Color rendering of semi-transparent fully sputtered germanium solar cells: a sensitivity study

Semi-transparent photovoltaics can replace conventional solar control glass, particularly when fabricated by high-throughput sputter deposition. We demonstrate that a fully sputtered transparent layer stack with realistic solar cell properties and with an ultrathin germanium absorber provides nearly color-neutral transmission and a suitable reflectance spectrum. The optical constants of all layers are used to build an optical model of the stack, enabling analysis of color rendering, angular dependence, and overall appearance. A sample deposited with model-optimized layer thicknesses confirms the predicted color neutrality. A subsequent sensitivity analysis reveals that color stability is dominated by relative thickness variations of the AZO layers, while deviations in other layers play a secondary role. These results highlight the suitability of the proposed architecture for facade-integrated, visually unobtrusive solar power generation.