My friend is willing to pay rent but I don't want to accept it.
That's strange. Why don't you want to accept his rent?
I want the rent payment to be higher so i want to charge him the higher cost.
I see that you're concerned about your financial state, but if you raise the rent too much, you won't have any tenants because they'll look to rent elsewhere. If you've got a good tenant, you should try to keep him.
I just don't want to struggle with money.
I can understand having money troubles can be stressful, but getting the money by raising rent above the market price is not a good idea. Your friend might move out and then you will have no money at all.