Effect of Processing on the Electrical Properties of Spray-Deposited SnO2:F Thin Films

Highly transparent SnO₂:F thin films were produced by the Spray Pyrolysis (SP) technique to be used as forcontacts in the home made CdS/CdTe solar cells. Films of thickness 100-200 nm were prepared at substrate temperatures in the range 380-480°C. To improve the electrical properties of the films, annealing in nitrogen atmosphere at 400°C and etching by HNO₃ were tried. The resistivity of the films was calculated from the I-V plots which are all linear. It had significantly decreased after annealing, but slightly decreased after HNO3-etching alone. The improvement in the electrical properties was accompanied by an improvement in the X-Ray Diffraction (XRD) spectra and an increase in the grain size as shown by the scanning electron microscope (SEM) images. The annealing period needed to obtain the lowest resistivity was longer for films prepared at lower substrate temperatures.