Using HF rather than NH4F as doping source for spray-deposited SnO2:F thin films

Fluorine doped tin oxide SnO₂:F thin films were prepared by the spray pyrolysis (SP) technique on glass substrates by using SnCl₂·2H₂O as a precursor and NH4F and HF as doping compounds. A comparison between the properties of the films obtained by using the two doping compounds was performed by using I–V characteristics in the dark at room temperature, AC measurements, and transmittance. It is found that the films prepared by using HF have smaller resistivity, lower impedance and they are less capacitive than films prepared by using NH₄F. In addition, these films have higher transmittance, higher optical bandgap energy and narrower Urbach tail width. These results are interesting for the use of SnO₂:F as forecontact in CdS/CdTe solar cells.