\addtocontents is mainly intended to be used to enter formatting information (extra spacing, for example) not directly related to any particular actual line of contents of the ToC; if you want to introduce some text together with some information (such as the page number) and some formatting (such as the one used for a particuar sectional unit), then you might want to use
If used together with the
hyperref package, a
\phantomsection command should also be included to get the proper result for the hyperlinks in the table of contents and for the bookmarks.
EDIT: since you don't want the page number nor any special formatting for the text to be included, then you can use