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The investigated system is a combination of a Primary Optical Element (POE) consisting of an off-axis mirror and a receiver made of a Secondary Optical Element (SOE) on top of a Multi Junction Solar Cell (MJSC). This article investigates the mitigation of misalignment losses thanks to the SOE and the impact of POE temperature on misalignment and system efficiency. The optical and electrical efficiencies of two receivers with different SOEs are measured as a function of the POE temperature. The thermal behavior of the POE and the impact on the electrical efficiencies of the MJSC are estimated independently. [ABSTRACT FROM AUTHOR]

Multijunction solar cells (MJSC) use anti-reflective coatings (ARC) to minimize Fresnel reflection losses for a family of light incidence angles. These coatings adapt the refractive index of the cell to that of the surrounding medium. Patterns with sizes in the range of the light wavelength can be used to further reduce reflections through diffraction. Transparent nanopatterns with a gradual profile, called moth-eye nanostructures, can adapt the refractive index of the optical interfaces (often with n~1.5) used to encapsulate concentrator solar cells to that of the air (nair~1). Here we show the effect of a nanometric moth-eye ARC with a round motif deposited on commercial MJSC that achieves short-circuit current (ISC) gains greater than 2% at normal incidence and even higher in the case of tilted illumination. In this work, MJSC with different moth-eye ARC are characterized under quantum efficiency (QE) as well as under concentrated illumination I-V in order to assess their potential. Simulations based on coupled wave analysis (RCWA) are used to fit the experimental results with successful results. [ABSTRACT FROM AUTHOR]

Multijunction solar cells (MJSC) are usually developed to maximize efficiency under test conditions and not under real operation. This is the case of anti-reflective coatings (ARC), which are meant to minimize Fresnel reflection losses for a family of incident rays at room temperature. In order to understand and quantify the discrepancies between test and operation conditions, we have experimentally analyzed the spectral response of MJSC for a variety of incidence angles that are in practice received by a concentrator cell in high-concentration photovoltaic (HCPV) receiver designs. Moreover, we characterize this angular dependence as a function of temperature in order to reproduce real operation conditions. As the refractive index of the silicone is dependent on temperature, an optical mismatch is expected. Regarding other characterization techniques, a method called Relative EL Homogeneity Analysis (RELHA) is applied to processed wafers prior to dicing, allowing to diagnose the wafer crystalline homogeneity for each junction. Finally, current (I)-voltage (V) characterization under strongly unbalanced light spectra has also been carried out for a number of low-level irradiances, providing insight on each junction shunt resistance and corresponding radiative coupling. [ABSTRACT FROM AUTHOR]