Investigating the Role of Ag and Ga Content in the Stability of Wide‐Gap (Ag,Cu)(In,Ga)Se2 Thin‐Film Solar Cells

Abstract

The stability of thin‐film solar cells spanning a wide range of compositions within the (Ag,Cu)(In,Ga)Se2 material system is evaluated over time, after dry‐heat annealing and after light soaking, and the role of Ag and Ga content is explored. Ag‐free CuInSe2 is relatively stable to annealing and storage, while Cu(In,Ga)Se2 suffers a degradation of fill factor and carrier collection. High‐Ga (Ag,Cu)(In,Ga)Se2 suffers degradation of carrier collection after prolonged annealing, reducing the short‐circuit current by ≈12%. Ga‐free (Ag,Cu)InSe2 loses up to a third of open‐circuit voltage and a quarter of fill factor after all treatments are applied. All samples suffer voltage losses after light soaking, with the Ga‐free devices losing up to 50 mV and those containing Ga losing up to 90 mV. Ag incorporation leads to a significant reduction in doping, and a significant increase in the response of doping to treatments, with the depletion width of (Ag,Cu)(In,Ga)Se2 samples expanding from ≈0.1 μm as‐grown to beyond 1.0 μm after all treatments, compared to the Cu(In,Ga)Se2 sample variation of ≈0.1–0.3 μm. Connections between Ag content, doping instability, and performance degradation are discussed.