Fluoride additive in epoxide-initiated sol–gel synthesis enables thin-film applications of SnO2 aerogels

Abstract

Aerogels of SnO₂ were synthesized by an epoxide-initiated sol–gel method. Using ammonium fluoride in the precursor solution allowed for tunability of the aerogel morphology while no change in the conductivity was measured. In particular, aerogel shrinkage was decreased dramatically by the addition of the fluoride precursor. Unfluorinated aerogels showed severe shrinkage of 43% volume change upon supercritical drying compared to the original alcogel volume. Fluorinated samples exhibited a much less pronounced shrinkage at 7%. Multiple characterization methods converged to reveal the mechanism by which fluoride enables the morphological tunability. These findings enable the casting of SnO₂ aerogels as thin films (which in the absence of fluoride these crack and delaminate due to shrinkage), opening potential uses in many optoelectronic devices including solar cells.