**3.3.2 SnO2:F-SnS2 gradually grown layers**

36 Solar Cells – New Aspects and Solutions

Fig. 7. Photoconductivity spectra versus time of ZnO/FTO (d), AZO/FTO (e), IZO/FTO (f).

Tin oxide (SnO2) is an *n*-type VI-II oxide semiconductor with a wide band gap (*E*g = 3.6 eV). Because of its good opto-electrical properties, and its ability to induce a high degree of charge compensation, it is widely used as a functional material for the optoelectronic devices, gas sensor, ion sensitive field effect transistors, and transparent coatings for organic light emitting diodes (Onyia & Okeke, 1989; Wang et al., 2006; Lee & Park, 2006; Yamada et al., Kane & Schweizer,1976).

In the last decades, pure and doped tin oxide compounds, prepared by several techniques (Manorama et al., 1999; Bruno et al., 1994; Brinzari et al., 2001; Wang et al., 2002) have been used for the preparation of high performance gas sensing and light emitting devices layers ( Barsan, 1994; Goepel & Schierbaum, 1995; Ramgir et al. ,2005).

SnO2 thin films are generally prepared using methanol CH4O: 1.0 L, demineralised water and anhydrous tin tetrachloride SnCl4. Formation of pure SnO2 is resulting from the endothermic reaction:

$$\underbrace{SnCl\_4}\_{4} + 2\underbrace{II\_2O}\_{\text{(потной, 410\text{ °C})}} \xrightarrow[\longleftrightarrow \text{ }]{\text{(потной, 410\text{ °C})}} \underbrace{SnO\_2}\_{\text{(---)}} + 4\underbrace{IICl\_4}\_{\text{(---)}}$$

Approximately 0.9 µm-thick SnO2 thin films are generally deposited on glass, under an approximated substrate temperature *T*s=440°C.

XRD patterns of the as-grown SnO2 films are shown in Fig. 9. Diagram analysis shows that the layers present a first set of (110)-(101)-(200) X-ray diffraction peaks followed by more important pair (211)-(301). According to JCDPS 88-0287 (2000) standards, these patterns refer to tetragonal crystalline structure.

It was reported by Yakuphanoglu (2009) and Khandelwal et al. (2009)that SnO2 films structure depends wholly on elaboration technique, substrate material and thermal treatment conditions. This feature was also discussed by Purushothaman et al. (2009) and Kim et al. (2008) who presented temperature-dependent structure alteration of the SnO2 layers.

Atomic force microscopy (AFM) 3D images of the SnO2 are presented in Fig. 10.

The layers present a pyramidal-clusters rough structure, which is characteristic to many Snlike metal oxides. This observation confirms the XRD results.

A New Guide to Thermally Optimized Doped Oxides Monolayer

and

mini-layer is n-type (fig 11-b).

Spray-Grown Solar Cells: The Amlouk-Boubaker Optothermal Expansivity

radii ratio is around 0.96). The obtained layers are n-type (Fig 11-a)

Fig. 11. TCO monolayer-grown: cell elaboration protocol

**3.3.3 A sketch of the thermally optimized new monolayer grown cell** 

mechanical performance than CuInS.

(M=Cu, Ag,..) hetero-junction.

In the second reaction, ammonium florid acts on the deposited (and heated) tin tetrachloride

Hence, the first step of the protocol is indeed elaboration of the precursor SnO2: F layer. In the second step, this layer is subjected to local annealing in a highly sulfured atmosphere (Fig 11-b). Under specific experimental conditions (Temperature, pressure, exposure time) SnS2 compound appears selectively at the top of the precursor SnO2: F layer. This obtained

Finally, a neutral masking sheet is applied to the free surface in order to deposit copper (Cu) by evaporation, controlled dipping or even direct mechanical spotting. Due to the metallic diffusive properties, a multiphase CuSnS (Cu2SnS3,Cu3SnS4,Cu…) conducting compound appears at the free surfaces (Fig 11-c). This compound has been verified to have better

The first prototype of the proposed TCO monolayer-grown Solar cell is presented in Figure 12. The procedure can be applied to other oxides, namely SbxOy, SbxSy/MSbO

by incorporation process due to ionic close electro-negativity and dimension (F-

AB 39

and O2-

Fig. 9. XRD Diagram of SnO2 thin layers prepared at *T*s 440 °C.

Fig. 10. SnO2 layers 3D and 2D surface topography 2D (top) and 3D (bottom).

SnO2:F-SnS2 gradually grown layers have as intermediate precursors SnO2:F layers obtained by spray pyrolysis on glass substrates according to the coupled reactions :

$$\left\{ \left\{ \mathrm{SnCl}\_{4}, \mathsf{5}H\_{2}O \right\}\_{\mathrm{n}} + 2 \,\mathrm{nH}\_{2}O \xrightarrow[\text{Ginzburg gas}]{\mathsf{S}\_{\mathsf{S}\mathsf{org}}} \mathsf{n} \,\underline{\mathrm{SnCl}\_{4}} + \,\quad \left\{ \mathrm{7n} \,\,\overline{H\_{2}O} \right\}\_{\mathrm{n}} $$

and

38 Solar Cells – New Aspects and Solutions

Fig. 9. XRD Diagram of SnO2 thin layers prepared at *T*s 440 °C.

Fig. 10. SnO2 layers 3D and 2D surface topography 2D (top) and 3D (bottom).

by spray pyrolysis on glass substrates according to the coupled reactions :

SnO2:F-SnS2 gradually grown layers have as intermediate precursors SnO2:F layers obtained

7

$$\mathfrak{n}\mathfrak{N}nCl\_4 + \mathfrak{n}\{NH\_4^+, F^-\} + 2\mathfrak{n}H\_2O \xrightarrow[{\text{mobanol}}] {\mathfrak{n}00^\circ C} \mathfrak{n}\underbrace{\mathfrak{N}nO\_2; F}\_{\bullet} + 4\mathfrak{n}\mathfrak{n}\widetilde{HCl} + \mathfrak{n}\mathfrak{N}\widetilde{H}\_2 + \frac{\mathfrak{n}}{2}\widetilde{H}\_2$$

In the second reaction, ammonium florid acts on the deposited (and heated) tin tetrachloride by incorporation process due to ionic close electro-negativity and dimension (F- and O2 radii ratio is around 0.96). The obtained layers are n-type (Fig 11-a)

Hence, the first step of the protocol is indeed elaboration of the precursor SnO2: F layer. In the second step, this layer is subjected to local annealing in a highly sulfured atmosphere (Fig 11-b). Under specific experimental conditions (Temperature, pressure, exposure time) SnS2 compound appears selectively at the top of the precursor SnO2: F layer. This obtained mini-layer is n-type (fig 11-b).

Fig. 11. TCO monolayer-grown: cell elaboration protocol

Finally, a neutral masking sheet is applied to the free surface in order to deposit copper (Cu) by evaporation, controlled dipping or even direct mechanical spotting. Due to the metallic diffusive properties, a multiphase CuSnS (Cu2SnS3,Cu3SnS4,Cu…) conducting compound appears at the free surfaces (Fig 11-c). This compound has been verified to have better mechanical performance than CuInS.

### **3.3.3 A sketch of the thermally optimized new monolayer grown cell**

The first prototype of the proposed TCO monolayer-grown Solar cell is presented in Figure 12. The procedure can be applied to other oxides, namely SbxOy, SbxSy/MSbO (M=Cu, Ag,..) hetero-junction.

A New Guide to Thermally Optimized Doped Oxides Monolayer

Spray-Grown Solar Cells: The Amlouk-Boubaker Optothermal Expansivity

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AB 41

It has been experimented that n-type can be locally and partially transformed into p-WS2, which results in a WO3/WS2 heterojunction, using the same sulfuration procedure detailed above.

Fig. 12. TCO monolayer-grown Solar cell

The case of ZnO has been experimented but raised some problems, in fact it has been recorded that sulfuration process is never complete, and that an unexpected mixture (ZnO)x(ZnS)y takes place.
