Although you may not need a one-to-one match for TempDB files and CPU cores, if you do think TempDB is causing a bottleneck, I'd certainly recommend increasing the number of TempDB files from 1. On a number of our servers I've set up 2 files for TempDB (some servers have 2 cores, some have many more) and even just moving to 2 files seems to improve performance.

I also agree with the comment of making the TempDB files as large as possible - the last thing you want is a delay to a transaction because TempDB has to autogrow. But I wouldn't suggest using the whole disk, maybe 80% - that way you've got room to grow in an emergency while you work out what caused all the space to be used up!