Qualification testing of the ZTJ GaInP2/GaInAs/Ge solar cell to the AIAA S-111 standard

We report the results to date of qualification testing of Emcore's sixth generation III-V multi-junction solar cell - the ZTJ GaInP
₂
/Ga(In)As/Ge cell. The ZTJ cell is currently undergoing space qualification per the requirements of the American Institute of Aeronautics and Astronautics (AIAA) S-111-2005 standard. The S-111 document consists of a comprehensive set of qualification tests, which include front/backside weld testing, electrical characterization, humidity exposure, radiation response, bend/mechanical tests, electrostatic discharge sensitivity, DIV, capacitance, and coupon level (both illuminated and dark) thermal cycling. With the exception of energetic charged particle irradiation and temperature-dependent LIV, all of the qualification tests are performed at Emcore. The coupon level thermal cycling testing known as ?combined effects? testing is designed to simulate the conditions the coupon will experience in geosynchronous Earth orbit (GEO). Emcore is in the process of establishing a combined effects test system to qualify the ZTJ as well as all future space solar cells to the S-111 standard. An overview of the design of the combined effects facility is presented, as well as test results. Initial data acquired from the combined effects chamber show 5.7% light uniformity over the illuminated panel area, and that the chamber meets the GEO temperature cycling requirements of -180?C to +80?C. The ZTJ cell exhibits a beginning of life (BOL) maximum power point efficiency of 29.5% (135.5 mW/cm2) under simulated AM0 illumination at 28?C. The ZTJ cell design incorporates features that have resulted in improved efficiency by 1% absolute over the previous generation BTJ cell while maintaining equivalent radiation hardness (84% remaining power) to 1 MeV electrons. Tests for temperature-dependent LIV, DIV, humidity, capacitance, ESD, and bend have been performed to date. Temperature coefficients for the ZTJ cell are: Voc = -6mV/?C, Jsc = 1.14E-2 mA/cm
²
/?C, FF = -4.33E-2/?C, Eff = -5.73E-2/?C, and max power = -0.312 mW/?C. The ZTJ cell is quite resistant to RB breakdown and human body model (HBM) ESD events, exhibiting an average RB breakdown voltage of -33.5V, and no change in DIV behavior following +/- 16 kV ESD pulses. Frequency-dependent capacitance measurements exhibit good agreement with theoretical models. In addition, negligible degradation is observed after 60 days of 45?C/95% humidity exposure, with a power remaining factor of 99.5%. Bend tests show that no fracture occurs until a bending diameter of 6".