There is no solution that will give permanent one-way viewing. You can get treatments / films that can be applied to the glass to effectively turn it into a one-way mirror, but the mirror effect is always seen on the side with the brighter ambient light. So during the day, you will see out, people outside will see a mirror. But during the night, if you have a light on in the room, you will see the mirror effect, and those outside will be able to see in.
Obscuring film cal be applied which will let light in, but will mean the view is obscured from both sides.