A Spanish research team has explored how temperature and light spectrum variations impact III-V solar cells under ultra-high concentration (UHC) conditions.
These solar cells, made from materials like Gallium Arsenide (GaAs) and other III-V elements, are known for their high efficiency but are expensive, limiting their use to specific applications like powering satellites and drones where efficiency and low weight are vital despite the high cost.
The team focused on a triple-junction solar cell comprising gallium indium phosphide (GaInP), gallium indium arsenide (GaInAs), and Germanium (Ge). They highlighted their unique approach, combining various spectral and temperature conditions in their experiments, which hasn't been done before at these high concentration levels.
Using a sophisticated indoor solar simulator, they could test the cells at temperatures up to 85°C and irradiance levels as high as 2,200 suns. Their tests, involving 30 measurements for each temperature and concentration combination, revealed that both the open-circuit current (Isc) and short-circuit voltage (Voc) increase with more light but react differently to temperature changes. While Isc rises with temperature, Voc falls, showing similar behavior to cells at lower concentrations.
The research further indicated a linear dependency of the short-circuit current on the temperature at constant light levels and a similar increasing trend of the open-circuit values with light intensity. However, the open-circuit voltage showed a negative linear response to temperature at constant light levels.
Additionally, the cell's efficiency and fill factor decrease with higher temperatures and light intensities, showing a strong correlation between open-circuit voltage, efficiency, and temperature. They also examined the cell's response to different light spectra using the spectral matching ratio (SMR), which compares the photogenerated currents of adjacent subcells under the same light conditions. They observed that the spectrum's shift (red or otherwise) affects the generation levels in different subcells.
These insights are documented in their study, “Multi-junction solar cell measurements at ultra-high irradiances for different temperatures and spectra,” published in Solar Energy Materials and Solar Cells.
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