A comparison of quantum dot (QD) triple junction solar cells (TJSCs) under tensile strain are compared to those under compressive strain and baseline devices to examine the effects of strain induced by the QD layers. It is found that tensile strain leads to degradation of i-region material at values of -706 ppm. Irradiating with 1 MeV electrons triple junction solar cells with tensile strain exhibit a faster degradation in Ise of the QD samples and slower degradation in Voc but overall faster degradation in efficiency compared to baseline TJSCs, regardless of the magnitude of tensile strain. Compressively strain QD TJSCs have similar degradation in Isc and slower degradation in Voc compared to baseline TJSCs. From this study it is determined a strain of +400 ppm in the QD superlattice allows for the best performance pre-and post-irradiation for QD TJSCs based upon AMO IV and quantum efficiency.
Triple junction solar cells lattice matched to InP have the potential to exceed 50% efficiency under AM1.5 500x illumination with a bandgap stack of 1.74 11.1 10.7 eV. A top cell having 1.74 eV requires development of high-quality InAIAsSb, which currently has very little development effort reported. Preliminary deep-level transient spectroscopy results in p-type InAIAsSb indicate the presence of deep-levels 0.20 eV and 0.44 eV above the valence band with concentration _10 15 cm-3 • Experiments such as spectral response and dark IV analysis reveal poor solar cell metrics, which may be a direct consequence of the detected defects. The InAIAsSb deep-levels are comparedto the better-understood levels found in InAIAs, however, no evidence of a correlation is found.
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