Highly transparent, low-resistance SnO2:F films suitable as a substrate material for thin film CdS/CdTe solar cells have been developed on 10 X 10 cm glass substrates by an ultrasonic spray pyrolysis (pyrosol) technique using dimethyltin dichloride (DMTDC) as a tin source. DMTDC, NH4F and HF, all dissolved in water, served as the source solution. An ultrasonic vibrator operated at 1.5 MHz produced a fine spray of the source solution. It was transported, using air as a carrier gas, to moving glass plates in a belt furnace maintained at 530 degrees C. A very high growth rate of nearly 100 Angstrom/s was realized in this process with good homogenity, high transparency, and low resistivity. Films with a sheet resistance of less than 10 Omega/square have been routinely prepared and their preparation technology has been well established. A proper nozzle design and exhaust system to remove the spent gases determines the technology of obtaining spot and cloud free homogeneous films in the belt furnace. A film of 5000 A thickness exhibited the lowest electrical resistivity, of 3.9 x 10(-4) Omega cm, a mobility value of 38 cm(2) V-1 s(-1), and a donor concentration of 4.16 x 10(20) cm(-3) Films of 5000-6000 Angstrom thickness having an average transmittance of nearly 85% in the visible range and a sheer resistance of around 8 Omega/square were used as transparent conducting oxide film substrates to fabricate thin film CdS/CdTe solar cells. A solar energy conversion efficiency of over 14% was achieved.