Why would you want to use backslashes? They’re pretty much only used in file paths on Windows (see this StackExchange answer for a brief history of why), and Windows can also parse forward slashes just fine, so you don’t need to use backslashes on Windows.
Everywhere else (file paths in all other OSes as well as URIs) uses forward slashes, and in many cases will not parse backslashes as directory separators.
If your code is only ever going to be run on a Windows server and nowhere else, and you’re only using the saved paths to generate file paths (not URIs for links, images, etc.), then you should be all right using backslashes – but as soon as you have to either run the code on different architecture or use the path names as part of a URI, then you’ll need to use forward slashes anyway to make it work.
So basically, just always use forward slashes, never backslashes.