Technical Insight
Tecstar's integrated diode protects solar cells in the dark (Opto News)
Tecstar has introduced a new multijunction solar cell that contains an integrated GaAs bypass diode designed to reduce damage to solar cells in space. The new device is based on Tecstar s commercially available triple junction GaInP2/GaAs/Ge solar cell a space qualified device with an efficiency of 26.5% and an end-of-life power of 86%. The three-junction devices are grown monolithically on Ge substrates, and the cells are connected using AlGaAs/GaInP2 p-n tunnel diode layers. Known as TEC3i, Tecstar s new design features a GaAs diode bypass layer grown as a mesa structure on the top AlInP2 window layer. The bypass diode protects the cell when the satellite is shadowed from the Sun by the Earth or by an antenna or panel. When in shadow, an unprotected device changes from a forward bias condition to reverse bias, which can cause damage. The monolithic bypass diode has been tested up to 100 000 extreme shadow cycles at a temperature of 120C. "The TEC3i is Tecstar s third generation monolithic three-junction design," said Frank Ho, VP of R&D at Tecstar. "We have grown an integrated bypass diode on top of the solar cell, which is connected to the Ge substrate to prevent the cell from burning out during a shadow cycle. The design offers advantages compared to discrete protection diodes. In particular, we can use masks to scale the diode size to accommodate customer requirements, depending on the solar conditions their cells will experience." According to Tecstar, the TEC3i is in volume production and can be supplied in the form of epiwafers, cells, cell assemblies or complete solar panels.
