Aluminum doped zinc oxide (ZnO:Al) layers were exposed to the atmospheric gases carbondioxide (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 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 degradation of ZnO:Al was accompanied by the occurrence of holes in the ZnO:Al layer near the ZnO:Al/glass interface. The impact of gaseous O₂ as well as water purged with N₂ and O₂ on ZnO:Al degradation is very small. Complete Cu(In,Ga)Se₂ solar cells were also exposed to unpurged liquid H₂O and H₂O purged with CO₂, O₂, N₂ and air. The samples exposed to H₂O purged with air and CO₂ showed a rapid decrease in efficiency after approximately 180 hours of exposure. This efficiency decrease is mainly driven by a very rapid decrease in current density and an increase in series resistance.

Date Published: 8 October 2014
PDF: 15 pages
Proc. SPIE 9179, Reliability of Photovoltaic Cells, Modules, Components, and Systems VII, 91790K (8 October 2014); doi: 10.1117/12.2061330

Published in SPIE Proceedings Vol. 9179:
Reliability of Photovoltaic Cells, Modules, Components, and Systems VII
Neelkanth G. Dhere, Editor(s)