The development of >28% efficient triple-junction space solar cells at Emcore Photovoltaics

Emcore Photovoltaics has been in volume production of high-efficiency multi-junction solar cells for spacecraft applications since 1999. Emcore´s current heritage product is the advanced triple-junction (ATJ) n/p InGaP/InGaAs/Ge solar cell. The ATJ cell exhibits a beginning-of-life (BOL) minimum average conversion efficiency of 27.5%, under air-mass zero (AM0) illumination conditions, making it the highest efficiency flight cell available in the market to date. The efficiencies of flight cells in a ship lot range from approximately 26.0% to 29.5%. A new version of the ATJ cell that is also in volume production at Emcore, incorporates a monolithically integrated p/n GaAs bypass diode. This cell is called the ATJM. Using the ATJM cell as the baseline platform, an optimized solar cell is being developed that is mechanically identical to the heritage ATJM cell, but exhibiting a minimum average efficiency of about 28.5%. The development lots of this 2nd generation ATJM exhibit typical BOL performance parameters of Voc of 2,650 mV, Jsc of 17.3 mA/cm/sup 2/, and fill factor of 84%, under illuminated AM0 conditions. In this paper, the manufacturing aspects of the ATJ & ATJM cells, as well as, the development aspects of the 2nd generation ATJM solar cells will be presented.