Effect of Low-Intensity-Low-Temperature and High Radiation conditions on Flexible Cu(In,Ga)Se2 Solar Cells  
Collin R. Brown1, Hadi Afshari1, Vincent R. Whiteside1, Dmitry Poplavskyy2, Khalid Hossain3, Mangal S. Dhoubhadel3, Ian R. Sellers1
1Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK, United States
/2MiaSolé Hi-Tech Corp., Santa Clara, CA, United States
/3Amethyst Research Inc., Ardmore, OK, United States

Cu(In, Ga)Se2 (CIGS) solar cells have been studied for space applications for a number of years due to their radiation tolerance and low cost. Most early work has studied CIGS on soda lime glass, which is too bulky for space applications, and would not allow for the complex folding arrays that have been proposed for future deep space missions. Here, commercially available flexible CIGS solar cells are investigated under conditions consistent with those around the outer planets. Performance under these low temperature low intensity (LILT) conditions is critical to study, as these conditions can reveal issues not present under normal operation. Current density-voltage (J-V) and external quantum efficiency (EQE) measurements under different temperature, illumination, and bias conditions are performed to investigate the environmental effects of these deep space conditions. Of particular interest at low temperature is the behavior of the well-known VCu-VSe metastable defect, and its potential role in device performance under LILT conditions. Here, evidence of a photo-activated barrier is observed, which is attributed to the same defect center, although its effect on power generation at LILT conditions appears to be minimal. Increased Voc at low temperature leads to increased performance. Additionally, proton irradiation with high fluence levels is investigated to emulate certain conditions near Jupiter. Although degradation is observed, self-healing behavior under annealing conditions is also evident. These data show that in systems where low cost, weight and flexibility are paramount, flexible CIGS may be a promising alternative for low cost LILT missions.