Study on the performance of titanium film as a diffusion barrier layer for CIGS solar-cell application on stainless-steel substrates

In this paper, pure titanium (Ti) thin films deposited by radio frequency sputtering were used as a diffusion barrier layer in a flexible copper indium gallium selenium (CIGS) solar cell on a stainless-steel foil and characterized by X-ray diffraction, scanning electron microscopy and second ion mass spectroscopy measurement methods. The influences of the magnetron sputtering pressure on the surface morphology and preferred crystal orientation of Ti films are discussed. It was found that the Ti film showed a (001) preferred orientation and smooth surface topography at lower deposition pressure, while (002) preferred orientation and relatively rough surface topography at higher deposition pressure. In addition, Ti films made with different process pressures were deposited as the barriers and the second ion mass spectroscopy results indicated that a Ti film with the thickness of 200 nm was able to effectively block Fe and Cr diffusion from the stainless-steel foil into the CIGS absorber across the molybdenum back contact. The Ti barrier significantly improved the conversion efficiency of the CIGS solar cell.