Install scrot(sudo apt install scrot),go to your desktop environment's keyboard settings -> application shortcuts. Then create a shortcut that uses that printscreen button and then make it run the scrot command with the desired options which you can find by man scrot. I did a quick peek in the man for you and "scrot -m" should probably do what you are looking for, it captures your screen and saves it to a png image file.
I didn't know if you had a multi-monitor setup, the -m is for multi heads so you can probably just leave out the -m if you only have one screen or only want to capture one screen if you have a multi-monitor setup. You can also give it an option to save all the screenshots into a specific directory and other options, just check the man page if you are looking for something specific.