High concentration testing and performance of multijunction solar cells

The use of the appropriate characterization tools along with the use of single cell assemblies that are robust, are necessary for proper evaluation of device performance and stability tests for GaInP₂/GaAs/Ge triple junction (3J) concentrator solar cells. Certain discrepancies exist between the photovoltaic (PV) values from continuous outdoor illumination measurements at high concentration levels and those from the High Intensity Pulse Solar Simulator (HIPSS) measurements, which are addressed. The series resistance inferred from the current-voltage (IV) curve, however, is similar from both measurement techniques. Outdoor tests of concentrator cells yielded efficiencies near 29% (31% from HIPSS) for an average concentration of 432 suns. Both types of measurements revealed that the fill factor (FF) limited the performance of the cell at high concentrations due to the role of the series resistance. The formation of heat from the nonuniformity in the Fresnel optics also limited the device performance. Before the cell stability can be evaluated, cells are first screened for defects from the 1-sun, indoor, IV measurements. Then, the good cells are incorporated into small assemblies for further test by forward bias injection (FBI). The stability outcome of the FBI determines whether or not the cell can be used for outdoors tests. Outdoor IV measurements are then conducted. Stability test results showed that no degradation occurs in the 1-sun IV data before and after light soak of the concentrator assemblies.