<p>An inkjet ink comprises phosphoric acid; one or more solvents for the phosphoric acid, preferably ethyl lactate and water; and one or more aprotic organic sulfoxides, preferably dimethyl sulfoxide (DMSO) or dimethyl sulfone (SMSO2). The inks do not leave a carbon residue on heating and so are suited to use in etching and/or doping silicon wafers, e.g. in the production of crystalline silicon solar cells.</p>
