Is there a reason why you're looking to change the encryption method rather than your approach? It's so pointless to put encryption and charset in the same sentence, think about your reasoning about this request.
Hint: if it's a database insert problem, take a look at PDO.
1.) It's a bad idea to use GET method to propagate (larger set of) data.
2.) GET method has a limit on amount of data you can send, use POST.
3.) Hexing something inflates the data by the factor of 2, you'll hit the limit of the GET method extremely fast and you'll wonder how your thing won't decrypt.
4.) Using hexed data to obfuscate something is generally bad idea because it's extremely easy to notice it.
I'm assuming you're passing some sort of an ID trough the URL and you don't want users to guess numbers by changing the query string.
Well, don't you think that encrypting / decrypting or/and hexing the number is a little too extreme? As I said, change of approach to your problem might be a better solution.