Bidirectional OLED microdisplay combines a sensor and a display on the same chip by integrating photodiodes between the OLED pixels:
This technology was developed by the the Fraunhofer Institute. For now the demo chip is only monochrome with 320×240 display and 160×120 camera, but there are plans for higher resolution displays (VGA and above). Here is a video (in German) describing this technology:
















