Using Non Alkoxide Precursor

Alkoxides are usually very costly. However, this problem can be overcome by using the cheap, commercially available non-alkoxide precursors, namely SnCl4, without further purification or modification. Following procedures are generally followed to prepare pure and modified SnO2 thin films by means of sol-gel technique utilizing non-alkoxide precursors. In the first method [5, 13, 14], tin tetrachloride (SnCl4) is first dissolved in propanol (or any other alcohol) forming a solution of tin compounds of type SnClx(OC3H7)y (typically stanic trichloride mono propoxide propyl alcoholate and tin dichloride di-propyl alcoholate):

Due to heat evolution, the solution is allowed to cool down to room temperature. Water-propanol mixture is then added to this for hydrolysis reaction. Another dilution with butanol may be followed to obtain desired SnO2 equivalent wt %.

In another method [76], SnCl4 is dissolved in deionized water (1 L) and the mixture is stirred for 24 h to obtain Sn(OH)4 precipitate:

This precipitate is separated using a centrifuge and washed several times using deionized water to remove the H+ and

Cl- ions until pH > 5. The precipitate is then peptized in deionized water with high pH (>11), which is obtained by adding appropriate amount of NH4OH. The resulting sol is suitable for thin-film formation.

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