Studying the Impact of Impurities on the Performance of Cadmium‐Free all Sputtered CIGS Solar Cells Using Titanium–Tungsten Barrier

Midsummer AB specializes in producing flexible, lightweight, cadmium‐free, all‐sputtered Cu(In, Ga)Se 2 (CIGS) modules on steel substrates. This study investigates the role of a titanium/tungsten (TiW) barrier layer, placed between the steel substrate and the back contact, in controlling the diffusion of three major impurities—iron (Fe), chromium (Cr), and nickel (Ni)—which are believed to be detrimental to CIGS devices. For a device with a 64 nm barrier layer, an efficiency of 14% is obtained, limited by a reduced fill factor (FF) and low open‐circuit voltage ( V OC ). Increasing the thickness of the barrier layer to 128 nm leads to improvements in both V OC and FF, yielding an efficiency of 16%. This finding is supported by secondary ion mass spectrometry measurements, which show lower impurity levels for thicker barriers. The results indicate that impurity diffusion into the CIGS layer during deposition significantly affects device performance, but this can be mitigated using TiW barrier layers. Glow discharge optical emission spectroscopy is employed to examine the in‐depth compositional profile of the CIGS layer. Additionally, a solar cell capacitance simulator (SCAPS‐1D) is used to assess the impact of impurities on performance and compare the results with experimental data.