A smart way to increase the efficiency of photovoltaic cells is to use the concept of photonic conversion (down conversion), which consists in converting high-energy photons into photons whose energy is within the maximum efficiency of the cells. This spectral modification is implemented by thin layers deposited on the front of the cells. The physical principle used for the spectral conversion is the photoluminescence. Among the most promising systems, we study, in the framework of this project, the transparent conducting oxides ZnO and SnO2. These host matrices are doped with different rare earths (Tb, Yb, Nd) to obtain the desired conversion properties. The deposition techniques used are sputtering and thermal evaporation for the physical routes and sol-gel and spray pyrolisis for the chemical routes. These techniques are compatible with the current manufacturing processes of the standard cell.