This metal layer is most commonly sputtered Mo which has a target resistivity and allows Na to diffuse from the glass substrate to the upper layers of CdS and CIGS. The thickness and micro-structure of the Mo film is critical to both resistivity and the ability to allow the Na to diffuse. Thickness can be measured by XRR. Microstructure can be characterized by XRD (phase ID), SEM, and AFM. Porosity can be characterized by TEM. Oxygen in the Mo film can affect the properties and this can be determined by XPS and RBS. SIMS can be used to profile the Na through the Mo into the upper layers. If the glass substrate is replaced by a metal foil such as stainless steel, defects in the foil can be characterized by AFM and Auger.
The CIGS layer deposited on the metal contact can be characterized by many techniques. Cross section SEM gives the grain and void morphology. TEM gives information on defects, including nanodomains. STEM/EDS provides information on fluctuations of the ratio of alloy components. SIMS gives the profile of the major constituents (Cu, In, Ga, Se) as well as impurities such as O and C contaminants and the desired Na. Auger can also profile the major constituents. XRD and GIXRD give CIGS phase ID, and XPS provides surface stoichiometry variance before the CdS layer is deposited.
Thickness and composition of the CdS layer can be obtained by XRR and RBS. The TCO layer composition and thickness can be determined by XRR and RBS while XRD can provide phase degradation under accelerated environmental aging tests.
In addition organic contamination that may enter the process at any step, including the module formation, can be determined by FTIR, GCMS, XPS, Raman, or TOF-SIMS.