How much time is it worth to spend on the various types of cells and their chemical structures and construction methods? Or is it sufficient just to be aware in general of the different cell types (mono, poly, CIGS, CdTe, etc.) and their performance characteristics?
Since you are studying for a Technical Sales Exam, I would recommend not worrying about getting into the different details about the chemistry if you have limited time. It is good to know, however there are many other things that are more likely to be on the exam. Yes it is a good idea to know that Monocrystalline is usually better than Polycrystalline and that CIGS and CdTe are thin film and have a history of being less efficient than crystalline.
That being said, there are interesting developments. It has been in the news recently that the world record efficient CdTe cell has just passes the world record Polycrystalline cell efficiency. The world record efficiencies are interesting, but do not translate to cost effective solutions.
Also, did you know that gallium arsenide is a thin film technology that is more efficient than monocrystalline. Gallium arsenide is also very very expensive and is that they typically use in space. Too expensive for terrestrial PV.
I also like to point out that I would rather have 16 percent efficient tier 1 polycrystalline PV than 15 percent monocrystalline. Mono is usually more efficient, but not always.
Another thing is that polycrystalline silicon often refers to the raw silicon that comes in chunks. Another term used for polycrystalline modules is multicrystalline.