The main type of transparent TV screen, an OLED screen, has such amazing properties because of the way it's constructed. Basically, OLEDs are composed of a couple of layers of plastic -- the organic, or carbon-based, material in the name -- sandwiched between two layers of glass. That's why you can see right through an OLED screen. The design also includes tiny clear cathodes to inject electrons into the screen, and anodes that enable the electrons to flow out of the device. When you turn on the TV, it sends electricity through the plastic layers, and it reacts with chemicals in the plastic to create the picture on the screen [source: Antonaidis].
One of the advantages an OLED has over a liquid crystal display (LCD), another common type of screen, is that when the electricity goes through the plastic, it actually emits light on its own. An LCD screen, in contrast, only creates the shapes and color. It has to be backlit with another light source. That means that an OLED doesn't require as much electricity as an LCD, and unlike that type of screen, an OLED can produce a true black, by not giving off any light in a certain area. A plasma screen can do some of the same things, but because it has gas inside, it needs to have thicker glass and is bulkier than an OLED, and it isn't as efficient [source: Maxwell].
The OLED has a lot of advantages, but it isn't the only type of transparent TV. Electronics engineers have also come up with ways to make LCD screens transparent as well.