({}_{7}\) and Cu\({}_{3}\)SnS\({}_{4}\) films were prepared onto a glass substrate at a specific speed (400 nm per 60 min) [37]. Researcher findings showed excellent conductivity, a higher absorption coefficient (more than 10\({}^{4}\) cm\({}^{-1}\)), and strong optical absorption in the near-infrared reflectance (NIR) region. The band gap values were 1.45 and 1.47 eV in Cu\({}_{5}\)Sn\({}_{2}\)S\({}_{7}\) and Cu\({}_{3}\)SnS\({}_{4}\), respectively.