Mathias Gruber

• Photovoltaic cells based on organic semiconductors promise to provide low cost, flexible, lightweight and even semitransparent solar power for various applications. However, a cost effective fabrication of organic solar modules can only be achieved when large-scale roll-to roll (R2R) processing techniques as well as low-cost substrates and materials are used. As the transparent electrode is a major cost driver for R2R-fabricated organic photovoltaics (OPVs), this work presents the usage of a commercially available metal mesh film as cost effective transparent electrode for indium-tin-oxide (ITO)-free organic solar cells. For this purpose, four different metal mesh based organic solar cell architectures were optimized and studied in detail, leading to the identification of two layer stacks matching the requirements for R2R production. Furthermore, a simple model for the optimization of the metal mesh geometry and the corresponding solar cell layer stack is demonstrated, compared to experimental data and used to achieve optimum device performance while ensuring R2R processing compatibility. As an alternative approach, the Light-Bias Light-Beam-Induced-Current (LB-LBIC) technique, a new variant of the traditional LBIC measurement, which allows the visualization of lateral charge-extraction in metal mesh based solar cells is shown. An analytical model to explain the LB-LBIC measurement results is developed and used to verify the metal mesh optimization results. In the final part of this work, the extension of the photoactive area ("‘photoactive area spreading"’) of solar cells, which is caused by unstructured layers, is introduced and a model to describe the effect is presented. The model is used to extract spreading-free photocurrents from measured solar cell current-voltage data and is shown to provide more accurate results compared to conventional shadow-masking.