## 4 Applications of Bulk SnS
have shown all solid state inorganic-organic heterojunction solar cells with the structure: FTO/TiO\({}_{2}\)/SnS/P3 HT/Ag, where SnS was deposited using chemical bath deposition (CBD) as a sensitizer and P3 HT working as both a hole transporter and electron donor. An efficiency of 2.8% was achieved, with a high V\({}_{\text{OC}}\) of 0.85 V obtained. [PERSON] et al. [71] have reported hybrid solar cells with ITO/TiO\({}_{2}\)/SnS/P3 HT/MoO\({}_{3}\)/Ag architecture, where SnS was deposited by spin coating, using SnCl\({}_{2}\) and thioacetamide (TAA) in pyridine as the tin and sulfur sources, respectively. The SnS layer was infiltrated with a P3 HT solution left for 30 s on top of the SnS layer before spin coating. The device was completed via the thermal evaporation of MoO\({}_{3}\) and Ag on top of the SnS/P3 HT layers. An efficiency of 1.2% was obtained for solar cells produced via this preparation method [72]. In another study, [PERSON] et al. have fabricated SnS \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Role of SnS Layer** & **SnS Growth Method** & \(\eta\)**(\%)** & **V\({}_{\text{OC}}\) (V)** &
\begin{tabular}{c} \(\text{Jsc}\) \\ **(m/cm\({}^{2}\))** \\ \end{tabular} & **FF (\%)** & **Device Area (cm\({}^{2}\))** & **Reference** \\ \hline Absorber & ALD & 4.36 & 0.37 & 20.2 & 58 & 0.24 & [8] \\ \hline Absorber & TE & 3.88 & 0.33 & 20.6 & 56.28 & 0.25 & [69] \\ \hline Absorber & PCVD & 2.90 & 0.26 & 24.9 & 44.4 & 0.25 & [70] \\ \hline CE & TD & 6.56 & 0.74 & 17.7 & 50 & 0.25 & [9] \\ \hline CE & CoSP & 2.00 & 0.46 & 10.8 & 40 & 0.25 & [10] \\ \hline Sensitizer & CBD & 2.81 & 0.85 & 7.4 & 45 & 0.04 & [71] \\ \hline Sensitizer & Spin Coat & 1.20 & 0.27 & 11.6 & 38 & NA & [72] \\ \hline Sensitizer & Spin Coat & 3.00 & 0.31 & 24.8 & 39 & 0.1 & [5] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: SnS-based solar cells: role of SnS, growth methods and performance parameters. Key: CE—counter electrode; ALD—atomic layer deposition; TE, thermal evaporator; PCVD, pulsed chemical vapor deposition; TD, thermal decomposition; CoSP, continuous spray pyrolysis; CBD, chemical bath deposition. thin film solar cells with glass/FTO/planar-TiO\({}_{2}\)/mp-TiO\({}_{2}\)/SnS/P3 HT/PEDOT:PSS/Ag architecture that incorporated mesoporous TiO\({}_{2}\)/SnS/P3 HT heterojunctions. The SnS layer was deposited using an environmentally friendly solution-based spin coating. The film morphology and surface coverage obtained could be tuned by modifying the precursor solution composition and deposition conditions. The PEDOT:PSS layer was inserted between P3 HT layer and the Ag electrode to improve the V\({}_{\text{OC}}\) and J\({}_{\text{SC}}\) of the devices, which also enables efficient hole extraction while protecting the organic material during the metal contact evaporation. This leads to an increase in the power conversion efficiency from 2.6% to 3.0%. It is believed that highly efficient and more stable devices could be produced by further optimisation of the SnS film morphology, as well as through device engineering (Figure 4) [5]. Bulk SnS has also been used widely for thermoelectric energy generation via the Seebeck effect. [PERSON] et al. have synthesised SnS via a chemical precipitation method. This method involved the reaction of a solution of SnCl\({}_{2}\), ethylenediamineetraacetic acid (EDTA), and triethanolamine [73] with a solution of sodium hyposulfide (Na\({}_{2}\)S\({}_{2}\)O\({}_{3}\)) dissolved in deionised water and ammonia. Annealing of the microstructure was found to change the SnS from the orthorhombic \(\alpha\)-phase to the tetragonal \(\beta\)-phase at 858 K. A ZT value of 0.52 for polycrystalline SnS with no intentional doping at 873 K was obtained by [PERSON] et al. [74] A ZT value of 1.6 at 823 K was obtained by [PERSON] et al. from mechanically alloyed, spark plasma sintered SnS. This enhancement was obtained predominantly by tuning carrier concentration via doping; stoichiometric ratios and sintering temperatures had a less significant effect [29].