This paper (2012) shows that it is possible to create LEDs by printing zinc oxide and a conducting polymer on paper: http://liu.diva-portal.org/smash/get/diva2:

This paper (2012) shows that it is possible to create LEDs by printing zinc oxide and a conducting polymer on paper: http://liu.diva-portal.org/smash/get/diva2:515790/FULLTEXT01 http://liu.diva-portal.org/smash/get/diva2:515790/FULLTEXT01 Maybe it's derived from this technique?