Development of Quality FTO Films by Spray Pyrolysis for Dye-Sensitized Solar Cell

Abstract

Fluorine-doped tin oxide (FTO) thin films were prepared, at different substrate temperatures, using dilute precursor solutions of di(n-butyl)tin(iv) diacetate (0.1 M DBTDA) by varying the F⁻ concentration in the solution. Morphology of SEM image revels that grain size and its distribution are affected by the substrate temperature. At the lowest temperature (400°C) the grain size become the smallest and at the highest temperature grain size become larger while at moderate temperature it has a large distribution of grain sizes. XPS calculation reveals that fluorine doping will decrease when substrate temperature is increased. Carrier concentration measured from hall coefficient analysis is found to be varying with the amount of fluorine doping as well as with the surface area of the film. Mobility becomes the lowest for the lowest grained FTO and it is the highest for the largest grained FTO. The best film, has large distribution of grain sizes (50–400 nm), gives an electronic conductivity of 31.85 × 10² Ω⁻¹ cm⁻¹, sheet resistance of 4.4 Ω/square with over 80% transmittance (400–800 nm). Optimum conditions of the best FTO film were 0.1 M DBTDA, 0.3 M ammonium fluoride, in a mixture of propan-2-ol and water, at 470°C substrate temperature. Dye-sensitized solar cells were fabricated using both the FTO films thus prepared and with the commercial FTO film. The best efficiency of 6.48% was observed for the cell fabricated from the best FTO films prepared at 470°C whereas the cells fabricated from the commercial FTO shows 5.30% light-to-electricity conversion efficiency (Illumination–A.M 1.5, Cell active area–1 cm², MPN based electrolyte–I⁻/I₃⁻).