## 3 Results and Discussion
### Process to Control the Film Characteristics of SnS Film Using Seed Layer
As can be seen in Figure 6a, the contact angle of the SnS\({}_{2}\) seed layer was also larger than the contact angle of the SiO\({}_{2}\) substrate. However, because the influence of the lattice mismatch was dominant, the grain size was not reduced as in sample B. In addition, the contact angle of the SnS\({}_{2}\) seed layer did not change significantly after vacuum annealing. Therefore, the strain of the film due to the surface energy change is expected to be negligible. The reduction of lattice mismatch due to the phase transition of the SnS\({}_{2}\) seed to the SnS phase could be discussed, but it also has lower priority. This is because the SnS\({}_{2}\) seed layer deposited as the crystallized thin film requires more activation energy for transition to SnS than a-SnS\({}_{2}\) film. Therefore, the transformation rate of the SnS\({}_{2}\) seed is slower than that of the a-SnS\({}_{2}\) film. Because the SnS process used a seed layer, sample B formed a denser film compared to sample A. The process using the SnS seed layer can reduce the problems of film defects, such as shunt loss in solar cells. However, the increase in grain boundaries due to the reduction in grain size resulted in a slight decrease in electrical properties, as shown in Table 3. The resistivity and mobility of sample B were \(6.67\times 10^{-2}\)\(\Omega\)m and \(11.50\) cm\({}^{2}\)/Vs, respectively. The resultant electrical properties of sample B were lower than the resistivity of \(4.96\times 10^{-2}\)\(\Omega\)m and the mobility of \(32.67\) cm\({}^{2}\)/Vs of sample A. Sample C had a resistivity of \(5.13\times 10^{-2}\)\(\Omega\)m and mobility of \(8.97\) cm\({}^{2}\)/Vs, which is lower than that of sample A. The electrical properties of sample C were affected by vertically grown SnS grains and porous film characteristics. However, sample C had the advantage of film shape with increased reactive sites compared to conventional SnS films. Thus, sample C could be applied to  
Figure 5: (**a**) Schematic diagram of the SnS film process sequence with a seed layer. (**b**) XRD patterns of seed layers and vacuum annealing result of seed layers. (**c**) XRD patterns of the SnS films with various seed layers. (**d–f**) SEM images of SnS films obtained by annealing a-SnS\({}_{2}\) films, including various seed layers, at vacuum atmosphere. electrochemical devices driven by ion exchange. Additionally, all the SnS films in this process showed carrier concentrations of the order of \(10^{19}\) cm\({}^{-3}\), which are higher than those of known SnS film studies by ALD due to the low resistivity via high film thickness. In practice, studies on thick SnS films have shown high carrier concentration between \(10^{18}\)-\(10^{19}\) cm\({}^{-3}\)[35; 36; 37]. The process using seed layers requires additional modification of seed layer thickness. The use of SnS and SnS\({}_{2}\) seed layers has the advantage that the entire thick SnS film formation process can be carried out continuously in one chamber. However, the growth rates of the seed layers were relatively lower than that of a-SnS\({}_{2}\) film. Therefore, further research on the effects of thinner seed layer is needed, and optimal SnS film properties for various energy device applications should be determined by reducing the thickness of the seed layer.