Recent Progress of Multi-Junction Solar Cell Development for CPV Applications at AZUR SPACE
The next generation concentrator photovoltaic (CPV) solar cell from AZUR SPACE will be a five-junction upright metamorphic (5J-UMM) cell that is currently under development. The main design criteria for this 5J-UMM cell is to allow for the highest possible system performance instead of the highest cell efficiency under concentrating standard test conditions (CSTC) while retaining a low e/W price on system level. Our new 4J-UMM space solar cell has been used as the basis for the 5J-CPV cell. In subsequent development steps, a fifth subcell was added to the 4J-UMM structure and the band gap for each subcell was optimized for the terrestrial spectrum and for operating conditions of the system of 90°C. Furthermore, the tunnel diodes and the material quality of each subcell has been optimized. With this approach a 5.2 x 5.2 mm² 5J cell with 41% efficiency at 589 suns (25°C, AM1.5d) has been achieved. We expect the in-system performance of the current 5J-UMM cell already to be better compared to the existing triple junction solar cell product 3C44. Due to a severe current-mismatch in the current 5J-cell an immediate improvement potential of 8% in short circuit current density (Jsc) is available for a properly current-matched cell. Such an increased Jsc results in devices with efficiencies > 44% at CSTC.