III–V multijunction solar cells for ultra-high concentration photovoltaics

In this paper, the benefits of the ultra high concentration (¿ 1000 suns) are shown in terms of cost reduction and efficiency increase. Accordingly, the strategy followed at IES-UPM for more than 15 years is the development of III-V solar cells suitable for operation at 1000 suns or more. Recently, we have developed and manufactured a GaInP/GaAs dual-junction cell which results in an efficiency (measured at the Calibration Laboratory, CalLab, of Fraunhofer Institute in Freiburg) of 32.6% for a concentration range going from 499 to 1026 suns. This efficiency is the world record efficiency for a dual-junction solar cell. Besides, the efficiency is still as high as 31% at 3000 suns. The theoretical optimization of this solar cell (based on an accurate modelling) shows a potential efficiency over 36% at 1000 suns. We have extended this strategy to lattice-matched GaInP/Ga(In)As/Ge triple junction solar cells. First manufactured cells exhibit an efficiency of 31.5% at 1000 suns. The theoretical optimization of this cells show that an efficiency over 43% at 1000 suns is achievable. A roadmap has been established in order to reach this value.