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Light management in solar cells with planar structures and scattering media

2020
Koç, Mehmet
Photovoltaics is a prime interest for not only developed but also developing countries considering its historically-low efficiency/cost ratio. Further development of solar cells necessitates the maximum utilization of available light, which has to be done by taking the multi-physics nature of the solar cells and the fabrication constraints to maintain its competitive price into account. In this thesis, we explore light management strategies to improve the overall performances of various solar cells. First, light management is exploited to eliminate the reflection, and at the same time to increase the trapping of the non-reflected light within the active layer in the thin-film solar cells. Using optical simulation methods, transfer matrix method (TMM), finite-difference time-domain approach (FDTD), and ray-tracing, as well as analytical approaches, material independent optical optimization guidelines are provided for achieving higher optical absorption under ideal and practical conditions. Simple and effective empirical algorithms are developed to replace simulations. Developed algorithms are applied to various thin-film solar cell technologies; particularly, perovskite, organic, and CdTe solar cells. Besides, optoelectronic effects of transparent conductive oxides in thin-film solar cells are discussed. Using the simultaneous optimization of optoelectronic properties of cell geometries, we develop a roadmap for the perovskite solar cells that can increase their efficiency and at the same time decrease the fabrication costs. Secondly, we have presented a low-cost rear reflector material for silicon solar cells to eliminate the metal parasitic absorption. Using a combination of three different optical simulations methods (TMM, Ray Tracing, and FDTD), optical interaction mechanisms are quantized. Lastly, using a combination of thin-film and silicon solar cell technologies, we provide a detailed investigation of CdZnTe-Si tandem solar cells. We present theoretical limits of CdZnTe-Si tandem solar cells using a combined optical and electrical simulations environment. We investigate the effect of the top cell absorber bandgap on the optimum optical and electrical trends. Light management strategies provided in this thesis can be beneficial for researchers developing various types of solar cells, not necessarily skilled in optics.