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The effects of Na and RbF alkali treatment on the metastability behavior of CdS/Cu(In,Ga)Se2 solar cells are investigated with stress factors of heat, junction bias, and illumination. Four device types with and without Na or RbF treatments are subjected to heat‐ and light‐soaking under open‐ and short‐circuit (OC, SC) junction bias. Low‐Na devices show a higher bandgap due to increased minimum Ga content, higher recombination current, and lower open‐circuit voltage (VOC). Devices with RbF post‐deposition treatment (PDT) show an improvement in net doping density ≈1016 cm−3, VOC, and efficiency. Heat‐ and light‐soaking under OC junction bias provokes an increase in net carrier concentration and VOC irrespective of the alkali treatments. After SC stress, a decrease in VOC and net carrier concentration is observed, which can be stabilized by RbF‐PDT. An increase in Na and oxygen concentration in CIGS is observed for baseline and low‐Na devices, respectively, after OC stress. The oxygen concentration in CdS decreases after heat‐ and light‐soaking for devices without RbF‐PDT, whereas it remains unchanged for devices with RbF‐PDT. The atomic concentration profiles in CIGS significantly stabilize as a function of stress with the addition of RbF‐PDT. [ABSTRACT FROM AUTHOR]