Impact of atmospheric species on copper indium gallium selenide solar cell stability: an overview

An overview of the measurement techniques and results of studies on the stability of copper indium gallium selenide (CIGS) solar cells and their individual layers in the presence of atmospheric species is presented: in these studies, CuðIn; GaÞSe2 solar cells, their molybdenum back contact, and their ZnO:Al front contact were exposed to liquid water purged with gases from the atmosphere, like carbon dioxide (CO2 ), oxygen (O2 ), nitrogen (N2 ), and air. The samples were analyzed before, during, and after exposure in order to define their stability under these conditions. The complete CIGS solar cells as well as the ZnO:Al front contact degraded rapidly when exposed to H2 O combined with CO2 , while they were relatively stable in H2 O purged with O2 or N2. This was caused by either degradation of the grain boundaries in the ZnO:Al film or by the dissolution of part of this film. Uncovered molybdenum films, on the other hand, oxidized rapidly in the presence of H2 O and O2 , while they were more stable in the presence of H2 O with N2 and/or CO2. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.JPE .6.015501] Keywords: copper indium gallium selenide solar cells; CO2, molybdenum; oxygen; water; ZnO:Al. Paper 15060P received Sep. 28, 2015; accepted for publication Jan. 28, 2016; published online Feb. 25, 2016. 1 Introduction Large-scale commercial introduction of copper indium gallium selenide (CIGS) photovoltaics requires modules with high efficiency, low costs, and a long and predictable lifetime. Unfortunately, knowledge about the reliability of CIGS solar cells and modules is still limited, so their lifetime in the field cannot easily be predicted. Since warrantees are given that the modules will still yield 80% of their initial power after 20 years of field exposure,1 more knowledge about the degradation behavior of CIGS solar cells and modules is required. Knowledge about the degradation behavior would also help to...