Analyzing UV/Vis/NIR Spectra—Part II: Correct and Efficient Parameter Extraction

Exact optical analysis of transparent conducting oxide (TCO) and absorber layers are necessary to optimize adequate materials for thin-film solar cell applications. A nonnumerical theoretical concept has been developed to extract approximation-free optical and electrical data from ultraviolet/visible/near-infrared (UV/Vis/NIR) spectra. Special focus has been set on double-layer systems, as thin films upon substrates. Complex parameter evaluation is possible. Sputtered TCO and absorber thin films - aluminum-doped zinc-oxide and tin-sulphide - have been analyzed with respect to process-temperature T. Results were compared with those of the well-known Keradec/Swanepoel model. The necessity of taking both spectra - transmission and reflection spectra - into account has been shown. Results have been discussed with structural properties of the thin films with the help of X-ray diffraction measurements. A noncontact, optical conductivity measurement possibility by use of UV/Vis/NIR spectroscopy has been introduced. Optically measured conductivities σ_L were compared with those measured electrically with a four-tip measurement system.