Current Photovoltaic Research ISSN:2288-3274(Print) 2508-125X(Online)

Two-step processes for preparing Cu(In,Ga)Se₂ absorber layers consist of precursor layer formation and subsequent annealing in a Se-containing atmosphere. Among the various deposition methods for precursor layer, the nonvacuum (wet) processes have been spotlighted as alternatives to vacuum-based methods due to their potential to realize low-cost, scalable PV devices. However, due to its porous nature, the precursor layer deposited on Mo substrate by nonvacuum methods often suffers from thick MoSe₂ formation during selenization under a high Se vapor pressure. On the contrary, selenization under a low Se pressure to avoid MoSe₂ formation typically leads to low crystal quality of absorber films. Although TiN has been reported as a diffusion barrier against Se¹⁾, the additional sputtering to deposit TiN layer may induce the complexity of fabrication process and nullify the advantages of nonvacuum deposition of absorber film. In this work, Mo oxide layers via thermal oxidation of Mo substrate have been explored as an alternative diffusion barrier. The morphology and phase evolution was examined as a function of oxidation temperature. The resulting Mo/Mo oxides double layers were employed as a back contact electrode for CuInSe2 solar cells and were found to effectively suppress the formation of MoSe2 layer.