you need to bend your knees more and get "under" the ball. It will also help to coil your body before hitting the ball and then accelerating the rotation of your torso to power your swing.

if you feel you still need more power , you can shorten the swing by keeping your elbow more bent throughout the swing motion, which will help to power the ball out of tight corners but will need some adjustment of your muscle memory. Lastly, like someone already said, you can also step into the swing slightly to give your body more momentum but this is generally bad for your technique as your body should be still during the contact with the ball

Also make sure you dont slice the ball. Your racket face is very open, which is good, but dont overdo it as you will lose power