Influence of the atmospheric species water, oxygen, nitrogen and carbon dioxide on the degradation of aluminum doped zinc oxide layers

• ZnO:Al films were exposed to H2O purged with CO2, O2, N2 and air and to gases.
• ZnO:Al films are almost stable H2O purged with O2 and N2 and individual gases.
• ZnO:Al films dissolve in H2O purged with CO2, but degrade quickly in air purged H2O.
• Degradation results mainly in mobility decrease as well as optical changes.
• Possible degradation products are Zn(OH)2, Zn5(OH)6(CO3)2 and species with Cl or S.

Aluminum doped zinc oxide (ZnO:Al) layers were exposed to the atmospheric gases carbon dioxide (CO2), oxygen (O2), nitrogen (N2) and air as well as liquid H2O purged with these gases, in order to investigate the chemical degradation behavior of these layers. The samples were analyzed by electrical, compositional and optical measurements before, during and after exposure to these conditions in order to follow the degradation behavior of these layers in time.We have shown that ZnO:Al layers degraded in the presence of a mixture of H2O and CO2. Individually, CO2 does not impact the degradation at all during the tested period, while the individual impact of H2O is small. However, when CO2 is also present, the concentration of OH increases greatly in the bulk and even more at the air/ZnO:Al and in the ZnO:Al/glass interfaces. Carbon based species are then also present, indicating that Zn5(OH)6(CO3)2 is also formed at the grain boundaries. The impact of gaseous O2 as well as water purged with N2 and O2 on ZnO:Al degradation is very small.