Strain Effects on Radiation Tolerance of Triple-Junction Solar Cells With InAs Quantum Dots in the GaAs Junction

A comparison of quantum dot (QD) triple-junction solar cells (TJSCs) with the QD superlattice under tensile strain are compared with those under compressive strain and baseline devices to examine the effects of strain induced by the InAs QD layers in the middle junction. Theoretical results show samples with tensile-strained InAs QDs have lower defect formation energy while compressive-strained QDs have the greatest. Experimentally, it is found that tensile strain leads to degradation of i-region material at values of -706 ppm. Irradiating with 1-MeV electrons, TJSCs with tensile strain exhibit a faster degradation in I_sc of the QD samples and slower degradation in V_oc but overall faster degradation in efficiency compared with baseline TJSCs, regardless of the magnitude of tensile strain. Compressively strained QD TJSCs have similar degradation in I_sc and slower degradation in V_oc compared with baseline TJSCs. From this study, it is determined that a slightly compressive strain in the QD superlattice allows for the best performance pre- and postirradiation for QD TJSCs based upon AM0 IV and quantum efficiency measurements and analysis. Fabricating devices with improvements determined from samples with varying strain leads to QD TJSCs with better radiation tolerance in terms of power output for 5, 10, 15, and 20 layers of QDs.