You'll have to clarify a little.
My most simpleminded reading of your request sounds like you want all the contents of all the cells (including some description of the cell formats) all strung together and stored into a single Powershell variable?
Perhaps you mean some sort of array or hashtable?
Or do you mean into a singe Object of some sort that you can later manipulate?
If the last, and your source file is in .xlsx format, and you are comfortable looking at C# examples and translate into powershell, then look at
http://closedxml.codeplex.com/
which I have used to import excel tables.
A simpler one to use is