One room is getting too hot in rental house

[Bienes Raices]

The room is a kid's bedroom, and it has a sliding glass door, so the sun comes directly into the room. The last tenants complained about it, so I want to find a solution before the new tenants move in on July 1.

Would putting vertical blinds help at all? Or would it be better to put one of those exterior mats that hangs outside of the house? I have heard that putting tint on the window is a bad idea because it can cause problems with the argon gas that sits between the two panes. Thanks.