Efficient polarized light-emitting diodes utilizing ultrathin photoaddressable alignment layers

We demonstrate that an ultrathin photoaddressable polymer (PAP) layer with a thickness as small as 5 nm can be utilized for the monodomain alignment of thermotropic liquid crystalline polyfluorene. The optical anisotropies in absorption and emission are found to be independent of the PAP layer thickness within a range of 5 to 30 nm. On the other hand, decreasing the PAP layer thickness greatly improves the performance of polarized blue light-emitting diodes: With a PAP layer thickness of only 10 nm, the device turns on at 5 V and reaches a brightness of 100 cd/m2 at 8 V with an efficiency of 0.66 cd/A.