Efficient white polymer light-emitting diodes from single polymer exciplex electroluminescence

Efficient white polymer light-emitting diodes were developed based on exciplex electroluminescence from a single polymer PFTS that consists of an electron-donating side chain and an electron-withdrawing backbone. It is noted that the device performances can be dramatically improved by incorporating a certain amount of high triplet energy level poly(9-vinylcarbazole) (PVK) into the emissive layer, which can lead to a more balanced charge carrier and decrease the exciton back transfer from the formed exciplex to the backbone of poly(fluorene-co-dibenzothiophene-5,5-dioxide). The luminous efficiency can be further improved by utilizing PVK as the hole transport layer, which can achieve greenish white emission with a luminous efficiency of 9.12 cd A(-1) and CIE coordinates of (0.25, 0.37). Of particular interest is that the emission of PFTS can be modified by varying the thickness of the emissive layer by virtue of microcavity effects, where the optimized device exhibits a remarkable luminous efficiency of 7.37 cd A(-1) with CIE coordinates of (0.30, 0.43). These observations demonstrated the great promise of utilizing the single polymer with the exciplex emission for the construction of efficient white polymer light-emitting devices.