Beneficial effects of hydrogen peroxide on growth, structural and electrical properties of sprayed fluorine-doped SnO2 films

Fluorine doped SnO2 thin films were spray deposited using three tin precursors, tin tetrachloride, dibutyl-tin-diacetate and butyl-tin-trichloride, adding small amounts of hydrogen peroxide (H2O2) to the source solutions. The molar ratio range [H2O2]/[Sn]=0 to 0.8 with respect to the tin precursor was investigated. At a given deposition temperature T-d, a net optimum was found close to [H2O2]/[Sn] = 0.5 for the deposition rate, the electrical properties and the crystalline quality. The effect of H2O2 addition was found to increase the growth rate, even at a temperature as low as 340 degrees C. The higher was the deposition temperature T-d, the larger was the increase. The deposition process of FTO films was optimized at T-d=420 degrees C. At this temperature, the most significant result with respect to solar cell applications was obtained with butyl-tin-trichloride as tin precursor and [H2O2]/[Sn]=0.6; carrier concentration : 4.5 x 10(20) cm(-3); mobility : 34 cm(2) V-1 s(-1); resistivity: 4.1 X 10(-4) Omega cm. It is concluded that the main effect of addition of hydrogen peroxide is to improve the film crystallization at a lower T-d than in the absence of H2O2, increasing the carrier mobility significantly and keeping a high deposition rate. (c) 2005 Elsevier B.V. All rights reserved.