| Work Detail |
Spanish scientists have analyzed the impact of temperature and spectral conditions on III-V solar cells used in concentrator photovoltaic modules. They claim to have evaluated the behavior of the cells under unprecedented operating conditions.
A Spanish research group has studied the impact of temperature and spectral conditions on III-V solar cells operating under ultra-high concentration (UHC) conditions.
Gallium arsenide (GaAs) and other III-V materials - named after the groups of the periodic table to which they belong - are among the best known in terms of efficiency potential for solar cells. However, their high production cost has until now limited them to very specialized applications, such as powering satellites and drones. In these devices, low weight and high efficiency are more pressing concerns than the cost of the energy produced.
The researchers studied a triple junction solar cell based on gallium indium phosphide (GaInP), gallium indium arsenide (GaInAs) and germanium (Ge). “The measurements presented are unprecedented, since there are no previous publications that combine different spectral and controlled temperature experimental conditions in the UHC range, thus expanding the range of studies reported in works carried out at lower concentrations,” they highlighted.
To measure IV curves under different temperatures and power concentrations, the scientists built an experimental setup based on a multi-flash indoor solar simulator, which they claim allows operating temperatures of up to 85°C and irradiance concentration levels of up to 2,200 soles. Under these conditions, they produced several sets of IV curves based on 30 measurements per combination of temperature and concentration.
“To a first approximation, the curves show that both the open circuit current (Isc) and the short circuit voltage (Voc) increase with irradiance,” they discovered. “However, while Isc increases with temperature, Voc decreases. Thus, the parameters show a similar behavior in the UHC regime to that observed at lower concentrations.”
Regarding the short-circuit current, they identified an increasing linear dependence on temperature at constant irradiance levels and said that it depends on the irradiance. Considering the open circuit values ??as a function of the irradiances at different temperatures, they also found a “linear fit showing an increasing dependence on the irradiances and a good linear fit to the natural logarithm of the irradiance.” However, they have also found a negative linear dependence of the open circuit voltage on temperature at constant irradiance levels.
Furthermore, when analyzing the cell filling factor, the academics found a decreasing dependence as temperature and irradiance increased. “The data indicate a decreasing linear dependence of the efficiency with the logarithm of the irradiance,” they specified. “With respect to temperature, it shows a close linear relationship between cell efficiency and temperature at each irradiance level studied.”
The team also observed a strong correlation between relative variations in open-circuit voltage and efficiency with temperature. Furthermore, they performed an analysis of measurements of the response of cells to spectral variations in the UHC regime using the spectral matching ratio (SMR) factor, which is the ratio of the photogenerated currents of adjacent subcells under the same levels of irradiance.
“For SMR values ??< 1, the spectrum is red-shifted (with lower power density at short wavelengths compared to the standard), and less generation is obtained in the upper subcell,” the scientists stated. “In contrast, for SMR > 1, the middle subcell exhibits lower generation levels, although the total current is not equally affected by the same relative SMR deviations. In the opposite case, with SMR < 1, the contribution of the upper subcell is much smaller than that of the middle subcell in the case of SMR > 1”.
Their findings were presented in “ Multi-junction solar cell measurements at ultra-high irradiances for different temperatures and spectra,” published in Solar Energy Materials and Solar Cells . The group was made up of researchers from the University of Jaén and the Andaltec Technology Center. |
