Photovoltaic device (1a, 1b, 1c, 1d, 1e, 1f, 1g, 1 h, 1g) with a hetero-junction, said photovoltaic device having a front side for an incidence of light and comprising - a crystalline semiconductor body, - a front passivation layer formed on a front surface of the crystalline semiconductor body, - an emitter or a front surface field layer formed on the front passivation layer, - a front-sided transparent conductive material stack, and - a front grid metallization, wherein the front-sided transparent conductive material stack is a stack of at least two transparent conductive components having different compositions, wherein the front-sided transparent conductive material stack comprises - a front-sided first transparent conductive layer consisting of a first base material with a first doping and having a non-stoichiometric composition with a first deviation from stoichiometry, wherein the first base material is chosen from the group of materials including indium oxide, zinc oxide, tin oxide, and cadmium oxide, and - a front-sided second transparent conductive layer or structure (6, 6a, 6b) consisting of the first base material or a second base material, said first or second base material having the first doping or a second doping being different from the first doping and having a non-stoichiometric composition, wherein the composition of the second base material is different from the composition of the first base material characterized in that the composition of the first base material of said front-sided second transparent conductive layer or structure (6, 6a, 6b) has a second deviation from stoichiometry being different from the first deviation from stoichiometry, respectively, and wherein the average carrier concentration of the whole front-sided transparent conductive material stack is between 1 x 10 20 cm -3 and 2 x 10 20 cm -3; the refractive indices (n) of the front-sided first transparent conductive layer and of the front-sided second transparent conductive layer or structure (6, 6a, 6b) are in the same range, wherein n > 2 at a wavelength of about 550 nm; and the carrier mobility in the font-sided first transparent conductive layer is higher than the carrier mobility in the front-sided second transparent conductive layer or structure (6, 6a, 6b) if the layers/structure (5; 6, 6a, 6b) have a comparable thickness. - a crystalline semiconductor body, - a front passivation layer formed on a front surface of the crystalline semiconductor body, - an emitter or a front surface field layer formed on the front passivation layer, - a front-sided transparent conductive material stack, and - a front grid metallization, wherein the front-sided transparent conductive material stack is a stack of at least two transparent conductive components having different compositions, wherein the front-sided transparent conductive material stack comprises - a front-sided first transparent conductive layer consisting of a first base material with a first doping and having a non-stoichiometric composition with a first deviation from stoichiometry, wherein the first base material is chosen from the group of materials including indium oxide, zinc oxide, tin oxide, and cadmium oxide, and - a front-sided second transparent conductive layer or structure (6, 6a, 6b) consisting of the first base material or a second base material, said first or second base material having the first doping or a second doping being different from the first doping and having a non-stoichiometric composition, wherein the composition of the second base material is different from the composition of the first base material characterized in that the composition of the first base material of said front-sided second transparent conductive layer or structure (6, 6a, 6b) has a second deviation from stoichiometry being different from the first deviation from stoichiometry, respectively,