Substrate and back contact effects in CIGS devices on steel foil

In comparison to CIGS-based photovoltaic devices deposited onto soda-lime glass substrates, the observed efficiency limitations of similar devices prepared on flexible metal substrates have been attributed to factors that include: (a) lack of sodium out-diffusion from the substrate; (b) impurity out-diffusion from the substrate, and (c) substrate roughness. While intentional Na incorporation via deposition of a Na-containing precursor has previously been studied extensively in the literature, this investigation focuses on the latter two issues. If thin metal back contact layers are employed, these two factors are more closely linked than for thick back contact layers. The effects of various metal surface-finishing techniques on substrate roughness, impurity out-diffusion, and subsequent device performance are examined.