Evolution and Recovery of Electrical Property of Reactive Sputtered Al‐Doped ZnO Transparent Electrode Exposed to Harsh Environment

Al‐doped ZnO (AZO) thin film is extensively studied as a promising alternative for Sn‐doped In2O3 (ITO) transparent electrode from the viewpoint of safety, environment, and material costs. However, most of AZO thin films are reported to degrade when exposed to high humidity. To find a key factor of durability, the electrical properties of AZO thin films after harsh conditions are characterized in this study. AZO thin films are prepared on glass substrates by reactive radiofrequency magnetron sputtering, followed by annealing at 400–550 °C in a hydrogen atmosphere. For harsh environment, a damp heat test is performed at 85 °C and 85% relative humidity, where the changes in both the carrier concentration and mobility are examined. It is found that the carrier concentration exhibits similar decreasing tendencies to conductivity degradation as a function of annealing temperature. This means that higher temperature contributes to the stability of carrier concentration, i.e., conductivity. Re‐annealing is also conducted for the AZO samples after the damp heat test, and the original conductivity is successfully recovered. This indicates that the degradation mechanism involves the chemical aspect rather than physical damage such as cracks, which cannot be recovered by annealing. Degradation of electrical properties is observed for aluminum‐doped zinc oxide (AZO) thin films exposed to a harsh environment. Recovery is achieved by reannealing the degraded AZO films in a hydrogen atmosphere at 400–550 °C. This indicates that the degradation mechanism involves chemical aspects such as diffusion of water molecules, which is reversible, rather than physical damage to the films.