Photovoltaic device and method of manufacturing same

Hetero-junction solar cell with front side TCO stack comprising a front-sided first transparent conductive layer (5) of a first base material with a first doping and a first non-stoichiometric composition, wherein the first base material is chosen from indium oxide, zinc oxide, tin oxide, and cadmium oxide; and a front-sided second transparent conductive layer (6, 6a, 6b) or structure of the first base material or a second base material, having the first or second doping and a second non-stoichiometric composition. 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 first and second layers 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 if the layers/structure have a comparable thickness.