This work presents an experimental analysis and analytical modeling of cell to module losses for passivated emitter and rear cells (PERC), which enables to build a PERC solar module with a record efficiency of 20.2%. Further, it examines the ultraviolet radiation hardness of solar modules employing crystalline silicon (c-Si) solar cells featuring dielectric passivation layers.Passivated emitter and rear cells are on the transition to mass production and expected to become the dominating c-Si solar cell technology in terms of market share in the next few years. Thus, it is of major importance to implement these high efficiency PERC into high efficiency solar modules. When transferring solar cells into a solar module additional recombination, optical, and resistive losses reduce the power of the solar module compared to the power of the solar cell, termed cell to module losses. In this work we study the individual recombination, optical, and resistive characteristics of various cell and module test samples. Based on our experimental results we develop an analytical model that allows to simulate the cell to module losses and reproduces the measurement results of test modules within the measurement uncertainty. We show that a reduction of the cell to module losses requires an adaptation of both, the solar cell as well as the solar module components. We employ the analytical model to improve the cell's front metalization, cell interconnection, light harvesting and cell spacing to reduce the cell to module losses for passivated emitter and rear cells and build an industrial like 60-cell sized solar module with a record power conversion efficiency of 20.2%.Besides the efficiency, the long-term reliability of solar modules is crucial and a performance degradation of new promising technologies can impair their importance for the industry. The application of new metalization pastes that enable to contact lowly doped emitters, increases the spectral response of a PERC in the UV wavelength range. This requires the application of new encapsulation materials with enhanced UV transmittance for PERC solar modules. We report on the UV radiation hardness of solar modules featuring PERC with various silicone nitride passivation layers and employing different encapsulation polymers. Our results reveal that employing polymers with increased UV transparency results in a solar module power loss of 14%. We show that the degradation in module power is due to a reduction of the module's open circuit voltage. This loss is related to an increased charge carrier recombination in the cell, which we ascribe to a degradation of the amorphous silicon nitride (SiN) surface passivation. We develop a novel analytical model to describe the effect of high energetic photons on the solar module performance with a critical energy to deteriorate the surface passivation.