Characterization of a molybdenum electrode deposited by sputtering and its effect on Cu(In,Ga)Se-2 solar cells

Molybdenum films were deposited on soda-lime glass substrates by using DC magnetron sputtering. Their structural and morphological properties and their electrical resistivities were analyzed with respect to the working gas (Ar) pressure. The electrical resistivity of the Mo films monotonically increased as the gas pressure was increased. The films showed a (110) preferred orientation, regardless of the working gas pressure. The surface morphology of the films changed from an elongated grain structure at lower working pressures to a porous nodular shape at higher pressures. The surface roughness of the films increased with the working gas pressure. Secondary ion mass spectrometry data showed that Na diffusion from the soda lime glass substrate through the Mo back contact was high, for the film sputtered at 5 mTorr. Cu(InGa)Se2 solar cells fabricated on Mo films sputtered at 5 mTorr showed the best conversion efficiencies.