NOVELTY - Etching of transparent conductive oxide layers placed on flexible polymer substrates or on hard substrate such as glass or a silicon wafer, involves applying etching pastes comprising at least one compound, which is a photo-acid generator, activating the etching composition by UV irradiating those areas, which shall be etched, removing the etching paste by rinsing off with water, and drying the treated surface.    USE - The method is useful for the etching of transparent conductive oxide layers placed on flexible polymer substrates or on hard substrate such as glass or a silicon wafer (claimed), where the conductive oxide layers are useful for producing solar cells and other semiconductor products.    ADVANTAGE - The method patterns transparent conductive oxide layers on flexible polymer substrates with reduced need for chemicals and a decreased total emission of chemicals into the environment, and high accuracy in an inexpensive, simple and rapid manner.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for an etching composition, comprising: at least one compound, which is a photo acid generator; an etching component comprising phosphoric acid (ortho-, meta- or pyro-), and its salt comprising diammonium hydrogen phosphate and ammonium dihydrogen phosphate, meta-phosphorus pentoxide, phosphonic acid, n-butyl phosphoric acid, di-n-butyl phosphoric acid, oligo- and polyphosphoric acids, phosphonic acid, phosphinic acid, phenylphosphinic acid, or phenylphosphonic acid, or comprising mono-, di- or triesters of the phosphoric acids, preferably monomethyl phosphate, di-n-butyl phosphate or tri-n-butyl phosphate; at least an organic solvent comprising acetone, polyhydric alcohols such as glycerin, polyethylene glycol, propylene glycol monomethylethylacetate, (2,2-butoxy(ethoxy))-ethyl acetate, ethers, preferably ethylene glycol monobutyl ether, triethylene glycol monomethyl ether or propylene glycol monomethyl ether, propylene carbonate, cyclopentanone, cyclohexanone, gamma -butyrolactone, N-methyl-2-pyrrolidone, ethyl lactate, and methoxypropyl acetate, preferably 1-methoxy-2-propyl acetate; water; optionally at least one thickener; and optionally additives.